This review explores how water impacts zeolite structure, stability, and catalysis, including acidity modulation via hydrogen bonding and hydronium ion formation. It examines strategies for water removal from zeolites and highlights advanced in-situ techniques, such as Fourier Transform Infrared (FTIR) spectroscopy and solid-state Nuclear Magnetic Resonance (NMR), to achieve precise characterization. Insights into challenges and future advancements are provided.

Phosphorus modification is a widely adopted strategy for modulating the performance of ZSM-5 catalysts in methanol-to-hydrocarbon (MTH) reactions. However, the underlying modification mechanism for the structure–performance relationship is not yet fully understood. In this study, a series of phosphorus-modified ZSM-5 (P-ZSM-5) catalysts were synthesized via direct impregnation using ammonium phosphate dibasic as the phosphorus source. With this synthetic method, the aluminum content and structural properties of zeolite are preserved. Our findings showed that phosphorus loading significantly alters the acidity and microporous properties of ZSM-5. To explore the underlying reasons for these changes, we employed ³¹P and ²⁷Al solid-state magic angle spining (MAS) nuclear magnetic resonance (NMR), which provided chemical and structural insights. The lower amount of strong acid sites resulted in a prolonged lifetime in the MTH reaction and enhanced selectivity toward alkenes for P-ZSM-5. Additionally, the pore narrowing created by adding phosphorus had an additional effect on product selectivity by suppressing o-xylene yields. By using the ¹³C, ¹³C–¹³C, and ¹H–¹³C MAS NMR analysis conducted on the ¹³C-methanol-reacted catalysts, we demonstrated direct evidence that P-ZSM-5 preserved the same MTH pathways but suppressed the formation of one of the key coke precursors, the 1,2,3-trimethylcyclopentenyl cation. This was further confirmed by the operando UV–vis results, along with the reduced accumulation rate of other coke precursors such as naphthalene and polyaromatics.

Given that ethanol can be obtained from abundant biomass resources (e.g., crops, sugarcane, cellulose, and algae), waste, and CO₂, its conversion into value-added chemicals holds promise for the sustainable production of high-demand chemical commodities. Nonoxygenated chemicals, including light olefins, 1,3-butadiene, aromatics, and gasoline, are some of the most important of these commodities, substantially contributing to modern lifestyles. Despite the industrial implementation of some ethanol-to-hydrocarbons processes, several fundamental questions and technological challenges remain unaddressed. In addition, the utilization of ethanol as an intermediate provides new opportunities for the direct valorization of CO and CO₂. Herein, the recent advances in the design of ethanol conversion catalysts are summarized, providing mechanistic insights into the corresponding reactions and catalyst deactivation, and discussing the related future research directions, including the exploitation of active site proximity to achieve better synergistic effects for reactions involving ethanol.

Extra-framework aluminum (EFAl) species are known to alter the acidic nature of zeolites and therefore their catalytic properties. Although it has been reported that the formation of such species leads to a change in the concentration and strength of acidity, the influence of those on hydrocracking warrants further exploration. To investigate these concepts, faujasite zeolite (ultrastable Y, USY) samples with various SiO₂/Al₂O₃ ratios were steamed at different conditions until they showed similar hydrocracking activity to the reference USY sample. The steaming process results in zeolite samples with similar catalytic activity and selectivity but different levels of EFAl. Hexane cracking tests and pentylamine adsorption followed by two-dimensional ¹H–²⁷Al heteronuclear nuclear magnetic resonance spectroscopy show that samples with a high number of EFAl sites have a larger number of those species in close proximity to the Brønsted acid site (BAS). After the extensive characterization, we concluded that the catalytic activity and product selectivity in hydrocracking is unrelated to both Brønsted acid strength and EFAl species near BAS, leaving the number of BAS as the main activity descriptor.

In the context of advancing social modernization, the projected shortfall in the demand for renewable aromatic hydrocarbons is expected to widen, influenced by industries like high-end materials, pharmaceuticals, and consumer goods. Sustainable methods for aromatic production from alternative sources, particularly the methanol-to-aromatics (MTA) process using zeolite ZSM-5 and associated with the “methanol economy”, have garnered widespread attention. To facilitate this transition, our project consolidates conventional strategies that impact aromatics selectivity—such as using hierarchical zeolites, metallic promoters, or altering zeolite physicochemical properties—into a unified study. Our findings demonstrate the beneficial impact of elongated crystal size and heightened zeolite hierarchy on preferential aromatics selectivity, albeit through distinct mechanisms involving the consumption of shorter olefins. While metallic promoters enhance MTA performance, crystal size, and hierarchy remain pivotal in achieving the maximized aromatics selectivity. This study contributes to a deeper understanding of achieving superior aromatics selectivity through physicochemical modifications in zeolite ZSM-5 during MTA catalysis, thereby advancing the field’s comprehension of structure–reactivity relationships.

Over 70 years, silica–magnesia catalyst prepared by wet-kneading method has been a benchmark for one-step ethanol-to-butadiene Lebedev process. Recent studies showed that wet-kneading provides an environment for the concomitant dissolution and cross-deposition of silicon and magnesium subunits, which can lead to the formation of not only the beneficial sites (Si on MgO), but also the detrimental ones (Mg on SiO2) for the Lebedev process. The use of conventional silica sources to formulate the silica–magnesia catalysts should be revisited, as they will be eventually dissolved and redispersed on MgO and the remaining SiO2 particles would be used for the formation of detrimental sites. In this regard, we demonstrated core–shell structured MgO–SiO2 catalysts as a second generation of Lebedev catalyst, where the Si subunits were selectively deposited on the MgO nanoparticles as surface magnesium silicates. Compared to the conventional wet-kneaded silica–magnesia catalyst system, we could reduce the amount of Si source by ∼40 times with the enhanced catalytic performance towards butadiene.

In this work, we show that the acid-site density controls the dominant cycle during the methanol-to-hydrocarbons reaction on beta zeolite. Our experimental evidence is based on the study of beta zeolites with very similar diffusional pathways and different aluminum content. High selectivity to propylene was observed for samples with low Brønsted acid-site density, which is a consequence of the promotion of the olefinic cycle. Our results also confirm that the production of ethylene via the olefinic cycle is negligible. In contrast, high ethylene and aromatics are found at a high Brønsted acid-site density, highlighting the predominancy of the aromatic cycle. Operando UV–vis data show that monoenylic carbocationic species predominate on the olefinic cycle, whereas the aromatic cycle is dominated by polyalkylated monoaromatics. Analysis of the spectroscopy data also shows a linear correlation of the formation of polyaromatic species with the Brønsted acid-site density.

Defect engineering has emerged as a promising strategy to enhance the photocatalytic properties of metal–organic frameworks (MOFs). In this study, we investigate the influence of the introduction of defects into a Ti-based MOF, ACM-1, on its photocatalytic activity for hydrogen evolution reaction. Through solid-state NMR and XPS analysis, we define the structural defects as a fluoride inclusion. Our results demonstrate a remarkable 5-fold increase in photocatalytic activity compared to pristine ACM-1. Density functional theory (DFT) calculations reveal that the presence of fluorine atoms stabilizes titanium orbitals, leading to a reduced band gap. This reduction in the band gap is identified as the key mechanism underlying the enhanced photocatalytic activity. Our findings highlight the efficacy of defect engineering through TFA-mediated fluoride inclusion in improving the photocatalytic performance of Ti-based MOF ACM-1.

Here, we report the synthesis of new functional monomers of dicyclopentadiene (DCPD) by esterification with carboxylic acids that can be derived from biomass. We demonstrate that the esterification of DCPD proceeds via a reaction intermediate, that is, cydecanol (DCPD-OH), and propose an esterification mechanism over solid acid catalysts.

The tandem CO2 hydrogenation to hydrocarbons over mixed metal oxide/zeolite catalysts (OXZEO) is an efficient way of producing value-added hydrocarbons (platform chemicals and fuels) directly from CO2 via methanol intermediate in a single reactor. In this contribution, two MAPO-18 zeotypes (M = Mg, Si) were tested and their performance was compared under methanol-to-olefins (MTO) conditions (350 °C, PCH3OH = 0.04 bar, 6.5 gCH3OH h–1 g–1), methanol/CO/H2 cofeed conditions (350 °C, PCH3OH/PCO/PH2 = 1:7.3:21.7 bar, 2.5 gCH3OH h–1 g–1), and tandem CO2 hydrogenation-to-olefin conditions (350 °C, PCO2/PH2 = 7.5:22.5 bar, 1.4–12.0 gMAPO-18 h molCO2–1). In the latter case, the zeotypes were mixed with a fixed amount of ZnO:ZrO2 catalyst, well-known for the conversion of CO2/H2 to methanol. Focus was set on the methanol conversion activity, product selectivity, and performance stability with time-on-stream. In situ and ex situ Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), sorption experiments, and ab initio molecular dynamics (AIMD) calculations were performed to correlate material performance with material characteristics. The catalytic tests demonstrated the better performance of MgAPO-18 versus SAPO-18 at MTO conditions, the much superior performance of MgAPO-18 under methanol/CO/H2 cofeeds, and yet the increasingly similar performance of the two materials under tandem conditions upon increasing the zeotype-to-oxide ratio in the tandem catalyst bed. In situ FT-IR measurements coupled with AIMD calculations revealed differences in the MTO initiation mechanism between the two materials. SAPO-18 promoted initial CO2 formation, indicative of a formaldehyde-based decarboxylation mechanism, while CO and ketene were the main constituents of the initiation pool in MgAPO-18, suggesting a decarbonylation mechanism. Under tandem CO2 hydrogenation conditions, the presence of high water concentrations and low methanol partial pressure in the reaction medium led to lower, and increasingly similar, methanol turnover frequencies for the zeotypes. Despite both MAPO-18 zeotypes showing signs of activity loss upon storage due to the interaction of the sites with ambient humidity, they presented a remarkable stability after reaching steady state under tandem reaction conditions and after steaming and regeneration cycles at high temperatures. Water adsorption experiments at room temperature confirmed this observation. The faster activity loss observed in the Mg version is assigned to its harder Mg2+-ion character and the higher concentration of CHA defects in the AEI structure, identified by solid-state NMR and XRD. The low stability of a MgAPO-34 zeotype (CHA structure) upon storage corroborated the relationship between CHA defects and instability.

Zeolites have been successfully applied on a wide range of reaction processes (Methanol to Hydrocarbons, Fluid Catalytic Cracking, etc) and continue to attract academic and industrial investigations. Understanding of the reaction mechanisms involved in zeolite catalysis has been a long standing issue due to the wide range of intermediates and products involved, which has hindered the industrial implementation of these materials. Thus, in order to determine and discriminate between each type of compound involved in the complex reaction mixture, computational simulations have been applied to analyse the 13C chemical shifts of a wide range of known or proposed intermediates and products. The first part of this study focuses on calculating the 13C chemical shifts of C1-C3 compounds commonly part of the reactant feed, comparing the results of mobile versus immobile states and determining which compounds could have their 13C chemical shifts superimposed over others. The second part focuses on C4-C6 olefins, analysing the differences stemming from: position of double bond, ramified structure, mobile and chemical state. Finally, the third part translates the same approach from the olefins study on aromatic derivatives.

We studied the epoxidation of dicyclopentadiene (DCPD) with hydrogen peroxide over different heterogeneous catalysts. Among them, niobium pentoxide (Nb2O5) catalysts showed promising catalytic activity, giving mono- and di-epoxy DCPD with low amounts of epoxidation byproducts. The epoxidation activity of Nb2O5 largely depends on the reaction solvents. Higher epoxidation performance was observed in the solvents with a certain range of dielectric constants (30 < εr < 40), such as methanol and acetonitrile. The crystallinity of the Nb2O5 catalysts was modified by calcination temperature, which influences the formation of surface peroxo species, and consequently, the extent of the DCPD epoxidation.

Zeolites stand as a pillar for industrial catalysis, whose Brønsted acidity is intimately correlated with tetrahedral aluminum species. To better understand the influence of aluminum distribution on Brønsted acid-catalyzed reactions, major advances in this field require a delicate design of zeolite catalysts together with an advanced characterization of such materials. We demonstrate that at the microscopic level, two framework aluminum atoms in proximity lead to the formation of paired acid sites possessing higher activities for various Brønsted acid-catalyzed reactions, such as methanol to aromatics. At the mesoscopic level, locating aluminum atoms at crystal edges not only accelerates progression of reactions in series but also facilitates the engineering of crystals to synthesize hollow structures showing a significant improvement on aromatic yield. Our work improves the understanding of complex reaction networks and illustrates how to develop high-performing zeolite catalysts by controlling acid sites distribution at the nanoscale and the microscale.

Wet-kneaded silica–magnesia is a benchmark catalyst for the one-step ethanol-to-butadiene Lebedev process. Magnesium silicates, formed during wet kneading, have been proposed as the active sites for butadiene formation, and their properties are mainly explained in terms of the ratio of acid and base sites. However, their mechanism of formation and reactivity have not yet been fully established. Here we show that magnesium silicates are formed by the dissolution of Si and Mg subunits from their precursors, initiated by the alkaline pH of the wet-kneading medium, followed by cross-deposition on the precursor surfaces. Using two individual model systems (Mg/SiO₂ and Si/MgO), we demonstrate that the location of the magnesium silicates (that is, Mg on SiO₂ or Si on MgO) governs not only their chemical nature, but also the configuration of adsorbed ethanol and resulting selectivity. By using an NMR approach together with probe molecules, we demonstrate that acid and basic sites in close atomic proximity (~5 Å) promote butadiene formation.

Tungsten is the most interesting and promising metal to replace molybdenum in methane dehydroaromatization (MDA) catalysis. Located in the same column of the periodic table, tungsten displays similar chemical features to molybdenum (i.e., formation and stability of oxidation states, acidity of trioxides, tendency toward formation of polynuclear species, atomic radii, ionic radii, etc.) but shows higher thermal stability. The latter could be an advantage during high-temperature reaction–regeneration cycles. However, the MDA activity of W–ZSM-5 catalysts is much lower than the activity obtained with their Mo counterpart. In order to gain a further understanding of such differences in catalytic activity, we present a thorough investigation of the effect of dispersion and distribution of W sites on the zeolite, their relation with catalytic activity, and the temporal evolution of dispersion with reaction–regeneration cycles. The structure of W sites is elucidated with advanced and detailed characterization techniques, including operando X-ray absorption spectroscopy (XAS). The information obtained can help the catalysis community to design better W catalysts for MDA and other reactions (i.e., metathesis, hydrocarbon cracking, hydrodesulfurization, isomerization, etc.) where this is the metal of choice.

The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT, Pd carbonyl IR band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2. The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd2+/Zn2+ carbonyls appear due to ion exchange into SAPO-34 framework.

Epoxidation of dicyclopentadiene (DCPD) is studied on a series of TiO₂ catalysts using hydrogen peroxide as an oxidant. DCPD derivatives have applications in several areas including polymer, pharmaceutical and pesticide products. The control of selectivity leading to the desired product is important for many of these applications. Using experimental and computational studies, we show that the surface crystalline phases of TiO₂ play crucial roles not only in the formation of peroxo species but also in the selective epoxidation of two different CC double bonds in DCPD.

Alkyl levulinates (alkyl‒LA) are biomass derived, versatile chemicals for flavours, chemical solvents and fuel additives. In this work, we used furfuryl alcohol (FFA) to synthesise alkyl‒LA and systematically investigated the FFA alcoholysis using batch and continuous reactors . We screened various solid acid catalysts in the batch reactor system and found that Amberlyst‒15 resin performed best, not only showing high levels of alkyl‒LA yields, but also suppressing the amount of undesired dialkyl ether. We observed two plausible intermediates (alkoxy‒methylfuran and tri-alkoxy-pentanone) during the FFA alcoholysis. In the continuous reactor system, the water content in the reaction mixture influenced the conversion of FFA as well as the yield of alkyl‒LA, providing additional reaction pathways (e.g., ring opening of FFA). For the first time, we demonstrated a branched C8 alcohol (2‒ethyl‒1‒hexanol, ethylhexanol) can be used to obtain the corresponding levulinate (2‒ethyl‒1‒hexyl‒LA, ethylhexyl‒LA). With the optimised reaction conditions, we could obtain ethylhexyl‒LA with the yield of 83% and 98% in the batch and continuous reactor system, respectively.

The increasing demand for base chemicals i.e., ethylene and propylene, along with the expected peak in gasoline and fuels demand, are stirring intense research into refineries to be built around processes that maximize the production of chemicals (oil to chemicals, OTC, processes). One of the main challenges at hand for OTC technologies is the formulation of appropriate catalysts able to handle the wide boiling point of the feed and to withstand continuous operation at industrial scale. Hydrothermal degradation, coke deposition and the presence of impurities, such as metals, sulfur and nitrogen containing species, in the feedstock affect catalyst lifetime, activity and selectivity. In this work, we evaluate long term catalyst stability along with the main causes of reversible and irreversible catalyst deactivation. Our results demonstrate that formulation prevents, to a large extent, the degradation of the zeolitic components of the catalyst. Metal deposition, on the other hand, results in a slight decrease in activity along with partial changes in selectivity patterns. The main reasons behind these changes are discussed in detail with the help of extensive characterization.

In the current petrochemical market, the global demand for aromatics, especially benzene, toluene, and xylenes (BTXs), has increased sharply. The methanol-to-aromatic conversion (MTA) over ZSM-5 is among the most promising routes to satisfy this ever-growing demand. In this work, we show that high-pressure operation during MTA leads to a large increase in aromatic selectivity while enhancing stability on-stream. Stable operation along with a very high selectivity to aromatics (up to 50%, with 20% BTXs) can be achieved on a commercial high-silica ZSM-5 (SiO₂/Al₂O₃ = 280) at 400 °C, 30 bar total pressure, and WHSV = 8 h^–1. The high partial pressure of primary olefins and the promoted methanol-induced hydrogen-transfer pathway result in an exponential increase in aromatization, while the high partial pressure of steam generated via dehydration of methanol leads to in situ coke removal and, therefore, to a much slower deactivation of the zeolite.

The Lebedev process, in which ethanol is catalytically converted into 1,3-butadiene, is an alternative process for the production of this commodity chemical. Silica–magnesia (SiO₂–MgO) is a benchmark catalyst for the Lebedev process. Among the different preparation methods, the SiO₂–MgO catalysts prepared by wet-kneading typically perform best owing to the surface magnesium silicates formed during wet-kneading. Although the thermal treatment is of pivotal importance as a last step in the catalyst preparation, the effect of the calcination temperature of the wet-kneaded SiO₂–MgO on the Lebedev process has not been clarified yet. Here, we prepared and characterized in detail a series of wet-kneaded SiO₂–MgO catalysts using varying calcination temperatures. We find that the thermal treatment largely influences the type of magnesium silicates, which have different catalytic properties. Our results suggest that the structurally ill-defined amorphous magnesium silicates and lizardite are responsible for the production of ethylene. Further, we argue that forsterite, which has been conventionally considered detrimental for the formation of ethylene, favors the formation of butadiene, especially when combined with stevensite.

Zeolite-based catalysts are globally employed in many industrial processes, such as in crude-oil refining and in the production of bulk chemicals. However, to be implemented in industrial reactors efficiently, zeolite powders are required to be shaped in catalyst bodies. Scale-up of zeolite catalysts into such forms comes with side effects to its overall physicochemical properties and to those of its constituting components. Although fundamental research into “technical” solid catalysts is scarce, binder effects have been reported to significantly impact their catalytic properties and lifetime. Given the large number of additional (in)organic components added in the formulation, it is somehow surprising to see that there is a distinct lack of research into the unintentional impact organic additives can have on the properties of the zeolite and the catalyst bodies in general. Here, we systematically prepared a series of alumina-bound zeolite ZSM-5-based catalyst bodies, with organic additives such as peptizing, plasticizing, and lubricating agents, to rationalize their impacts on the physicochemical properties of the shaped catalyst bodies. By utilizing a carefully selected arsenal of bulk and high-spatial resolution multiscale characterization techniques, as well as specifically sized bioinspired fluorescent nanoprobes to study pore accessibility, we clearly show that, although the organic additives achieve their primary function of a mechanically robust material, uncontrolled processes are taking place in parallel. We reveal that the extrusion process can lead to zeolite dealumination (from acid peptizing treatment, and localized steaming upon calcination); meso- and macropore structural rearrangement (via burning-out of organic plasticizing and lubricating agents upon calcination); and abating of known alumina binder effects (via scavenging of Al species via chelating lubricating agents), which significantly impact catalytic performance. Understanding the mechanisms behind such effects in industrial-grade catalyst formulations can lead to enhanced design of these important materials, which can improve process efficiency in a vast range of industrial catalytic reactions.

Ziegler-Natta catalysts for olefin polymerization are intrinsically complex multi-component systems. The genesis of the active sites involves several simultaneous and sequential steps, making the individual steps and interconnections difficult to be unraveled in an unambiguous manner. In this work, we combine X-ray diffraction and spectroscopy to probe each step of the birth and life of a MgCl₂-based Ziegler-Natta catalyst, namely the formation of high surface area MgCl₂ by dealcoholation of an alcoholate precursor, the TiCl₄ grafting, and the subsequent activation by triethylaluminum as co-catalyst. The so-prepared catalyst was tested towards ethylene polymerization, leading to the production of mainly crystalline high-density polyethylene. The use of operando characterization techniques allowed probing the transient details that are difficult to be dissected in the aftermath, but can radically affect the overall catalytic process.

Levulinate esters are important chemical compounds usually obtained by esterification of levulinic acid derived from cellulose. We studied the synthesis of levulinate esters from furfuryl alcohol using graphite oxide (GO) and reduced graphite oxide (rGO) catalysts. The GO and rGO provided close to 100% selectivity to levulinate at a reaction temperature of 110 °C. The reaction rate and selectivity were largely influenced by changing the number of oxygen-containing groups on the catalyst surface. With an increased supply of biomass-derived chemicals, the demonstrated catalytic features of the family of graphite make them good candidates for application in biorefineries.

The synthesis of many industrial bulk and fine chemicals frequently involves electrophilic aromatic substitution (S_EAr) reactions. The most widely practiced example of the S_EAr mechanism is the zeolite-catalysed ethylation of benzene, using ethylene as an alkylating agent. However, the current production route towards ethylbenzene is completely dependent on fossil resources, making the recent commercial successes in the zeolite-catalysed benzene ethylation process using bioethanol (instead of ethylene) very encouraging and noteworthy. Unfortunately, there is no information available on the reaction mechanism of this alternative synthesis route. Here, by employing a combination of advanced solid-state NMR spectroscopy and operando UV-Vis diffuse reflectance spectroscopy with on-line mass spectrometry, we have obtained detailed mechanistic insights into the bioethanol-mediated benzene ethylation process through the identification of active surface ethoxy species, surface-adsorbed zeolite–aromatic π-complexes, as well as the more controversial Wheland-type σ-complex. Moreover, we distinguish between rigid and mobile zeolite-trapped organic species, providing further evidence for distinctive host–guest chemistry during catalysis.

Wet-kneading is a technique commonly used for the synthesis of SiO₂–MgO catalysts for the Lebedev ethanol-to-butadiene process, with catalyst performance known to depend heavily on the preparation parameters used in this method. Here, the large influence of Mg precursor and MgO content on morphology, chemical structure (as determined by TEM(-EDX), FT-IR, XRD and solid-state ¹H–²⁹Si cross-polarized MAS NMR), and on catalyst performance is demonstrated. The Mg precursor used is found to influence the extent of magnesium silicate formation during wet-kneading, as estimated from TEM and FT-IR, which, in turn, was found to correlate with catalyst performance. Accordingly, the catalyst synthesized from a nanosized Mg(OH)₂ precursor (SiO₂–MgO (III)_nano), showing the highest degree of chemical contact between the SiO₂ and MgO components, gave the highest butadiene yield. Variation of the Mg/Si ratio in a series of SiO₂–MgO (III)_nano materials showed a volcano-type dependence of the butadiene yield on MgO content. ¹H–²⁹Si CP-MAS NMR studies allowed for the identification of the type and an estimation of the amount of magnesium silicates formed during wet-kneading. Here, we argue that the structural characteristics of the hydrous magnesium silicates, lizardite and talc, formed during catalyst preparation, together with the ratio of the magnesium silicates to MgO, determine the overall acid/base properties of the SiO₂–MgO (III)_nano catalyst materials and as a result, catalyst performance.

Pd–Cu supported on TiO₂–CeO₂ mixed oxides (Pd–Cu/TiO₂–CeO₂) were tested for the reduction of nitrate ions in water. Compared with a Pd–Cu catalyst with TiO₂ only as support (Pd–Cu/TiO₂), which was proved to be active for this reaction in our previous study, Pd–Cu/TiO₂–CeO₂ showed improved activity if TiO₂–CeO₂ contained an appropriate amount of ceria (Ti:Ce = 18:1). Especially, the Pd–Cu/TiO₂–CeO₂ (Ti:Ce = 18:1) showed the initial nitrate reduction rate of 3.20 mmol/min/g_cat, eight times higher than that of Pd–Cu/TiO₂(0.41 mmol/min/g_cat). It was supposed that the improved activity of the catalyst was attributable to the reduced surface (oxygen vacancies) of the support and zero-valence states of the active metals (including the Pd–Cu alloy) in the catalyst.

In this study, Cs-exchanged phosphotungstic acids (Cs_xH_3−xPW₁₂O₄₀, x = 1–3) were examined as a catalyst for the hydrocracking of extra-heavy oil (vacuum residue, API gravity = 2.3°). Cs_xH_3−xPW₁₂O₄₀ showed a higher activity than the commercially available, NiMo/Al₂O₃-based catalyst in the hydrocracking of extra-heavy oil; the former catalyst produced a larger quantity of liquid oils than the commercial catalyst. The liquid oils produced by the phosphotungstic acids were slightly heavier than those produced by the commercial catalyst. They also showed comparable activities to the commercial catalyst in terms of the hydrogenative removal of metals (nickel, vanadium) and sulfur from the extra-heavy oil. It was found that the hydrocracking performance was primarily dependent on the surface acid density of heteropolyacids. The best performance of the Cs_xH_3−xPW₁₂O₄₀ catalysts was obtained at a Cs loading of x = 2.2, where the surface acid density was highest. To assess the physical and chemical properties of the catalysts, various characterization techniques were used, including inductively coupled plasma-mass spectrometry, X-ray diffraction, thermogravimetric analysis, Fourier transform-infrared spectroscopy, Brunauer–Emmett–Teller analysis, and ammonia-temperature programmed desorption analysis.

The use of high-temperature water (including near/super-critical water) has been studied as a promising reaction method for the valorization of lignocellulose biomass (lignin). The dissociation of lignin usually begins with the cleavage of ether bonds which are the weakest chemical linkages in a lignin structure. Of the ether bonds, the most prevalent type is a β-ether bond; phenethyl phenyl ether (PPE) is regarded as a suitable model compound for studying the cleavage of this bond. This study investigates the conversion of PPE in high-temperature water, with sodium carbonate (Na₂CO₃) serving as an additive to promote ionic pathways. The addition of sodium carbonate greatly enhanced the conversion of PPE and produced phenol as the primary product. It was proposed that phenol was obtained through the dissociation of a Na⁺–PPE adduct, which progressed via heterolytic ether cleavage and α-hydrogen abstraction.

In this study, a novel, strategic method was developed for the synthesis of a mesoporous silica catalyst embedded with ruthenium nanoparticles (RuNPs/SiO₂) by combining the polyol and modified sol–gel methods. By applying this new procedure, uniformly synthesized ruthenium nanoparticles with an average size of 3.8 nm and 95% spherical shape were highly dispersed in the mesoporous silica support material. Coordinated carbonyl groups of PVP remaining from the synthesis of the RuNPs were effectively removed by the thermal treatment (calcined at 573 K for 4 h) and the sythesized RuNPs/SiO₂ catalysts were reduced under hydrogen at 20 bar for 2 h. These catalysts were analyzed using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N₂adsorption–desorption, and X-ray diffraction (XRD). After the thermal treatment and the reduction procedure, the size and shape of the embedded RuNPs were nearly unchanged, and the catalyst was active in the liquid-phase hydrogenation of succinic anhydride (SAN) to selectively form γ-butyrolactone (GBL) with a maximum yield of 90.1%. This novel catalyst preparation is a potentially useful method for the synthesis of metal nanoparticles as heterogeneous catalysts.

In this study, we prepared TiO₂-supported Pd–Cu catalysts of different anatase/rutile phase compositions, which were used in a nitrate reduction in water. It was shown that the catalysts containing a greater anatase phase composition had higher catalytic performance. Through characterization studies using H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), the observed trend of the catalytic activity was correlated to the degree of the strong metal-support interaction (SMSI) over the catalysts. The SMSI occurred through pre-treatment of the catalysts by H₂ reduction (at 200 °C), which resulted in increased partially reduced TiO_2−x and electron-rich active metal (Pd and Cu) states at the catalyst of higher composition of anatase phase. The relationships between the changes in the properties and activities of the catalysts as a result of the anatase phase composition are discussed.

The effect of alumina-based catalysts modified by cerium sulfate on the decomposition CF₄ at reaction temperatures below 700 °C was studied. The catalyst characteristics were determined using various techniques, including X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, ammonia temperature-programmed desorption (NH₃-TPD), elemental analysis (EA) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) to relate the catalytic reactivity with the catalyst properties. The existence of sulfate in alumina-based catalysts provided good catalytic performance due to the increased number of total acidic sites, especially strongly acidic sites, relative to the non-sulfated catalysts. When the catalysts were modified by cerium that could be higher stability in alumina-based catalysts, AlF₃ phase that alumina catalyst can be transformed to in CF₄ hydrolytic decomposition was not observed on the catalysts. We concluded that the existence of sulfate and cerium in alumina-based catalysts influenced the acid properties, phase composition and specific surface area of the catalysts, which in turn affected the catalyst performance.

In this study, we investigated the activity of Pd and Cu co-incorporated on mesoporous silica support such as MCM-41 and SBA-15 for catalytic nitrate reduction in water. In pure hydrogen flow, nitrate concentration was gradually decreased with the reaction time, but nitrogen selectivity was too low due to very high pH of reaction medium after the reaction. In order to acquire high nitrogen selectivity, we utilized carbon dioxide as a pH buffer, which resulted in higher nitrogen selectivity (about 40%). For the above reaction conditions, Pd-Cu/MCM-41 showed better performance than Pd-Cu/SBA-15. The physicochemical properties of both catalysts were investigated to figure out the relationship between the characteristics of the catalysts and the catalytic activity on the catalytic nitrate reduction by N₂ adsoprtion-desorption, X-ray diffraction (XRD), H₂-temperature programmed reduction, X-ray photoelectron spectroscopy (XPS) techniques.

In this study, Pt/Fe/ZSM5 catalysts were applied to oxidation of ammonia, where the catalysts showed good low-temperature activity (≤200 °C) for converting ammonia into nitrogen. With 1.5% Pt/0.5% Fe/ZSM5 catalyst, we could obtain 81% NH₃ conversion and 93% N₂ selectivity at 175 °C at the short contact-time of w/f = 0.00012 g min/mL. Through the characterization studies using high-resolution transmission electron microscopy (HRTEM) and X-ray spectroscopies (XRD, XPS), we could find that the active species was collaborating Pt/Fe species, which structure and activity were largely influenced by support material – in a positive way by ZSM5, rather than by Al₂O₃ and SiO₂. When using ZSM5 as the support material, Pt was highly dispersed exclusively on the Fe oxide, and the valence state and dispersion of Pt changed according to Fe loading amount.

In this study, a strategy was developed for the synthesis of nano-sized, silica–ceria, core–shell composites in a water–oil (W/O) microemulsion consisting of water, heptane and the binary surfactants AOT (sulfosuccinic acid bis (2-ethylhexyl) ester sodium salt) and NP-5 (polyoxyethylene (5) nonylphenyl ether). The core–shell, silica–ceria particles were prepared in a stepwise procedure: (1) the precipitation of the core-silica particles in a W/O microemulsion and (2) the surface precipitation of ceria on the core silica dispersed over the microemulsion. The composition of the binary surfactant greatly influenced the growth rate of the core-silica particles. The virial coefficient of diffusion was utilized to estimate the effect of the surfactant composition on the degree of intermicellar interaction that is important for the growth rate of the silica along with the flexibility of the micellar interface and the structure of the water domain. The deposition of the ceria on the core silica was not straightforward because the bulk and surface precipitation competed with each other. The promotion of surface precipitation was attempted by: (1) chemically modifying the silica surface with an organoamine group and (2) slowing down the precipitation rate of the ceria in a semi-batch operation. These attempts successfully produced the nano-sized silica–ceria, core–shell particles, which were evidenced through the TEM, XPS and zeta potential analysis.

Plant biomass has been proposed as an alternative source of petroleum-based chemical compounds. Especially, aromatic chemical compounds can be obtained from lignin by depolymerization processes because the lignin consist of complex aromatic materials. In this study, kraft lignin, the largest emitted substance among several kinds of lignin in Korea, was used as a starting material and was characterized by solid-state $^{13}C$-Muclear Magnetic Resonance($^{13}C$-NMR), Fourier Transform Infrared Spectroscopy(FT-IR), Elemental Analysis(EA). The depolymerization of kraft lignin was studied at water-phenol mixture solvent in near critical region and the experiments were conducted using a batch type reactor. The effects of water-to-phenol ratio and reaction temperature($300-400^{\circ}C$) were investigated to determine the optimum operating conditions. Additionally, the effects of formic acid as a hydrogen-donor solvent instead of $H_2$ gas were examined. The chemical species and quantities in the liquid products were analyzed using gas chromatography-mass spectroscopy(GC-MS), and solid residues(char) were analyzed using FT-IR. GC-MS analysis confirmed that the aromatic chemicals such as anisole, o-cresol(2-methylphenol), p-cresol(4-methylphenol), 2-ethylphenol, 4-ethylphenol, dibenzofuran, 3-methyl cabazole and xanthene were produced when phenol was added in the water as a co-solvent.

Biodiesel is a renewable fuel which can be produced through an esterification reaction. The cost of feedstock which resulted in that of biodiesel is a large problem to be resolved. Dark oil from industrial process can be a better alternative for biodiesel production because of its low price. In spite of this, the study of biodiesel production using the dark oil has not been reported. This study provides technical information and catalytic properties on this system. Among the several catalysts, WO₃/ZrO₂ catalyst was the most effective catalyst in the esterification of the dark oil to fatty acid methyl esters (FAMEs). The catalytic reaction parameters were optimized that 20 wt.% WO₃/ZrO₂ has a high FFA conversion of 96% at 150 °C, 0.4 g/ml (oil), 1:9 (oil to alcohol, molar ratio) and 2 h reaction time. The physical and chemical properties of the catalyst were characterized by XRD, Raman spectrometer, BET and NH₃-TPD.

Tungsten oxide zirconia, sulfated zirconia and Amberlyst-15 were examined as a catalyst for a conversion of used vegetable oils (VOs) to fatty acid methyl esters (FAMEs). Among them, tungsten oxide zirconia was a promising heterogeneous catalyst for the production of biodiesel fuels from used VOs because of high activity in the conversion over 93% and no leaching WO₃ in the esterification reaction. The reaction conditions were optimized. A study for optimizing the reaction parameters such as the reaction temperature, stirring speed, WO₃ loading over ZrO₂ and reaction time, was carried out. The catalyst was characterized by BET, XRD, FT-IR, and NH₃-TPD. With increasing WO₃ loading over ZrO₂, the triclinic phase of WO₃ increased and the tetragonal phase of zirconia was clearly generated. The highest acid strength of 20 wt% tungsten oxide zirconia catalyst was confirmed by NH₃-TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction.