Search

Multifunctional catalysts have received considerable attention in the cascade reactions of biomass processing. A cascade (or tandem) reaction is realized when multiple reaction steps that require different catalysts are performed in a one-step process. These reactions require bi- or multifunctional catalysts or catalyst mixtures to serve successfully at each reaction step. In this review article, we discuss the major factors of the catalyst design influencing the structure–property relationships, which could differ depending on the catalyst type. The major factors include the amounts and strengths of acidic and basic sites, interactions between those and metal sites, synergetic effects, nanoparticle sizes and morphology, nanostructures, porosity, etc. The catalysts described in this review are based on zeolites, mesoporous solids, MOFs, and enzymes. The importance of continuous cascade processes is also examined. [ABSTRACT FROM AUTHOR]

The alkylation reaction of aromatic compounds gains considerable attention because of its wide application in bulk and fine chemical production. Aromatics alkylated with olefins is a well-known process, particularly for linear alkylbenzene, phenyloctanes, and heptyltoluene production. As octane boosters and precursors for various petrochemical and bulk chemical products, a wide range of alkylated compounds are in high demand. Numerous unique structures have been proposed in addition to the usual zeolites (Y and beta) utilized in alkylation procedures. The inevitable deactivation of industrial catalysts over time on stream, which is followed by a decrease in catalytic activity and product selectivity, is one of their disadvantages. Therefore, careful consideration of catalyst deactivation regarding the setup and functioning of the process of catalysis is necessary. Although a lot of work has been carried out to date to prevent coke and increase catalyst lifespan, deactivation of the catalyst is still unavoidable. Coke deposition can lead to catalyst deactivation in industrial catalytic processes by obstructing pores and/or covering acid sites. It is very desirable to regenerate inactive catalysts in order to remove the coke and restore catalytic activity at the same time. Depending on the kind of catalyst, the deactivation processes, and the regeneration settings, each regeneration approach has pros and cons. In this comprehensive study, the focus was on discussing the reaction mechanism of 1-octene isomerization and toluene alkylation as an example of isomerization and alkylation reactions that occur simultaneously, shedding light in detail on the catalysts used for this type of complex reaction, taking into account the challenges facing the catalyst deactivation and reactivation procedures. [ABSTRACT FROM AUTHOR]

The shape and structure engineering of metal oxide nanomaterials are the potential strategies to optimize surface‐active sites with tunable selectivity for heterogeneous catalysis. This work reports the synthesis of two types of nanostructured CeO2–Nb2O5 catalysts: (i) one‐pot hydrothermal synthesis of CeO2–Nb2O5 (CeNb2O5‐HTS, HTS stands for hydrothermal synthesis) and (ii) CeO2 impregnation on hydrothermally synthesized Nb2O5 nanorods (CeNb2O5‐WI, WI stands for wet‐impregnation) to elucidate the role of particle shape and CeO2 addition in the structure–activity efficacy of Nb2O5 nanocatalyst for the selective oxidative C–N coupling of benzyl alcohol with aniline to produce N‐benzylideneaniline (NBA). The characterization studies showed nanorod morphology of Nb2O5 and high dispersion of CeO2 on Nb2O5 nanorods in the CeNb2O5‐WI catalyst with strong acidic sites and more oxygen vacancies. Consequently, a significantly enhanced catalytic activity was achieved with CeNb2O5‐WI nanocatalyst in the coupling of benzyl alcohol and aniline with 96% yield to NBA, whereas 62% conversion of aniline with 92% selectivity to NBA was obtained with pure Nb2O5 nanorods. In contrast, the CeNb2O5‐HTS catalyst gave 37% conversion of aniline only. The versatile efficiency of the CeNb2O5‐WI nanocatalyst is showcased by synthesizing various functional NBA products. The CeNb2O5‐WI catalyst can be recycled 4 times without much variation in NBA selectivity by achieving reasonably good conversion of aniline. [ABSTRACT FROM AUTHOR]

A unique bifunctional catalyst comprised of acid site containing, hierarchical ZSM‐5 (contains acid sites) supported RuCo bimetal, was synthesized using a facile incipient wetness impregnation method. The synergistic interaction between zeolite acid sites and bimetals of this bifunctional material significantly improves its performance as a catalyst of hydrogen producing, dehydrogenation of ammonia borane. [ABSTRACT FROM AUTHOR]

Acidic properties of ion-exchanged LTL zeolites have been studied using FTIR spectroscopy, complemented by X-ray powder diffraction, SEM-EDX, XRF and N2 physisorption. Infrared spectra of the ion-exchanged zeolites show the presence of two intense bands of the bridging OH-groups: a narrow band at ~3640 cm−1 that is attributed to Si(OH)Al groups freely vibrating in 12 MR and a broad, intense band at ~3250 cm−1 that is assigned to bridging OH groups forming hydrogen bond with neighbouring oxygen atoms, e.g., in six-membered rings. The former can be selectively removed by caesium or rubidium cations with up to 3 Cs+ or Rb+ per unit cell readily ion-exchanged into the LTL zeolite, replacing an equivalent number of acidic OH-groups or K+ cations within the structure. The cation migration of the larger cation, evaluated by the Rietveld refinement method, occurs mostly via the main 12 MR channels. By contrast, less than 1 Li+ or Na+ cation per unit cell can be introduced under similar conditions. Accordingly, the concentration of Si(OH)Al groups in back-exchanged NH4-K-LTL with smaller cations (Li+, Na+) does not differ considerably from the concentration of Brønsted acid sites in the original NH4-K-LTL. Lower concentrations of acid sites have been detected in the samples back-exchanged with Cs+, Rb+ and K+. In addition, the acidic properties of NH4-LTL samples have been compared with a structurally related NH4-MAZ zeolite. [ABSTRACT FROM AUTHOR]

Sulfonated carbons and commercial Amberlyst 15 and 45 served as model catalysts to explore the impact of the ratio between stronger and weaker acid sites (NS/NW) on 5‐hydroxymethylfurfural (HMF) and furfural production from fructose and xylose. Catalysts with varying structural and surface properties, and consequently different NS/NW ratios, were prepared from diverse templated mesoporous carbons and distinct sulfonation methods. HMF or furfural yields exhibited an exponential correlation with the NS/NW ratio. However, the catalytic activity per site (TON) displayed a volcano‐like plot, reaching a maximum between NS/NW=2–4. Consequently, our findings suggest the involvement of both strong (sulfonic acid) and weak acid (surface carboxylic acid, alcohol, and phenol groups) sites in monosaccharide dehydration mechanisms. These insights may guide the development of novel catalysts. [ABSTRACT FROM AUTHOR]

A study was carried out on the effect of the nature of the support, composition of the active phase, and heat treatment conditions on the activity of trimetallic Ni‑Co‑Mo catalysts in the hydrotreating of a mixed diesel fraction. Temperature‑programmed desorption was used to show the effect of the amount and strength of the acid sites of the support on the activity of catalysts with the same elemental composition. We established the nickel‑to‑cobalt as well as phosphorus‑to‑molybdenum ratios in these trimetallic hydrotreating catalysts corresponding to the greatest desulfurization and minimum formation of polycyclic aromatic hydrocarbons in the hydrogenate. [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 is considered to be a promising material for NH3-SCR catalysts. However, in practical applications, Cu/SSZ-13 is inevitably exposed to alkali metal deposition. In this paper, Cu/SSZ-13 molecular sieve catalysts were prepared by the ion exchange method, catalysts with different degrees of alkali metal K/Na poisoning were prepared by the wet-impregnation method, and the SCR activity and N2 selectivity of fresh and poisoned catalysts were compared. The effects of alkali ion (Na+ and K+) poisoning on the comprehensive properties of Cu/SSZ-13 were studied. The distribution and quantity of Cu2+ active components in the catalyst before and after poisoning and the change of acidic sites were explored using NH3-TPO, NH3-TPD, H2-TPR, BET, and XRD. The characteristics of crystal structure, specific surface area, and pore structure revealed the influence of the loading of alkali metal K/Na on the adsorption performance, weakened redox characteristics, and a certain degree of structural damage of Cu/SSZ-13 molecular sieve catalyst. It explains that the reason for the decline in catalyst performance after poisoning is due to the decrease in the number of active sites caused by the ion-exchange between alkali metal ions and Cu2+ and H+, the increase of CuxOy species, the decrease of acidic sites, and pore blockage. This provides data support and theoretical basis for the design of highly resistant Cu/SSZ-13 catalysts. [ABSTRACT FROM AUTHOR]

In this paper, MnOx/TiO2 catalysts with different manganese contents were prepared by using vacuum over-impregnation method to support manganese on TiO2 support. However, the activity temperature window was narrow and the denitrification efficiency was only 265–365 °C in the temperature zone above 80%. Therefore, doping W was used to improve the high temperature activity and broaden the activity temperature window. The experimental results show that the active temperature window of the catalyst is expanded to 260–550 °C when doping 20%WO3. The effects of tungsten doping on the structure and surface properties of the catalysts were investigated by XRD, TEM, Raman, XPS, H2-TPR and NH3-TPD. It is found that the increase of manganese content would increase the ratio of Mn4+ and Oα, and then improve the NH3-SCR activity at low temperature. Tungsten doping can provide more strong acid sites and improve the high temperature activity of the catalyst by inhibiting the oxidation of ammonia. [ABSTRACT FROM AUTHOR]

In the process of converting biomass into high value-added chemicals, transfer hydrogenation as a mild hydrogenation method has attracted more and more attention. The catalysts with hydrogenation sites (nano CuNi alloy) and acid sites (Al oxide) highly dispersed on the surface of a stable support (active carbon) were prepared and the importance of acid sites for the activity of CuNi catalysts in transfer hydrogenation was demonstrated. The catalysts showed promising catalytic activity on the transfer hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The CuNi-1Al/AC with 5 wt.% CuNi alloy and 5 wt.% Al got 97.2% GVL yield and 100% LA conversion at 220 ℃ in isopropanol for 2 h. The high activity of the catalyst is attributed to the promoted esterification by the supported acid sites. The Al-modified catalyst also showed activity for esterification reaction in different alcohol hydrogen donors. The catalyst occurs inactive during the cycle due to the shedding of the active components, and the stability of catalyst is effectively improved by a stepwise impregnation. [ABSTRACT FROM AUTHOR]

Herein, four catalysts, consisting of either MFI or BEA as the zeolite framework in the presence or absence of Ni, are compared to explore the individual and collective adsorptive and catalytic contributions of pore topology, Ni sites, and acid sites. Both continuous and pulsed chemisorption/reaction experiments are used to obtain a complete picture of the time‐dependent adsorption‐desorption behavior, reaction mechanisms, and deactivation steps. The methodology highlights the effect of acid sites, especially during the initial stages of reaction and in the BEA‐based catalysts, which have higher acidity at a given Si/Al ratio. In addition, Ni accelerates the reaction and improves the selectivity towards intermediate oligomers. However, the tendency for the most active Ni and acid sites to saturate and deactivate more rapidly than the less active ones may lead to misinterpretation when using the continuous reactor alone. Hence, the dominant mechanisms over the different catalyst sites and reaction times are discussed based on the combined steady and dynamic experiments. [ABSTRACT FROM AUTHOR]

x W/MnCe nanorod catalysts with various tungsten contents were synthesised using the incipient wetness impregnation method for selective catalytic reduction (SCR) of nitrogen oxides with NH 3 (i.e. NH 3 -SCR reaction). Tungsten addition considerably widened the active temperature window and enhanced the SO 2 /H 2 O tolerance of the catalysts. The optimum catalytic performance was achieved when the tungsten content was 15 wt% with NO x conversion being ≥ 80% in the range of 175–450 °C. The MnCe nanorods approximately retained their morphology after tungsten loading. Microcrystalline WO 3 formed when the W content was 15%, resulting in increments in the amount of Ce3+ and Mn4+, which is in favour of the NH 3 -SCR reaction on the catalyst surface. Moreover, the broad active temperature windows of the tungsten-modified MnCe nanorod catalysts were related to the balance between the redox and acidic properties. Tungsten addition enhanced the acidity of the MnCe catalyst while suppressing its reducibility. Both the Brønsted and Lewis acid sites are active, and the formation of reactive bridging nitrate species promote the performance of 15 W/MnCe catalyst. Overall, this study provided an easy method of adjusting the active temperature window of Mn–Ce nanorod catalysts through W modification. [Display omitted] [ABSTRACT FROM AUTHOR]

A range of modified MAZ and LTL zeolites have been prepared and ion-exchanged with a series of alkali metal cations. It has been shown that K, Rb and Cs can be readily introduced into the MAZ structure with ~2 cations ion-exchanged per unit cell. In contrast, less than one cation of Li or Na per unit cell has been introduced under similar conditions. Ion-exchanged zeolites have been characterised using Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, X-ray fluorescence and N2 physisorption in order to gain a better understanding of their structural and acidic properties. The FTIR data indicate considerable heterogeneity of the bridging OH groups in mazzite. The concentration of both Brønsted and Lewis acid sites detected in MAZ using pyridine as a probe molecule is lower than expected from its chemical composition, with the relative accessibility of the bridging OH-groups varying from 16% for H-MAZ to 28% for K-exchanged samples. This is in agreement with the N2 adsorption-desorption data showing a rather low micropore volume for the ion-exchanged materials and with the NH3-TPD results implying considerable transport limitations. This work demonstrates that the channel structure of mazzite is partially blocked resulting in a decreased micropore volume and limited access to the acid sites. [ABSTRACT FROM AUTHOR]

Crystal size is a key parameter of zeolites applied as catalysts. Herein, ZSM-5 crystals with similar physicochemical and acid properties, few defects, and aluminum exclusively in tetrahedral coordination are synthesized and the influence of the crystal size on the MTO and ETA conversion is investigated. Short olefins are the main products of the MTO conversion, whereas larger olefins and aromatics dominate the products after ETA conversion. In the case of both feeds, an increased crystal size decreases the catalyst's lifetime. The MTO conversion over larger ZSM-5 altered the product distribution, which was not the case for the ETA conversion. The reason is that the instantly available aromatics during ETA conversion lead to fast coking and zeolite crystals only active in the outer layers. Thus, the different reactivity of different-sized ZSM-5 is direct proof of a different conversion mechanism for both alcohols. [ABSTRACT FROM AUTHOR]

Acidic properties of ion-exchanged LTL zeolites have been studied using FTIR spectroscopy, complemented by X-ray powder diffraction, SEM-EDX, XRF and N2 physisorption. Infrared spectra of the ion-exchanged zeolites show the presence of two intense bands of the bridging OH-groups: a narrow band at ~3640 cm−1 that is attributed to Si(OH)Al groups freely vibrating in 12 MR and a broad, intense band at ~3250 cm−1 that is assigned to bridging OH groups forming hydrogen bond with neighbouring oxygen atoms, e.g., in six-membered rings. The former can be selectively removed by caesium or rubidium cations with up to 3 Cs+ or Rb+ per unit cell readily ion-exchanged into the LTL zeolite, replacing an equivalent number of acidic OH-groups or K+ cations within the structure. The cation migration of the larger cation, evaluated by the Rietveld refinement method, occurs mostly via the main 12 MR channels. By contrast, less than 1 Li+ or Na+ cation per unit cell can be introduced under similar conditions. Accordingly, the concentration of Si(OH)Al groups in back-exchanged NH4-K-LTL with smaller cations (Li+, Na+) does not differ considerably from the concentration of Brønsted acid sites in the original NH4-K-LTL. Lower concentrations of acid sites have been detected in the samples back-exchanged with Cs+, Rb+ and K+. In addition, the acidic properties of NH4-LTL samples have been compared with a structurally related NH4-MAZ zeolite.

[Display omitted] • Cu+ species could adsorb C O bonds and enhance C O bond hydrogenation. • Cu0 species were the main active sites for 2-propanol dehydrogenation. • Synergistic effect between CoO x acid and Cu metal sites promoted the HDO reaction. • Cu/CoO x catalysts showed universality for the HDO of biomass derivatives. The efficient hydrodeoxygenation (HDO) of biomass derivatives to yield specific products is a significant yet challenging task. In the present study, a Cu/CoO x catalyst was synthesized using a facile co-precipitation method, and subsequently used for the HDO of biomass derivatives. Under optimal reaction conditions, the conversion of 5-hydroxymethylfurfural reached 100% with a selectivity of ∼99% to 2,5-diformylfuran. In combination with the experimental results, systematic characterizations revealed that CoO x , as the acid site, tended to adsorb C O bonds, and the metal sites of Cu+ were inclined to adsorb C O bonds and enhance C O bond hydrogenation. Meanwhile, Cu0 was the main active site for 2-propanol dehydrogenation. The excellent catalytic performance could be attributed to the synergistic effects of Cu and CoO x. Further, by optimizing the ratio of Cu to CoO x , the Cu/CoO x catalysts exhibited notable performance in HDO of acetophenone, levulinic acid, and furfural, which verified the universality of the catalysts in the HDO of biomass derivatives. [ABSTRACT FROM AUTHOR]

Although the surface acidity of CeO2 has been increased by H2SO4 to increase its acid sites, the low-temperature (<250 °C) activity of sulfated CeO2 catalysts still needs to be improved. In this study, a Pt-modified CeO2 catalyst was prepared by impregnation or reduction methods to increase its catalytic activity. The results showed the Pt-modified CeO2 catalyst significantly widened its low-temperature catalytic window. The NO conversion and N2 selectivity of the Pt1.0%/SCe-I sample were both more than 90% at 200–350 °C because of its numerous acid sites, excellent redox ability, and higher Pt2+ content. NH3, NH4+, –NH2, and bridging nitrates and monodentate nitrates on the Pt1.0%/SCe-I catalyst surface acted as the active substances. Among them, coordinated NH3 at the Lewis acid sites reacted first. This study highlights the interactions among metals, sulfates, and carriers and supplies a useful method to improve the low-temperature activity of sulfated CeO2. [ABSTRACT FROM AUTHOR]

There is a huge rise in the demand of plastics; as a result, plastic waste gets accumulated by improper disposal methods and degrades the living environment. Despite recycling of plastic waste, majority of it ends up in landfills, disposed in oceans and rivers. More researches are looking at better solution and development of integrated plan to handle plastic waste. The current review aims to detail the routes of plastic waste management, through thermal, catalytic and microwave pyrolysis. The effect of operating parameters such as temperature, time, types of feedstocks and product yield is discussed under thermal pyrolysis. The urge to develop a sustainable catalyst incorporating acid sites, enhanced catalytic activity and resistive to coke development was more focussed in this study. In microwave pyrolysis, the use of biomass as absorbents and the challenges faced during microwave pyrolysis are deeply reviewed in this article. [ABSTRACT FROM AUTHOR]

The study investigates adsorption of chicken egg lysozyme and bovine serum albumin over BEA zeolites synthesized in alkaline and fluoride media. The protein adsorption value achieved on the samples synthesized in the alkaline medium was higher. An evaluation of the surface areas occupied by protein molecules showed that only a portion of the external surface was involved in the adsorption. The protein adsorption reduced the concentration of acid sites in the zeolite samples. [ABSTRACT FROM AUTHOR]

MCM-41, based on the size and arrangement of pore structure, can be a good option as a support for homogenous catalyst. In the present work, in order to overcome the low acidity of MCM-41 and obtain a bifunctional catalyst with modulated acidity in the aspect of amount, strength, and type of Lewis and Brønsted acid sites, a complex of Schiff base thiosemicarbazone (TSC) with copper (II), and zinc (II) metals, and amino acid (L-Histidine) as a secondary ligand was functionalized on it (M-H-L@MCM-41). The results of Fourier Transform Infrared Spectrometer (FT-IR), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller Theory (BET), Field-Emission Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Diffuse Reflectance Spectroscopy (DRS), UV-vis Spectrophotometer (UV-Vis), Thermal Gravimetric Analysis (TGA), and Thermal Program Desorption (NH3-TPD) analysis confirmed the complex was successfully immobilized on the MCM-41. In addition, NH3-TPD technique confirm the presence of strong acid sites and moderate participation of medium acid sites in the formulated catalyst. This heterogeneous acidic catalyst can be used as an efficient, stable, easy removal, reusable, and eco-friendly catalyst for the synthesis of dihydropyridine derivatives (DHPMs) through Biginelli reaction. [ABSTRACT FROM AUTHOR]

ZSM-5 zeolite is the synthetic counterpart to mutinaite. After thermal activation of the as-synthesized form, the symmetry of the ZSM-5 zeolite is lowered to the monoclinic P21/n. ZSM-5 then undergoes a polymorphic displacive phase transition from the monoclinic P21/n to the orthorhombic Pnma, Pn21a or P212121 space groups, which occurs upon heating. This phase transition can be influenced by factors such as the type and amount of sorbate molecules present in the zeolite channels. ZSM-5 has many applications, including as a catalyst or sorbent in various industries, where high thermal stability is required. In this study, four ZSM-5 zeolites with different Si/Al ratios were investigated by synchrotron X-ray powder diffraction at both room temperature and high temperature conditions to determine the effects of chemical composition on the structural response of the zeolite lattice. The results showed that the ZSM-5 zeolites retained their crystallinity and structural features throughout the thermal treatment, indicating that they could be used as effective acid catalysts. Distortions in the zeolite framework can occur after TPA+ decomposition and thermal activation, affecting thermal regeneration and efficiency. The charge balance in ZSM-5 is achieved by the formation of Brønsted acid sites, and variations in bonding geometries are influenced by the initial Si/Al ratio. [ABSTRACT FROM AUTHOR]

In this study, different solid acids were used as catalysts for demethylation of model compound 2-methoxy-4-methylphenol (creosol) to produce 4-methylcatechol (4-MeCat) in halogen-free aqueous system. The results showed that a high 4-MeCat yield of 48.5% was achieved over TiO2 supported on activated carbon, while the Nb2O5 catalyst with suitable Brønsted/Lewis acid site exhibited the highest average production rate of 0.053 min−1. The high total acidity improves the 4-MeCat yield and a suitable ratio of Brønsted to Lewis acid sites benefits the catalytic activity over unit acid sites. The stable crystal and acid sites of Nb2O5 catalyst result in high activity stability, while the supported TiO2 catalyst is deactivated much faster. The loss of acid sites and acid site coverage are the main deactivation reasons for demethylation in aqueous medium. [ABSTRACT FROM AUTHOR]

Link for citation: Nazarova G.Y., Ivashkina E.N., Maltsev V.V. Calculation of thermodynamic and kinetic parameters of catalytic cracking reactions on Lewis and Brønsted acid sites. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 214-225. In Rus. The relevance of the research is caused by the emerging necessity of developing a mathematical model to optimize the heterogeneous process of catalytic cracking. This tools should take into account both the chemical transformations of a wide range of hydrocarbon groups (different feedstock types), as well as the stages of adsorption, reactants diffusion, conversion of hydrocarbons on the catalyst surface, acid characteristics and pore size of the catalysts. The study of the hydrocarbon conversion patterns on Lewis or Brønsted acid sites using quantum-chemical modeling methods allow us to quantify the thermodynamic parameters of reactants adsorption, the kinetic parameters of carbocations formation and cracking on acid sites. These results are necessary to develop a mathematical model based on the of heterogeneous catalytic reaction mechanism. The aim of this work is to identify the level of quantum chemical theory and to determine the thermodynamic and kinetic parameters of reactants adsorption, carbenium ions formationand hydrocarbons cracking on Lewis and Brønsted acid sites. Methods: quantum-chemical modeling methods to optimize the molecular geometry of reactants and products of catalytic cracking reactions, calculate vibrational frequencies, thermodynamic parameters of adsorption and catalytic cracking of hydrocarbons and heteroatomic compounds with the participation of Bronsted and Lewis acid sites. Results. The chosen level of quantum-chemical theory allowed obtaining the results that are consistent with the laws of the process and the experimental reactivity of hydrocarbons in cracking reactions on acid catalysts. The thermodynamic parameters of the adsorption of C6–C16 hydrocarbons and thiophenes on Lewis and Brønsted acid sites were identified. We found that during the cracking of n-hexane on the Lewis acid site, the reaction is limited by the carbenium ion formation stage.The activation energy of this stage was 281,3 kJ/mol whereas the value for the cracking stage was 277,2 kJ/mol. Further study shows that the activation energy of carbenium ion formation from izohexane and C8–C10 alkanes with normal structure on the Lewis acid site was 257,6 and 279,2…277,9 kJ/mol. The most energetically favorable is the formation of carbocation from hexene at Brønsted acid sites (76,59 kJ/mol). The results of the work will be used to create a mathematical model of a heterogeneous process based on the Langmuir–Hinshelwood equations.

The adsorption and photocatalytic activity of iron-containing metal-ceramic composites produced by the selfpropagating combustion of aluminum ferrosilicon in nitrogen with the addition of metallic tantalum (0, 5, 10, 15 wt.%) during oxidative degradation of pharmaceutical pollutants (chloramphenicol, metamizole, cinnarizine) under UV and visible light was evaluated. The phase composition of the composite materials was determined by X-ray diffraction and infrared spectroscopy. The morphological features and optical properties of the composites were investigated, and the band gaps of the semiconductors included in the ceramic matrix were determined. The acid properties of the surface of the composites were studied using pH-metry and the Hammett indicator. The correlation of the number of surface-active sites and adsorption of pollutants with the corresponding value of pКa was shown, and the mechanisms of adsorption were proposed. Optimal conditions for the oxidative degradation of chloramphenicol (~100%) under visible light were found: a composite (5% Ta) with the addition of H2O2 to combine heterogeneous catalysis with the homogeneous photo-Fenton system. [ABSTRACT FROM AUTHOR]

[Display omitted] • The NO conversion of the Cr:Zr:Ce = 8:2:1 catalyst reached 90 % with 500 ppm SO 2 and 85 % with 1000 ppm SO 2 for 20 h. • Interactions among the CrO x , ZrO x , and CeO x influenced catalyst surface acidity and adsorption species through solid solution formation. • CeO x species primarily served as acid sites rather than redox sites in the CrZrCeO x , acting as sacrificial sites to protect CrO x active sites by minimizing the formation of Cr sulfates. • Langmuir-Hinshelwood mechanism was on the CrZrCeO x with nitrites, chelated bidentate nitrates and NH 3 * adsorbed on Lewis acid sites as the major active species. This paper mainly talked about acid sites-CeO x doping CrZrCeO x catalyst with high SO 2 resistance for marine NH 3 – SCR (selective catalytic reduction). The NO removal efficiency of the Cr:Zr:Ce = 8:2:1 catalyst reached 90 % with 500 ppm SO 2 and 85 % with 1000 ppm SO 2 for 20 h, respectively. It was inferred that the main roles of CeO x species were acid sites but not redox sites. CeO x addition promoted the SCR performance and SO 2 resistance, which significantly changed the adsorbed species on the surface. CeO x acted as sacrifice sites to protect CrO x actives sites through reducing the combination of Cr and sulfates. The Cr:Zr:Ce = 8:2:1 catalyst followed Langmuir-Hinshelwood (L-H) mechanism and the reaction process was derived in this paper. It indicated that the Cr:Zr:Ce = 8:2:1 catalyst would be a promising marine SCR catalyst with good SO 2 resistance in the future. [ABSTRACT FROM AUTHOR]

The introduction of solid acid sites can effectively increase the activity and hydrothermal stability of the FeTi catalyst due to the formation of the structure P-O-Fe/W-O-Fe. [Display omitted] • PO 4 3- and WO 3 doping enhances the SCR performances of the FeTi catalyst. • The SCR catalytic reaction is primarily governed by the E-R mechanism. • The P-O-Fe/W-O-Fe structure increases the hydrothermal stability of catalyst. • PO 4 3- can still exist stably after hydrothermal treatment. Acid sites and redox sites with high thermal stability are crucial for the NH 3 -SCR catalyst for diesel vehicles. The surface acidity of FeTi catalysts is improved by modified with the solid acid of PO 4 3- or WO 3. The acid-modified FeTi catalysts show superior NH 3 -SCR activity hydrothermal stability with a wide temperature window. The introduction of acid groups not only provides a large number of Brønsted acid sites but also promotes high dispersion of the active species of redox sites due to the formation of the structure P-O-Fe/W-O-Fe. The P-O-Fe/W-O-Fe structure can also improve the redox properties of the FeTi catalysts and inhibit the phase transformation of the TiO 2 support during high-temperature hydrothermal process. The reaction kinetics indicate that the reaction rate is primarily related to the concentration of NO. The mechanistic study indicates that the catalytic reaction is primarily governed by the Eley-Rideal mechanism. [ABSTRACT FROM AUTHOR]

Synopsis: This study provides a new insight into the designing of MoTiO x catalysts with improved alkali resistance by loading Fe 2 O 3. [Display omitted] • The loading of 20 wt% Fe 2 O 3 significantly improved catalyst SCR activity and anti-alkali properties of MoTiO x catalyst. • Fe 2 O 3 -MoTiO x has better anti-alkaline properties compared to traditional commercial V 2 O 5 -WO 3 -TiO 2 catalysts. • Fe 2 O 3 loaded catalysts are easier to combine with Ti species, Fe-Ti has a certain synergy, common alkali resistance, Mo species are retained to participate in SCR reaction. Catalyst is the core of selective catalytic reduction (SCR) technology, and an ideal SCR technology requires that the catalyst should have high activity and resistance to alkali metal poisoning. Therefore, in this paper, the influence of Na poisoning on the catalytic performance of Fe 2 O 3 -MoTiO x catalysts in the selective catalytic reduction (SCR) reaction was investigated, and the anti-alkali mechanism was revealed. The Fe 2 O 3 -MoTiO x catalyst demonstrated the NO conversion was 90 % at a broad temperature range of 225-400 °C when the Fe 2 O 3 loading ratio was 20 wt%. Besides, 80 % NO conversion rate of the Fe 2 O 3 -MoTiO x catalyst at 320 °C was still achieved even at a Na+ concentration of 300 μmol g-1. The phenomenon was attributed to the interaction between Fe and Ti species, which could generate more Lewis acid centers and facilitate the adsorption activation of NH 3. During the Na poisoning process, Na ions predominantly adsorbed on the Fe 2 O 3 , effectively safeguarding the MoTiO x catalyst. Additionally, although the Brønsted acid sites were deteriorated because of Na poisoning, the abundant Lewis acid sites were preserved for NH x adsorption. Therefore, the Na-poisoned Fe 2 O 3 -MoTiO x catalyst maintained efficient NH 3 adsorption and NO activation. The work provided theoretical guidance and data support for the development of novel alkali-resistant SCR catalysts. [ABSTRACT FROM AUTHOR]

Utilizing MIL-100(Fe) as the precursor, Fe-based catalysts were developed for NH 3 -SCR, which served as the matrix to incorporate acidic promoters, phosphotungstic acid (HPW) through hydrothermal (HT), impregnation (IM), and grinding (GR). The HT-prepared HPW-FeO x(MOFs) -HT outperformed others, achieving over 90 % NO x conversion across 205–470 °C and maintaining similar activity even with 5 vol% H 2 O presents. This method fostered a beneficial interaction between W and Fe, leading to the formation of γ-Fe 2 O 3 and an increase in active oxygen species, which enhanced NO adsorption and activation for faster SCR. Over HPW-FeO x(MOFs) -HT, NH 3 -TPD analysis confirmed HPW's role in augmenting the total acidic site along with promoting the reactivity of NH 3 adsorbed at Lewis acidic site at low temperature, demonstrating the catalyst's high-temperature SCR efficacy through strategic molecular and structural optimization. [Display omitted] • Developed Fe-based catalysts from MOFs and modified with HPW. • HPW-FeOx (MOFs) -HT achieved over 90 % NO x conversion across 205–470°C. • Enhanced catalyst acidic properties after HPW introduction via hydrothermal. • Strong interaction between Fe and W led to the formation of stable γ-Fe 2 O 3. • Incorporating W promoted the formation and mobility of active oxygen species. [ABSTRACT FROM AUTHOR]

Encapsulation of metal oxide nanoparticles is a common strategy to improve the catalytic performance of zeolite catalysts. However, the unsuitable pore size and Lewis/Brönsted acid ratio of zeolite-confined catalysts are not conducive to the reactant contact. Herein, a simple in-situ encapsulation strategy for one-step Al doping, mesoporous construction and encapsulation of CeO 2 nanoparticles in MFI zeolite (CeO 2 @ZSM-5) is achieved by recrystallization of silicalite-1. The DFT results indicate that Al doping improves the electron transfer to enhance the in situ encapsulation effect and dispersion of CeO 2 particles and the preliminary adsorption performance for o -DCB. The meso-ZSM-5 improved the mass transfer efficiency and accessibility of active sites. Thus, CeO 2 @ZSM-5 exhibited exceptional o-dichlorobenzene oxidation performance (T 90 = 340 °C) and anti-poisoning ability. The reaction mechanism of CeO 2 @ZSM-5 based on surface oxygen species and lattice oxygen was proposed. This study provides a promising strategy for the design of intra-mesopore confined metal oxide nanoparticles catalysts. [Display omitted] • One-step doped Al and CeO 2 nanoparticles encapsulation in meso-ZSM-5 by re-crystallization silicalite-1. • Doped-Al enhances the in-situ encapsulation effect, Brönsted acid ratio and the o-DCB preliminary adsorption. • The meso-ZSM-5 improves the mass transfer efficiency and accessibility of active sites. [ABSTRACT FROM AUTHOR]

• Well-defined crystal contributed to the formation of Fe-O-Ce after sulfidation. • Redox capability of S-CP-Fe-Ce could be improved by sulfidation. • Generation of Brönsted acid sites enhanced the activation of NH 3 -adsorption. • NH 3 -SCR reaction over S-CP-Fe-Ce involved E-R and l -H mechanisms. Fe-Ce catalysts were prepared and then sulfated with SO 2 in the selective catalytic reduction of NO by NH 3. S-CP-Fe-Ce with precipitation method exhibited the highest activity, which is due to large specific surface area, the abundance of oxygen vacancies as well as the formation of Fe-O-Ce structure, thus contributing to the strong redox capacity. Furthermore, sulfates on S-CP-Fe-Ce facilitate the conversion of Lewis acid sites to Brönsted acid sites, and promote the transformation of low-active nitrates to highly active nitrates, which is crucial for enhancing its activity. Besides, NH 3 adsorbed over S-CP-Fe-Ce easily undergoes oxidation and dehydrogenation to form -NH 2 , which further reacts with gaseous NO, causing the superior catalytic performance. Additionally, NO was activated to form highly active monodentate nitrate and cis-N 2 O 2 2-, enabling the rapid reaction with NH 3 , leading to the outstanding the catalytic activity. The NH 3 -SCR reaction of S-CP-Fe-Ce simultaneously involves E-R and l -H mechanisms. [Display omitted] Fe-Ce catalysts modified by SO 2 were investigated in the selective catalytic reduction reaction. The formation of Fe-O-Ce structure, the excellent redox ability and the abundance of Brönsted acid sites could improve the adsorption of NH 3 , and promoted the formation of more highly active nitrate species, resulting in the improvement of catalytic activity in the NH 3 -SCR reaction. [ABSTRACT FROM AUTHOR]

Mordenites are widely used in catalysis and environmental protection. The catalytic properties of mordenite are largely determined by the composition of its crystal framework, i.e., the SiO2/Al2O3 molar ratio (MR), and the cationic form. In H-mordenites, the most important characteristic becomes the structure and distribution of acid sites, which depends on the number and distribution of Al tetrahedra in the framework. In the present work, the local structure of these centers in H-mordenite catalysts with a nominal MR varied from 9.9 to 19.8 was studied in detail using a combination of magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectroscopy (FTIR). 27Al MAS NMR indicates the presence of extra-framework Al in most of the studied samples that results in a higher real MR of the zeolitic framework compared to the nominal value. Concentrations of Lewis and Brønsted acid sites, as well as of silanol groups were estimated by elemental analysis, NMR, and FTIR spectroscopy. The values of site concentrations obtained from band intensities of adsorbed CO and those of OH groups are compared with the amount of framework and extra-framework aluminum. The advantages and restrictions of different methods of active site characterization are discussed. [ABSTRACT FROM AUTHOR]

Herein, we report the function of copper sites in Cu-SSZ-13, Cu-ZSM-5 and Cu-Beta catalysts with the same Si/Al ratio (14) and Cu/Al ratio (0.4) on selective catalytic reduction of NO with NH3 (NH3-SCR) and reveal the relationship between active sites (Cu sites, acid sites) and catalytic activity. The results show that the amount of isolated Cu2+ ions in the catalysts directly determines the formation of strong Lewis acid sites and reaction intermediate NO3− ions, thus affecting the low-temperature SCR performance, while the amount of highly stable Cu+ ions and Brønsted acid sites is related to the high-temperature SCR performance of the catalysts. Consequently, it contains enough isolated Cu2+ ions, highly stable Cu+ ions and Brønsted acid sites, which endows Cu-SSZ-13 with excellent NH3-SCR activity. [ABSTRACT FROM AUTHOR]

Solid-state NMR (ssNMR) spectroscopy is a powerful technique for characterizing the surface sites of solid acids and organic intermediates formed during the acid catalyzed reaction. As a very useful probe molecule, ammonia is often utilized to determine the density of solidacids’ surface sites by ssNMR spectroscopy. The present mini-review summarizes some of the latest research developments on the quantitative characterization of the acid sites and carbenium ions during the zeolite catalytic reaction by ammonia probe-assisted ssNMR spectroscopy.

Micro-mesoporous aluminosilicates based on ZSM-5 zeolite, obtained by a dual template method, as well as in the presence of a dual-functional template (i.e. a Gemini-type surfactant), were tested in the oxidation of furfural with hydrogen peroxide. Even substantial changes in acidity and porosity of the catalysts result in minor variations of selectivity towards the desired products. Application of the synthesized zeolite-based materials in the oxidation of furfural with hydrogen peroxide leads to formation of 2(5H)-furanone (yield up to 28.5%) and succinic acid (up to 19.5%) as the main C4 reaction products. The kinetic model developed previously to treat the results for oxidation of furfural over sulfated zirconia was able to describe the data also for micro-mesoporous aluminosilicates. [ABSTRACT FROM AUTHOR]

[Display omitted] Due to the accumulation of heavy metal compounds produced by the sintering process in steel industry, the catalysts used for low-temperature selective catalytic reduction of NO with NH 3 (NH 3 -SCR) might be seriously deactivated. In this work, the deactivation effect of PbCl 2 , Pb(NO 3) 2 , and PbSO 4 on Mn-Ce activated carbon supported catalyst for low-temperature NH 3 -SCR of NO was investigated and compared. Poisoned catalysts were provided by impregnating fresh catalysts with Pb(NO 3) 2 , PbSO 4 and PbCl 2 aqueous solutions, respectively. Deactivation could be observed on the poisoned samples, and the deactivation degree was following PbCl 2 > PbSO 4 > Pb(NO 3) 2. The catalytic activities of all samples were tested, and the physicochemical properties of fresh and poisoned catalysts were assessed. PbCl 2 caused the most severe deactivation of the catalyst, owing to its poor redox property and surface acidity. Cl- could also react with Mn active sites to form -O-Mn-Cl bonds, resulting in additional acid sites, although these newly generated sites were not reactive in NH 3 -SCR reaction process. PbSO 4 exhibited moderate poisoning effect due to the addition of SO 4 2-, which created new Brønsted acid sites, facilitating the NH 3 adsorption and NO reduction. Pb(NO 3) 2 had the least poisoning impact on the catalyst due to the NO 3 –, promoting the NH 3 activation. The in situ DRIFTS results revealed that NH 3 -SCR reaction over all samples was governed by Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism, and did not change due to the lead poisoning. Finally, a possible mechanistic model for different lead salts poisoning over Mn-Ce/AC catalyst was proposed. [ABSTRACT FROM AUTHOR]

ZSM-5 zeolite is the synthetic counterpart to mutinaite. After thermal activation of the as-synthesized form, the symmetry of the ZSM-5 zeolite is lowered to the monoclinic P21/n. ZSM-5 then undergoes a polymorphic displacive phase transition from the monoclinic P21/n to the orthorhombic Pnma, Pn21a or P212121 space groups, which occurs upon heating. This phase transition can be influenced by factors such as the type and amount of sorbate molecules present in the zeolite channels. ZSM-5 has many applications, including as a catalyst or sorbent in various industries, where high thermal stability is required. In this study, four ZSM-5 zeolites with different Si/Al ratios were investigated by synchrotron X-ray powder diffraction at both room temperature and high temperature conditions to determine the effects of chemical composition on the structural response of the zeolite lattice. The results showed that the ZSM-5 zeolites retained their crystallinity and structural features throughout the thermal treatment, indicating that they could be used as effective acid catalysts. Distortions in the zeolite framework can occur after TPA+ decomposition and thermal activation, affecting thermal regeneration and efficiency. The charge balance in ZSM-5 is achieved by the formation of Brønsted acid sites, and variations in bonding geometries are influenced by the initial Si/Al ratio.

[Display omitted] • M−x and MT-0.1 were synthesized by acid treatment in the presence and absence of templates. • Acid treatment increased the specific surface area and pore structures of samples, and selectively passivated the Brønsted acid sites in 12-MR, thereby promoting mass transfer and reducing carbon deposition. • The use of CHA template molecules can protect the Brønsted acid sites in 8-MR from the effects of acid treatment to some extent. • The DME conversion and MA selectivity of M−0.1 were significantly promoted compared to M−0. A series of mordenite zeolites were prepared by a simple acid treatment in the presence and absence of templates for dimethyl ether carbonylation to methyl acetate. The structure and acidity of the prepared catalysts were characterized by XRD, BET, SEM, NH 3 -TPD, FTIR and TG. The nitric acid treatment mainly removed non-framework Al atoms in zeolites, thereby improving the crystallinity of samples, which was also protected by the template. Also, the specific surface area and mass transfer were improved due to the increase in porous structure and surface roughness. Furthermore, compared to 8-MR, the Brønsted acid sites in 12-MR can be reduced to a greater extent. And the protective effect of template molecules on the Al atom can maintain a relatively high level of Brønsted acid sites in mordenite. The relatively high Brønsted acid sites in 8-MR served as active sites. Meanwhile, the significant reduction of Brønsted acid content within 12-MR effectively inhibited carbon accumulation and improved the stability of the carbonylation reaction. M-0.1 exhibited the best catalytic performance, with DME conversion rate and MA selectivity of 72.75% and 96.14%, respectively. Therefore, retention of the organic template during acid treatment is an effective approach to improve the carbonylation activity. [ABSTRACT FROM AUTHOR]

Sulfur poisoning is a major challenge in the design of high-performance heterogeneous catalysts. In this study, an effective sulfur-resistant catalyst for the catalytic decomposition of CH 3 SH was prepared by a secondary crystallization method. Compared with the conventional impregnation method, this method can effectively regulate the position of Fe on the S-1 support and the property of the acidic site. The strong redox properties, strong acidity and highly dispersed Fe species on the modified 2.5 % Fe@S-1 catalyst contributed to the improvement of the low-temperature activity of the catalytic decomposition of CH 3 SH, and increased the sulfur and coke resistantce of the catalyst. As expected, the 2.5 % Fe@S-1 catalyst maintained 90 % CH 3 SH conversion within 80 h of TOS. By contrast, Fe particles in 2.5 % Fe/S-1 catalysts was large and prone to agglomeration, resulting in poor catalyst stability. It was shown that Fe-based catalysts prepared by the secondary crystallization method have potential applications in CH 3 SH degradation. [Display omitted] • Dispersion and acidity of Fe-based catalysts are well modulated with secondary crystallization. • The formation of framework iron limits the aggregation of Fe particles. • The obtained Fe@S-1 catalysts show excellent sulfur-resistance towards CH 3 SH decomposition. [ABSTRACT FROM AUTHOR]

In this study, tin oxide (SnO 2), molybdenum oxide (MoO 3) and a mixed oxide based on tin and molybdenum (respectively, Sn100, Mo100 and SnMo25, synthesized by the impregnation method) were applied in xylose conversion. The best results were obtained employing Mo100 and SnMo25. In the presence of SnMo25, after 0.5 h, xylose conversions of 39.5%, 34.1% and 63.4% were obtained, respectively, at 110, 130 and 150 °C. For Mo100, conversions of 49.6%, 71.8% and 85.3% were attained under the same reaction conditions, showing that Mo100 provided the best conversion results. However, with the use of this catalyst there was an increase in the amount of soluble and insoluble polymeric material. In terms of the soluble products formed from xylose, depending on the reaction condition were detected xylulose (X), lyxose (L) and furfural (FUR), glyceraldehyde (GL), pyruvaldehyde (PYR), glycoaldehyde (GLYC), dihydroxyacetone (DHA), lactic acid (AL), levulinic acid (LA) and acetic acid (AA). However, with the use of Sn100 or without a catalyst (systems with low conversions) there was mainly the formation of lyxose. The use of Mo100 and SnMo25 (systems which exhibit high acidity) leads mainly to isomerization, epimerization and dehydration reactions, as in the case of the retro-aldol pathway and furfural conversion, highlighting the importance of Lewis and Bronsted acid sites in relation to modulating the selectivity of the systems. [Display omitted] • Individual and mixed metal oxide of tin and molybdenum were synthesized. • Catalysts were applied in xylose conversion. • Mo100 and SnMo25 lead to best xylose conversion. • Lewis and Bronsted acid sites can modulate the selectivity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydrogenation of polycyclic aromatic hydrocarbons to saturate all rings is of great importance for hydrogen storage and fuel production, which is extremely hard due to the hardly broken π bond. In this work, various bifunctional catalysts of HY zeolite supported Pd (Pd/HY) are prepared by a facile impregnation method for hydrogenation saturation of naphthalene. The system of Pd/HY is finely tuned by changing the SiO 2 /Al 2 O 3 ratio and mesopore volume of HY. The influences of active metal, acid sites and mesopores on the catalytic performance are revealed. A factor termed mesopore-acid-metal factor (X) is defined to comprehensively and quantitatively describe the states of mesopores, acid sites, and Pd NPs in the Pd/HY catalyst. In our catalytic system, X correlates the yield of decalin well with a R2 value of 96.03%. The quantitative structure-activity relationship of the Pd/HY system has been determined. By balancing the mesopores, acid sites and Pd state, high decalin yield and good stability have been achieved. In addition, the kinetic behaviors of naphthalene hydrogenation on the optimal catalyst are preliminarily investigated and the apparent activation energy for the formation of tetralin is calculated to be 61.64 kJ/mol. [Display omitted] • Active and stable Pd/HY prepared by a facile excess impregnation method. • A mesopore-acid-metal factor (X) for comprehensively describing the catalyst state. • Quantitative correlation between activity and structure of Pd/HY. • Efficient deep hydrogenation saturation on well-balanced Pd/HY-9.5. • Kinetic analysis on the hydrosaturation of naphthalene catalyzed by Pd/HY-9.5. [ABSTRACT FROM AUTHOR]

Pd/Al2O3 catalysts modified by different chemical elements (Mg, Si, Ce, and Zr) were tested for methane (CH4) catalytic combustion, and PdO nanoparticles loaded on modified Al2O3 were systematically studied. These conditions assess the carrier effects of Pd/Al2O3 and acid strength influences on CH4 combustion. We observed carrier effects on activation energy through tuning Pd 3d binding energies (BEs) and on pre-exponential factors (A) through Pd dispersion and acidity on supports. When the BE of Pd 3d5/2 is 337.3 eV, PdO nanoparticles loaded on modified Al2O3 have excellent activity in cracking the C−H bond of CH4, which leads to the lowest activation energy (Ea), regardless of the size effect of the PdO nanoparticle. Furthermore, a theoretical construction that acid sites on catalysts promote the reversible elementary step (2Pd−OH ↔ Pd−O* + Pd* + H2O) right shifts improving the A dependency on the quantity of exposed Pd* and Pd−O*. As a result, Al2O3, as the carrier, not only modifies the electronic characteristics and size of supported PdO nanoparticles but also participates in the reaction process via acid sites on the surface of Al2O3.