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Au-Beta zeolites prepared by different methods and on supports of different compositions were studied in base-free glucose oxidation to gluconic acid. The catalysts were characterized by XRD, N2 adsorption/desorption, TEM, UV–vis and FTIR spectroscopy, ICP-OES and pyridine adsorption combined with FTIR measurements in order to estimate the structural/textural and surface properties of prepared materials and their impact on the activity and selectivity in glucose oxidation. A relationship between the gold particle size, depending on the method of gold deposition, and the effectiveness of glucose oxidation to gluconic acid, expressed by glucose conversion and the selectivity to gluconic acid, was observed. The optimal average gold nanoparticles (NPs) size corresponding to the maximum glucose conversion was ∼6 nm, whereas the normalization of structure/size sensitivity to exposed surface gold atoms (TOF) moved this optimum to Au NPs of ca. 24 nm. The presence of niobium in the support reduced the gold particle size, decreased the activity in glucose oxidation and affected the selectivity of the reaction, enhancing glucuronic acid formation. Addition of cerium dopant to the zeolite support for gold resulted in an increase in glucose conversion and stabilization of the catalyst activity for six investigated reaction cycles. Deactivation of the catalysts in successive reaction runs depended on the method of gold deposition and the type of zeolite support.

Mesoporous silicas, SBA-15, synthesized with the addition of zirconium oxychloride (ZrOCl2) which ensures obtaining short channels, were used as supports for metallic modifiers including silver, copper, gold and iron. Different preparation routes of these materials, denoted as SBA-S (S stands for short channels), resulted in different morphologies and different contents of zirconium left after the preparation. Samples SBA-S1 and SBA-S2 were obtained after treatment with sulfuric acid (leaching of ca. 98.5% of zirconium ions), whereas SBA-S3 was not treated with H2SO4, which resulted in a higher zirconium content. Metallic catalysts were prepared by grafting of metal species on organosilane functionalized supports. Characterizations by X-ray diffraction, ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy allowed determination of the oxidation state of metallic modifiers and evidenced the interactions between the modifier (Ag, Au, Cu, Fe) and the zirconium that remained in the silica support. The reaction of 2-propanol decomposition and Fourier-transform infrared spectroscopy combined with adsorption of pyridine clearly showed the effect of zirconium on surface properties of metallic catalysts. Strong acidic Zr4+ species modified the surface acidic-basic properties of the catalysts. This phenomenon should be taken into account when the SBA-S materials are used as supports for potential catalytic applications. The reference material was the long channel SBA-15 (denoted as SBA-L) prepared and modified with metals by the same routes as the short channel materials.

Two different supports containing zinc (ZnO and Zn/SBA-15) were used to prepare mono- and bimetallic gold, silver and gold-silver catalysts. Zinc was used for two different purposes in these materials: (i) as a support in the form of zinc oxide and (ii) as a dopant introduced to short-channel SBA-15 by wetness impregnation. Short channel SBA-15 was used as the reference support. The materials obtained were characterized by: N2 physisorption, XRD, TEM, UV–vis, XPS, XAS and their activity was tested in the reactions of propene and methanol oxidation in the gas phase. The state of metals (Au, Ag, Zn) and the composition of gold-silver alloy formed on the catalysts surface were considered in terms of thermal activation of catalysts in inert gas and in hydrogen flow as well as interaction with reagents and products of methanol and propene oxidation. It was found that silver species were responsible for the activity in propene oxidation and its total combustion to CO2, whereas (Au0)δ− metallic particles were active in methanol oxidation. Selectivity to acrolein in propene oxidation was achieved thanks to the presence of Au-Ag alloy whose composition depended on the presence of zinc oxide and activation conditions. The alloy was not stable and separated into metals upon propene oxidation conditions. In methanol oxidation, zinc species took part in selective oxidation to methyl formate.

Gold and copper were supported on short-channel SBA-15 and conventional long-channel SBA-15 for selective oxidation of propene with molecular oxygen. The obtained materials were characterized by several techniques (N2 adsorption, XRD, UV–vis, XPS, XAS) and tested as catalysts in propene oxidation with molecular oxygen. The influence of the following parameters on the catalytic activity and the product selectivity to acrolein was considered: i) the length of channels in SBA-15 which determined the particle size of active species and diffusion of the reaction substrates / products, ii) the conditions in which copper-gold alloy-like structure was formed, iii) the effect of gold and copper on the reaction pathway, iv) the changes on the catalyst surface caused by the oxidation of propene and v) the role of acidity on the reaction selectivity. One of the most important findings from this work was the evaluation of the conditions in which copper and gold species were introduced to be in vicinity which led to the effective oxidation of propene to acrolein. It was found that such a vicinity can be achieved by gold-copper alloy formation during hydrogen reduction and next separation of the two components upon exposure to the reaction conditions. The reaction pathway was also considered and discussed.

The aim of this study was to prepare and characterize the bifunctional catalysts containing copper (redox source) and boron (acidity source) loaded on SBA-15 for catalytic methanol oxidation. Copper and boron species were loaded by sequential impregnation or co-impregnation, and three series of materials were prepared: series Cu-xB with copper loaded prior to boron, series xB-Cu with boron loaded prior to copper, and series xBCu with copper and boron co-impregnated (x designated B/Cu molar ratio; x = 0.5, 1 and 3). The materials were characterized by XRD, N2 physisorption, XPS, UV–vis spectroscopy, and combined H2-TPR/N2O oxidation analysis and were also investigated by test reactions of 2-propanol decomposition and pyridine adsorption combining with FTIR. The results showed that the strength of the interaction between copper and boron was depended on the sequence of incorporation, and that the materials contained only Lewis acid sites with acidity strength weakened with increasing boron amount. The roles of preparation procedure, content of boron, strength of interaction between boron and copper species, strength and number of Lewis acid sites were considered in the context of activity and selectivity in methanol oxidation. The series xB-Cu catalysts showed higher activity for the oxidation of methanol than other two series, and for xB-Cu catalysts the addition of boron lowered the reducibility of copper oxides. The best catalyst was found to be 1B-Cu, which exhibited relatively high activity, high selectivity to methyl formate and formaldehyde, and high stability.

A series of bimetallic silver-platinum catalysts based on pure-silica mesostructured cellular foam (MCF) with various Ag/Pt atomic ratios were prepared, tested in methanol oxidation and propene oxidation and characterized by UV–vis spectroscopy, X-Ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS) and Transmission Electron Microscopy (TEM). Bimetallic catalysts were not more active than monometallic ones in propene oxidation but their selectivity to acrolein was significantly higher, especially over 4AgPt/M activated in inert gas. This catalyst showed also high activity and selectivity to methyl formate in methanol oxidation. Upon activation of the catalysts in different environments and oxidation reactions, the reduction of silver oxide and segregation of bimetallic nanoparticles took place. This effect was the highest upon activation in hydrogen flow and was responsible for exposition of metallic platinum leading to high conversion of substrates (methanol or propene) and their total oxidation. Segregation of bimetallic species and increasing dispersion after activation and exposition of the activated samples to the reagents (propene, methanol, oxygen) were consequences of the mobility of silver species and their susceptibility to change the oxidation state.

The aim of this work was to evaluate the catalytic activity of new Au-Fenton-like catalyst in degradation of methylene blue at ambient conditions. For this purpose gold nanoparticles were deposited on commercial ZnO and the material prepared in this way was characterized with N2-adsorption and desorption, XRD, XPS and TEM. The catalyst ability to formation of reactive oxygen species (ROS) upon treatment with H2O2 was investigated with the use of o-phenylenediamine (OPD) and nitrotetrazolium blue chloride (NBT) reactants. Degradation of methylene blue was tracked by UV–vis and ESI-MS. The efficiency of dye mineralization was determined by the analysis of total organic carbon (TOC). On the basis of results obtained the role of different types of ROS in dye degradation was demonstrated. It was also demonstrated that the activity of Au/ZnO Fenton-like catalyst can be enhanced by visible light irradiation.

Layered zeolites of MWW family, MCM-22 and pillared MCM-36, were used as supports for base modifiers: cesium species (introduced via cation exchange or impregnation) and 3-aminopropyl trimethoxysilane (AP). The obtained materials were characterized by different methods (ICP-OES, N2 adsorption, XRD, XPS, TG/DTA, FTIR combined with pyridine adsorption, 2-propanol decomposition) for evaluation of chemical, structural and surface properties. All materials obtained were subjected to the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and ethyl acetoacetate. The effect of the zeolite structure, the stability of the catalysts as well as acid-base properties of zeolites on the activity in Knoevenagel condensation were considered. Of particular interest was the role of Bronsted acid sites (BAS). The nature of basic sites and BAS played different roles depending on the methylene compound used in the Knoevenagel condensation. AP-modified zeolites were the most active in the condensation between benzaldehyde and ethyl cyanoacetate, in which, in the first step of the reaction AP abstracted hydrogen from methylene carbon in ethyl cyanoacetate. A different reaction pathway was postulated for the condensation with ethyl acetoacetate on the basis of the highest activity of unmodified zeolites and the relationship between benzaldehyde conversion and the number of BAS. For this reaction protonation of benzaldehyde was postulated as the initial step of the reaction.

Niobium and cerium dopants of mesoporous cellular foams, MCF, have been recently considered as promoters enhancing the basicity of amino-organosilanes anchored to the supports. Thus, the knowledge of acid-basic properties of niobium and cerium containing MCFs is important. Therefore, in this work monometallic (Ce and Nb) and bimetallic (Ce + Nb) materials based on MCF were investigated by means of NO and pyridine adsorption combined with infrared (FTIR) and electron spin resonance (ESR) spectroscopies as well as test reactions. The properties of bimetallic materials strongly depended on the method of impregnation (one-pot vs. step-by-step procedure). If niobium was included in step-by-step method (first niobium and next cerium sources – Ce/Nb/MCF) the Nb species were incorporated to silica skeleton and ceria surrounded some of the framework niobium species (NbO−) enhancing the acidic strength of tetra-coordinated niobium cations playing the role of Lewis acid sites (LAS). One-pot modification (simultaneous impregnation with Nb and Ce sources – CeNb/MCF) resulted in the formation of niobium and cerium oxides showing synergistic interaction. In this system ceria was more defected than in Ce/Nb/MCF sample and acidic strength of niobium species (LAS) was lower.

The Knoevenagel condensation with chlorine substituted benzaldehyde is difficult because of deactivation of aldehyde group. In this work we have shown that the activity of mesoporous cellular foams (MCF and Nb/MCF), modified with 3-aminopropyl-trimethoxysilane (AP) as a source of basicity, can be enhanced for this reaction by the anchoring of gold species. Gold species were loaded on amine modified materials towards Au/AP-MCF and Au/AP-Nb/MCF. Moreover, copper was used as a dopant for the latter sample giving rise to AuCu/AP/MCF. All these materials were characterized in details by different complementary techniques (N2 adsorption isotherms, TEM, UV–vis, TG/DTA, XPS, DFT calculations) which allowed the evaluation of states of all components of the catalysts. The interaction between niobium species and AP was evidenced to increase the stability of the basic modifier. This interaction was weakened by the introduction of gold and copper. The presence of both, negatively charged gold nanoparticles (NPs) and gold cations was crucial for the activation of 2,4-dichlorobenzaldehyde via the interaction with chlorine substituent atoms and aldehyde oxygen atoms as well as breaking of the “pseudo hydrogen bond” between aldehyde hydrogen atom and chlorine substituent, which destabilized the structure making it more active. Gold dopants did not influence significantly the condensation of ethyl cyanoacetate with benzaldehyde.

TaMCF silicas modified with alkaline metals can be considered a novel family of highly efficient bifunctional catalysts involved in the synthesis of chromene derivatives, from salicylaldehyde 2 and acetonitrile compounds, under mild conditions, showing enhanced catalytic performance than their NbMCF analogues. The observed reactivity was mainly attributed to the higher basicity of the Me/TaMCF but also the texture of the samples. The Me/TaMCF silicas showed higher Bronsted basicity than the Nb ones as indicated by the stronger interaction between alkali metals and Ta in the UV–vis and the test reaction experiments. On the other hand, the basicity of Me/TaMCF together the reactivity degree and steric hindrance of the starting acetonitriles are key factors influencing the reaction selectivity. In conclusion, the basicity of the samples plays an important role initiating the reaction by activation of nucleophile but also a compromise between alkaline cation size and basicity is required.

New heterogeneous catalysts were obtained by modification of MWW zeolites (MCM-22 and MCM-56) by swelling and pillaring with niobiosilicate, achieved by two different methods. The main differences between these methods were time and temperature at which the modification was carried out, the concentration of a base used during the modification, and the water content in the catalysts used for further modification. The XRD analysis proved that both methods used gave MCM-36 structure, in all cases pillaring led to an increase in surface area, but some differences in final materials were noted, depending on the pillaring procedure. Both NbMCM-36 zeolites exhibited different content of micropores (lower in the zeolites synthesized from MCM-22), different loading with niobium species (higher in the material prepared from MCM-56) and similar acidity strength. Both niobium containing zeolites were active catalysts in liquid phase cyclohexene oxidation with H2O2 and were successfully used in the second run. Niobium played a role of H2O2 activator. Texture parameters and content of niobium was crucial for the effective discoloration of methylene blue with the use of hydrogen peroxide.

N-bromobenzyl substituted (E)-4′-hydroxy-4-stilbazolium bromide (NBSB), a representative of azastilbene compounds which reveals strong solvatochromism, was used as a probe molecule for testing basicity of nitrogen organic compounds grafted on mesoporous cellular foam silica (MCF). Easy deprotonation of this compound in contact with basic species was the reason for its use for probing the basicity of AP/MCF (AP - (3aminopropyl)trimethoxysilane), Im/MCF (Im - N-trimethoxysililpropylimidazole) and Az/MCF (Az - (3-azidopropyl)(triethoxy)silane). NBSB and its deprotonated form were analyzed by UV–vis spectroscopy measurements in solutions and UV–vis in solid materials. Ab-initio calculation allowed distinction between the preference of NBSB for interactions with SiOH on the support surface and with nitrogen species of the modifier. The NBSB protonation - deprotonation equilibrium dependence on pH was indicated. The role of solvent was considered. In water indirect probing of basicity by NBSB was observed via abstraction of proton from solvent by the modifier and deprotonation of NBSB due to the increased pH of the solution. In acetonitrile direct basicity probing took place in which NBSB was adsorbed in MCF pores. AP/MCF and Im/MCF caused deprotonation of NBSB, as monitored by UV–vis reflectance spectra. This effect was stronger for AP/MCF, which showed higher basicity. Az/MCF could not deprotonate NBSB in either water or acetonitrile.

The study was aimed at comparison of the stability and effectiveness of anchoring of the amine and sulfonic groups formed on mesoporous silica by the click reaction. The impact of silica dopant (niobium) and the structure of mesoporous silica (hexagonally ordered SBA-15 vs cellular foam MCF) on the properties and behavior of these surface groups was characterized in details. The modifiers stability was found to have a significant effect on the catalytic reactions in liquid phase. In order to increase the catalysts stability, the mesoporous silica and niobiosilicate were used as supports for ((3-azidopropyl)(triethoxy)silane) – AZPTES followed by the condensation with propargylamine or propargylsulfone by the click reaction performed in the presence of different copper salts used as catalysts of the process. The number of copper ions left in the material after the click reaction was also estimated.

International audience; Zinc oxide species grafted on mesostructured cellular foam (MCF) silica are investigated using a combination of experimental and theoretical techniques. MCF is modelled using a realistic amorphous silica surface model surface slab. The most energetically favorable complexes grafted on the silica surface were identified and characterized at the molecular level. The Zn metal center was found in tetrahedral coordination. Moreover, the Si-O-Zn-OH species is found to be stabilized in a 5 fold coordinated silicon with an unusual trigonal bipyramidal geometry. A mechanism for the grafting process of the metal species on the support is proposed.

SBA-15 mesoporous materials were modified with calcium species (up to 40 wt% of Ca) using calcium acetate and calcium nitrate salts. Niobium species were also incorporated into the SBA-15 support. The structure and surface properties of final materials were examined using XRD, N 2 adsorption/desorption, XRF, UV–vis, FTIR as well as cyclization and dehydration of 2,5-hexanedione. The impact of niobium species on stability of mesoporous solids was investigated. It was found that niobium stabilizes the structure of the support upon its modification with calcium salts. The procedure applied in this work allowed obtaining basic catalysts with high surface area of Ca content up to 40 wt%.

The aim of this study was to use gold catalysts supported on niobium(V) oxide and mixed niobium-zinc oxide in methanol oxidation and to characterize step by step changes in the surface of catalysts that were caused by the activation of the catalyst and methanol oxidation. The purpose was to identify the species important for the activity and selectivity of the reaction. The following surface species were identified by XPS in as prepared catalysts: (i) highly nucleophilic oxygen with the excessive negative charge; (ii) lattice oxygen O 2− in the metal oxide; (iii) oxygen in surface hydroxyls; (iv) negatively charged gold NPs (Au 0 ) δ− ; and (v) metal cations (niobium, zinc and gold). Activation of catalysts resulted in dehydroxylation accompanied by the formation of highly nucleophilic oxygen and metallic gold showing low activity in selective methanol oxidation. The interaction of the reaction products changed surface species towards basic hydroxyls and next to (Au 0 ) δ− inducing the activity jump and total oxidation of methanol.

This review article is devoted to the materials containing niobium and modified by the addition of different metals or thio- and amino-organosilanes towards the creation of new surface properties and enhancement of catalytic activity. The intention is to show and discuss the role of niobium supported on molecular sieves in the enhancement of the redox properties of transition metals (copper, silver, gold, platinum) and acidic or basic properties of the catalysts as well as to consider redox properties of pure and modified bulk niobium(V) oxide. This paper covers the contribution to the knowledge of this area brought over the last 15 years by our research team.

Silica mesoporous cellular foam (MCF) was modified with niobium or both niobium-zinc species and then gold, copper or both gold-copper were loaded on such prepared supports to obtain multifunctional catalysts active in methanol oxidation. The main focus was on the study of the interactions between elements introduced to the catalysts and their role in the surface and catalytic properties in order to new understanding of catalysts addressed to oxidation of alcohols. The catalysts were characterized by ICP-OES, low temperature adsorption/desorption of nitrogen, XRD, XPS, SEM, STEM, SEM combined with EDX, UV–vis DRS, FTIR after adsorption of pyridine. It was proved that tetra-coordinated niobium species in Au-Nb/MCF and AuCu-Nb/MCF strongly interacted with metallic gold. The interaction was lowered by the considerable interaction between zinc and niobium species in Au-NbZn/MCF and AuCu-NbZn/MCF. The synergistic effect between gold and copper caused a decrease in the gold interaction with the elements introduced into the supports. The interactions between components of the catalysts were responsible for electrons mobility important in oxidation of methanol. The role of each ingredient, i.e. metallic gold – active phase, copper, niobium and zinc species – structural and electronic promoters and additional active phase (Lewis acid sites) was determined. The highest rate of methanol oxidation was achieved on AuCu-NbZn/MCF, i.e. the sample containing four metal components. The product distribution was explained on the basis of acidity strength that determines adsorption/desorption of methanol and byproducts on the surface active centers.

SBA-15, NbSBA-15, Ca/SBA-15 and Ca/NbSBA-15 were tested as supports for gold in order to obtain effective catalysts for environmentally friendly base-free aerobic selective oxidation of glucose to gluconic acid. Detailed characterization of all catalysts and analyses of their activity allowed to determine the most important features conducive to high efficiency of gold catalysts in this reaction. These features include relatively large/medium sized gold particles endowed with negative charge and the support composition which ensures that negatively charged gold species are exclusively present in a fresh catalyst. Metal-support and reagent-support interactions are attributed to chemical composition of the supports. The most active catalyst was Au/SBA-15 in whose negatively charged gold particles were active in both glucose chemisorption and oxygen adsorption in the form of superoxo species. According to our knowledge the role of negatively charged gold particles in glucose oxidation is considered for the first time. Au/SBA-15 catalyst has been found promising because of its very high activity in glucose oxidation, easy preparation procedure and relatively high stability. Calcium dopant in Au/Ca/SBA-15 enhanced dispersion of gold, stabilized the catalyst but only in four initial reaction cycles and decreased the activity by lowering of zeta potential.

Mesoporous silicas and niobiosilicates of SBA-15 and MCF types were modified by anchoring of imidazole, characterized (XRD, N2 adsorption/desorption, XPS, TEM, UV–vis, FTIR, TG/DTA, TG/MS) and tested as catalysts in the Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate, the reaction involving the basic active centres of catalysts. Moreover, the behaviour of functionalization agent used before imidazole loading, (3-chloropropyl)trimethoxysilane (ClPTMS), was studied in detail. The use of mesoporous materials of different structures as supports allowed the discussion of the structure effect on imidazole loading and stability. Imidazole was preferentially located in the windows of MCF structure. The novelty in the formation of new catalysts was the use of niobium containing mesoporous silicas as the supports for imidazole. Niobium species in NbSBA-15 and NbMCF interacted weakly with imidazole anchored and much stronger with ClPTMS enhancing the effectivity of imidazole anchoring. In this paper, for the first time, the reaction pathway of transformation of both modifiers, ClPTMS and imidazole, upon thermal treatments was established and documented. In this way, the influence of different bonding of imidazole to mesoporous silica on the activity in the Knoevenagel reaction was explained. For the higher activation temperature, the lower conversion of benzaldehyde was observed. The catalytic activity of imidazole species was enhanced by the niobium presence in the support, working as Lewis acid site and taking part in the reaction (the carbonyl of the aldehyde is activated by acidic sites) and by the more open structure of MCF supports than that of SBA-15 one.

We report the synthesis, characterization and activity of new series of catalysts based on Niobium Mesoporous Cellular Foams (NbMCF), modified with alkaline metal elements. These materials exhibit very different acid-base properties attributed to the Nb source for the preparation of the catalysts and the presence and loading of different alkaline metals. The Me/NbMCF materials (where Me are alkaline metals) were tested in the reaction of 2-hydroxybenzaldehyde and ethyl cyanoacetate, under solvent-free conditions, at room temperature, leading to mixtures of the corresponding chromenes 4 and 5, as mixtures of diastereomers erythro/threo, in a 2:1 ratio, respectively, with good to excellent yields. Our experimental results indicate that the metal loading on the catalysts and the acid-base character, and the texture parameters are probably determining factors in the reactivity and the observed diastereoselectivity. The computational study suggests that the presence of alkaline oxides on Me/NbMCF catalyst, exhibiting strong basicity, activates the formation of the nucleophile species, the corresponding enolate, and initiates the reaction. However, the cation size has a deep impact on the stability of the reactant complex so that the effective aldolization could be obstructed by the presence of the bulkier centers.

CeO2, ZrO2 and mixed CeZrOx (Ce:Zr = 1:1 assumed) mesoporous oxides were synthesized and used as supports for gold (nominal 1.5 wt%) and copper (nominal 2 wt%). The materials obtained were characterized by UV–vis, XPS and TEM techniques, which allowed monitoring of the oxidation state of metals and surface properties of the catalysts, in particular the concentration of the components on the surface of the solid and in the bulk of the material. The metal-support and metal–metal (in bimetallic Cu-Au samples) interactions were considered. The aim of this work was to investigate the changes in chemical composition of catalyst surfaces and the oxidation states of metals upon the activation of the samples at different temperatures (423 and 573 K) in the argon flow and evaluation of the influence of these changes on the catalytic activity and selectivity in the low temperature oxidation of methanol. It was evidenced that the electronic state of gold and the mobility of metals towards and oxygen from the support play an important role in the low temperature total combustion of methanol. The activation temperature strongly affects the mobility of surface oxygen and the oxidation states of the cationic components playing the role of Lewis acid sites (it causes an increase in Cu+ and Ce3+ species concentration and a decrease in that of cationic gold on the surface after thermal treatment), and therefore strongly affects the activity and selectivity in the oxidation of methanol. The catalysts effective in low temperature total combustion of methanol are proposed.

A series of bifunctional heterogeneous catalysts based on SBA-15 supports modified with Zr, Nb and Mo species functionalized by aminopropyl siliceous species has been used in the Knoevenagel condensation. The results indicated that the acid–base synergetic effects of the centres present on these catalysts seem to have significant effect on the Knoevenagel condensation of benzaldehyde with active methylene compounds. Basic sites and Lewis acid sites play different roles depending on the methylene compound used in the Knoevenagel condensation. Depending on the chemical composition of the catalysts, the reaction can proceed on basic sites exclusively or on the pairs of acidic-basic centres. The nature of metal species strongly influences the activity in the Knoevenagel condensations but does not affect the selectivity.

The aim of this work was to evaluate the effect of pillaring of MCM-22 zeolite on Pt and Au dispersion and catalytic activity in CO and methanol oxidation as well as to analyze the similarities and differences in the surface and catalytic properties of Au and Pt loaded on pillared MCM-22-pil. The role of pillaring in the functionalization by APTMS (3-aminopropyl-trimethoxysilane) before metal loading was also considered. The difference in the effect of platinum and gold dispersion on the rate of CO oxidation confirmed reports in the literature. The stability of Pt-containing zeolites in CO oxidation for the second run of the reaction is pointed out. An increase in activity of gold catalysts in the second cycle of the reaction was found and is discussed. The difference found in the methanol conversion and selectivity in alcohol oxidation between gold-containing MCM-22 and MCM-22-pil is discussed.

MCF, NbMCF and TaMCF Mesostructured Cellular Foams were used as supports for platinum and silver (1 wt%). Metallic and bimetallic catalysts were prepared by grafting of metal species on APTMS (3-aminopropyltrimethoxysilane) and MPTMS (2-mercaptopropyltrimethoxysilane) functionalized supports. Characterizations by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) spectroscopy, and in situ Fourier Transform Infrared (FTIR) spectroscopy allowed to monitor the oxidation state of metals and surface properties of the catalysts, in particular the formation of bimetallic phases and the strong metal–support interactions. It was evidenced that the functionalization agent (APTMS or MPTMS) influenced the metals dispersion, the type of bimetallic species and Nb/Ta interaction with Pt/Ag. Strong Nb–Ag interaction led to the reduction of niobium in the support and oxidation of silver. MPTMS interacted at first with Pt to form Pt–Ag ensembles highly active in CH 3 OH oxidation. The effect of Pt particle size and platinum–silver interaction on methanol oxidation was also considered. The nature of the functionalization agent strongly influenced the species formed on the surface during reaction with methanol and determined the catalytic activity and selectivity.

The role of water present in the mesopores of SBA-15 on the level of (3-mercaptopropyl)trimethoxysilane (MPTMS) and ((3-aminopropyl)trimethoxysilane (APTMS) for comparison) loading and their stability were studied by experimental and theoretical approaches. N2 ads./des., XRD, XPS, FTIR, thermogravimetry and elemental analyses were used for materials characterization. The results obtained from the periodic DFT calculations and the ab initio molecular dynamics (AIMD) simulations were analyzed to study various possible structures of anchored MPTMS on the surface of SBA-15. Experimental results were very well consistent with theoretical calculations and indicated that the higher the amount of water in SBA-15 the higher the level of modifier loading was obtained. Theoretical calculations allowed the explanation of such feature. The effect of water and modifier concentration in SBA-15 on the oligomerization of MPTMS was considered. The catalytic activity was analyzed in the context of the anchored modifier amount and forms. The H2S release and C C bond formation in the modifier moiety after thermal treatment of the sample in vacuum was analyzed. The effect of water on the efficiency of MPTMS loading on differently hydrated SBA-15 as well as on its forms and properties is presented for the first time, according to our knowledge.

The abilities of niobium and manganese to enhance oxidation of thiol groups in (3-mercaptopropyl)trimethoxysilane (MPTMS) used for functionalization of SBA-15 and MCF materials, by hydrogen peroxide in order to form catalysts with acidic properties were evaluated. Materials obtained were characterized by: N 2 adsorption, XRD, XRF, elemental and thermal analyses and titration of acid sites. The highest concentration of acidic sites was found for SBA-15 structure modified with niobium. The catalytic activities of materials obtained were examined in esterification of acetic acid with ethanol and 2-propanol. Both niobium containing samples (MP-NbSBA-15 and MP-NbMCF) showed high yields of ethyl and 2-propyl acetate. The amount of 2-propyl acetate formed was found to linearly depend on the number of acid sites on the catalyst surface. The reuse tests proved that the drop in the catalyst activity in consecutive catalytic cycles is not too high, which suggests possible application of the materials obtained after further optimization.

Commercial silica (Ultrasil – BET surface area 158 m2/g) was modified with platinum and/or silver. Before metal loading, the silica was functionalized with one of the following organosilanes, 3-aminopropyltrimethoxysilane (APTMS) and 2-mercaptopropyltrimethoxysilane (MPTMS) or both of them. It was proved that the nature of organosilane (MPTMS or APTMS) used for functionalization of silica before silver and platinum loading, played an important role in the anchoring of Pt and Ag species and affected the kinds of bimetallic particles formed. The creation of alloy-like bimetallic structure depends on a combination of two parameters, the nature of organosilane and the method of modification by platinum and silver. If the one-pot method of modification was used, the functionalization of silica by MPTMS favoured alloy formation (PtAg/Si-M and PtAg/Si-AM samples). APTMS functionalization promoted alloy formation if the step-by-step modification was applied, independently of the sequence of metals loading. Core–shell structure was formed only if MPTMS functionalization of silica was used and silver species were loaded first (1Ag2Pt/Si-M sample). Bimetallic particles were not formed in two samples, PtAg/Si-A and 1Pt2Ag/Si-M. The presented results have proved that selectivity of bimetallic catalysts in methanol oxidation depends on metals loading and dispersion, whereas their activity is influenced by the interaction between platinum and silver in bimetallic particles. The highest selectivity to methyl formate (84%) for 100% conversion of methanol was reached over PtAg/Si-M at 373 K.

SBA-15 with ceria and/or zirconia modified with gold and copper are characterized by spectroscopic methods and their performance for the carbon monoxide oxidation is estimated. Surface properties of the materials and catalysts containing Cu and Au are highlighted and discussed considering the interaction between Ce, Zr, Au and Cu with the emphasis on redox properties. Au–Cu interaction prevents the agglomeration of gold particles at higher temperature. It is shown that gold particle sizes in bimetallic (Au + Cu) samples are smaller than in monometalic (Au) ones. It results in higher activity in CO oxidation. Cu–Zr interaction determines the strength of CO chemisorption on copper species and its further oxidation. The Cu–Zr interaction results also in easy reduction and reoxidation of copper species in the reaction runs. Interaction of copper species with gold and zirconium leads to modification of chemisorption of CO which interacts with active, mobile oxygen transferred from the surface through gold nanoparticles. The right composition of SBA-15 modifiers (cerium and zirconium oxides 1:2) allowed to increase the activity of gold–copper catalysts in CO oxidation.

Catalytic behaviour of supported nanometal catalysts for alcohols selective oxidation depends on the nature of the support and its surface. To identify the main feature that could explain these effects, supported mono- (Au) and bimetallic (AuAg) catalysts were prepared by using pure MgO, ZnO and Nb2O5, representative of three different types of oxides (basic, amphoteric and acidic, respectively), to get homogeneous metal-support interaction for each catalyst. The catalysts were characterized by XRD, N2 physisorption, TEM, UV–vis, XPS and 2-propanol decomposition as test reaction. It was found that the catalytic activity is influenced by the electron mobility between the gold nanoparticles and the support, which in turns depends on the intermediate electronegativity of the support. Selectivity in n-octanol oxidation was determined by redox properties of the gold species, the acid-base properties of the supports and the catalyst pretreatment. Silver addition modified the acid-base properties of the catalytic system, thus influencing the selectivity in n-octanol oxidation. Pretreatment of the catalyst (drying in air or thermal treatment in hydrogen flow) had a significant impact on its activity and selectivity.

Hydrogen forms of layered MCM-22 and delaminated MCM-56 zeolites were modified with molybdenum species. The structure/texture and surface properties as well as catalytic activity in methanol transformation and dibutyl sulphide oxidation were compared for the two types of modified zeolites. The difference in the distribution of hydroxyls in HMCM-22 and HMCM-56 (more Bronsted acid sites (BAS) on HMCM-22, their high strength on HMCM-22, and domination of external silanols in HMCM-56) determines the location and properties of MoO 3 . Mo species interact with BAS on Mo/HMCM-22, which results in good dispersion of MoO 3 and harder reducibility of molybdenum. Preferential interaction of Mo species with silanols on the external surface of HMCM-56 leads to larger crystallites of MoO 3 which are easier to reduce. The strength of BAS is lower in HMCM-56 than in HMCM-22 and it is reduced in HMCM-22 after modification with Mo species. The lower strength of BAS in HMCM-56 results in a higher selectivity to 2-butene in the transformation of methanol, reaching 98.5% for Mo/HMCM-56. Mo species play a crucial role in the oxidation of sulphide to sulphoxide by H 2 O 2 . MoO 3 is less stable in Mo/HMCM-56 because of the weaker interaction with the external zeolite surface. It is leached to the solution during oxidation of dibutyl sulphide. Therefore, Mo/HMCM-22, where Mo species are stronger bound to the surface, is more effective catalyst for this reaction.

Transition metals of group IV (Zr), group V (Nb), and group VI (Mo) were introduced into SBA-15 materials during the synthesis towards the production of metallosilicates, MSBA-15, to be used as supports for 3-aminopropyl-trimethoxysilane (APTMS), and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (3APTMS). The materials obtained were characterized by N 2 adsorption/desorption, XRD, TEM, ICP, XPS, UV–Vis, FT-IR and pyridine adsorption. The results indicated that the metals were loaded in the cationic state: Zr 4+ , Nb 5+ and Mo 6+ and preferentially located on the SBA-15 surface. The highest efficiency of metal loading in SBA-15 under the conditions used in this work was reached for molybdenum, whereas the highest metal content on the surface was observed for ZrS. The number of Lewis acid sites (LAS) changed in the following order: ZrS ≫ NbS > MoS, whereas their strength as follows: ZrS > NbS ⩾ MoS(HP). Zirconium containing material exhibited additionally BrOnsted acidity. The efficiency of propyl-amine incorporation changed according to the electron state of metals: Zr

Mesostructured cellular foams (MCF) doped with Nb or Zr were used as matrices for preparation of gold catalysts for oxidation of methanol. The focus was on the characterisation of Au–NbMCF and Au–ZrMCF materials as well as the effect of Au–Nb or Au–Zr interactions and the gold particle sizes on the activity of MCF catalysts in the selective MeOH oxidation towards formaldehyde. The samples prepared were characterised by XRD, N2 adsorption/desorption, TEM, UV–Vis, XPS, H2-TPR, FT-IR combined with the adsorption of pyridine and test reaction. The results allowed defining the location and coordination of Nb and Zr in the structure of MCF, the state of gold on the surface as well as the acid/base properties of the catalysts obtained. The results showed that the bifunctionalised gold catalysts containing Nb and Zr are highly active in selective methanol oxidation in the temperature range 523–623 K. The presence of gold significantly enhanced the activity, whereas the Nb and Zr additives influenced the selectivity of the catalysts. Au–NbMCF and Au–ZrMCF appeared to be useful for the production of formaldehyde by methanol oxidation.

Au- and CeO 2 -containing catalysts, supported on SBA-15 mesoporous molecular sieves and loaded with additives such as Cu and Zr species, were obtained and characterised. Cerium oxides are preferentially located in the bulk of SBA-15, whereas Zr species on its surface. Gold and copper loaded on supports strongly interact resulting in the electron transfer from Cu + to metallic gold, thus enhancing redox properties. Moreover, cerium species interact with gold, increasing redox properties of the system. The presence of copper increases the gold dispersion. Ce- and Zr-containing supports contain Lewis acid sites (LAS). The number of LAS is increased by the modification with copper species, whereas gold loading diminishes the LAS content. The presence of Zr species is responsible for Bronsted acidity and directs the oxidation of methanol to dimethyl ether. Copper enhances the selectivity to methyl formate. Gold and cerium are responsible for total oxidation of methanol, which is enhanced by modification with copper. The most attractive catalyst for low temperature total oxidation of methanol is bimetallic AuCu/CeSBA-15.

The influence of hydrogen peroxide on the efficiency of Rhodamine B (RhB) photooxidation over Nb2O5, which exhibits unique ability to generate strongly oxidative species both upon irradiation with UV light and upon treatment with hydrogen peroxide, was investigated. According to the results, niobia displays low activity in RhB discoloration by photocatalytic and Fenton-like processes, but the efficiency of the reaction is greatly improved when both advanced oxidation processes are combined. The tests with the use of various reactive oxygen species scavengers revealed that the crucial species responsible for the improved efficiency of RhB discoloration in the hybrid process were superoxide radical anions (O2•−) and singlet oxygen (1O2). It was documented that the former species exhibited low activity in RhB discoloration, but they were the precursors of the latter species, which played the key role in the dye discoloration.

Phosphorus (P) was introduced into MCF and NbMCF materials during one-pot synthesis and by post-synthesis modification. The materials obtained were used as supports for grafting of (3-mercaptopropyl)trimethoxysilane (MP) oxidized by H 2 O 2 to transformation of SH towards sulphonic groups. The focus in this work is on the deep insight into the textural parameters of the materials, estimation of the efficiency of P and Nb incorporation into MCFs, surface acidic properties and activity and selectivity in acetic acid esterification with glycerol. Phosphorus is much easier included into the structure of MCF when the source of niobium is present in the synthesis gel. However, much higher amount of phosphorus is loaded by the impregnation procedure. Niobium has an influence on thiol species oxidation (in MP) leading to obtain a higher amount of acidic centers. The introduction of P species creates the additional Bronsted acid sites (BAS). The best performance in catalytic esterification of acetic acid with glycerol shows the material prepared in one-pot synthesis with the use of all components (Nb, P and MP).

The aim of this work was to compare the properties of niobium (Si/Nb = 118) and tantalum (Si/Ta = 121) containing mesostructured cellular foams (MCF) modified with (3-mercaptopropyl) trimethoxysilane (MPTMS) in one-pot synthesis and the application of materials obtained in acetic acid esterification with glycerol. TaMCF materials were prepared for the first time. Catalysts were characterized by different techniques: N 2 adsorption, XRF, elemental and thermal analyses, FTIR + pyridine adsorption and titration of acid sites. New catalysts have showed an excellent catalytic activity in the acetic acid esterification with glycerol to yield triacetylglycerol, also known as triacetin (a valuable additive for biodiesel composition). The influence of modifiers on the number and strength of acidic centres in the materials obtained was found and discussed in details in the paper. The strength of Bronsted acid centres (BAS) was estimated by the interaction of organosilane with transition metal via the use of methoxy groups from MPTMS. The highest concentration of acidic sites determined by NaOH titration was obtained on tantalum modified MCF, whereas the highest strength of BAS was observed on MP-NbMCF sample. The catalytic behaviour of MPTMS and Nb modified MCF samples was comparable to that observed for Amberlyst 15 and better than that of Nafion SAC 13. The materials obtained could be reused and showed stable catalytic features in subsequent cycles. The addition of tantalum allows obtaining a new catalyst with high efficiency of thiol species oxidation (higher than reported before for other catalysts). MPTMS modified TaMCF material appeared to be attractive for further study in different reactions requiring high concentration of acidic centres.

Amorphous and crystalline niobium(V) and tantalum(V) oxides were treated with hydrogen peroxide and studied by XRD, UV–vis, FTIR and ESR techniques to identify changes on their surface upon interaction with hydrogen peroxide. Differences between amorphous and crystalline materials in the interaction with H2O2 depending on the hydroxylation of the surface and the nature of OH groups were evident. The type of radical species formed on hydroxylated amorphous materials treated with H2O2 depended on the nature of metal oxide. It was proved that peroxo radical species formed in the interaction of H2O2 with amorphous Nb2O5 were the active intermediates in the oxidation of glycerol to glycolic acid with hydrogen peroxide. The radicals formed on amorphous Ta2O5 surface treated with hydrogen peroxide were poorly active in the oxidation of glycerol. Detailed study of the above mentioned radicals is in progress and will be a subject of a separate paper.

Graphical abstract: Display Omitted Highlights: ► Interaction of gold with K leads to the change of electronic state and redox properties of gold. ► The amount of potassium incorporated into Au-zeolites determines the size of gold particles. ► K(0.2 wt.%)/Au-Beta exhibits the best performance in decomposition of N{sub 2}O and removal of Bu{sub 2}S. -- Abstract: Beta zeolite was applied as support for gold introduced by gold-precipitation method and potassium added by impregnation or adsorption. The effect of zeolite composition and the amount of potassium introduced on the surface properties of the final materials was considered. Moreover, the interaction of gold and potassium species was found to be related to the adsorptive and catalytic behaviour of zeolites in NO reduction with propene and deodorization. K/Au-Beta(Impregnated) exhibits the best performance in the above mentioned processes because of the small gold particles (between 2 and 5 nm) and interaction of gold with potassium species leading to the change of electronic properties of the surface (the appearance of cationic gold species). Potassium added as a promoter improves the catalytic properties of Au-zeolite in N{sub 2}O decomposition and also in deodorization (increase of the ability to dibutyl sulphide oxidation). The catalysts prepared were characterizedmore » by XRD, XPS, UV–vis, TEM, pyridine adsorption combined with FTIR and test reaction (2-propanol transformation).« less

Amorphous NbMCM-41 and crystalline NbY zeolite were characterized by the adsorption of NO (or oxygen admission followed by NO adsorption) combined with FTIR measurements. XRD, XPS and UV–vis results proved that in both types of materials Nb was present as +5 cation in a tetrahedral coordination involved in Nb–O–Si bonds and no extra framework niobium species were formed. Despite these common features, a substantial difference between the niobium species in these two types of materials was indicated by NO adsorption and FTIR study. In NbMCM-41 activated at 673 K, unsaturated Nb δ+ formed Nb–NO complexes whereas NbO δ− species were responsible for nitrate formation. In NbY zeolite the niobium cations in the framework were saturated and did not form Nb–NO complexes. The interaction of NO with the residual water was documented by the formation of N 2 O after NO adsorption on NbY. The increase in basicity of Y zeolite after Nb introduction was proved by the formation of nitrite species resulting from electron transfer from the zeolite to NO 2 .

Mesoporous silica and niobiosilicate materials of SBA-15 and MCF types were prepared in the presence of MPTMS, i.e. (3-mercaptopropyl)trimethoxysilane and hydrogen peroxide. The samples obtained were characterised by different techniques (N2 adsorption/desorption, XRD, elemental and thermal analyses) and applied as catalysts in glycerol esterification with acetic acid. The role of niobium species on the formation of sulphonic species and stability of organosilane modifier was explored. The most important finding is that the addition of niobium to the synthesis gel improves the efficiency of –SH oxidation by hydrogen peroxide towards sulphonic species. This behaviour is not dependent on the type of structure of mesoporous materials (SBA-15 or MCF). However, the kind of mesoporous solid influences the efficiency of Nb incorporation and on the esterification process. MCF matrix improves the catalytic performance of the MPTMS modified catalyst.

Purely siliceous and niobium-containing mesoporous molecular foams (MCFs) were synthesized by modifying a standard synthesis route. This was accomplished by decreasing considerably the content of chloride ions in the gel. The samples prepared under such conditions contained the MCF and SBA-15 phases. Mesostructured cellular foams were modified with (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)trimethoxysilane (APTMS) via the direct synthesis, with increased efficiency of formation of the spherical MCF phases. All the materials obtained were characterized by XRD, sorption of nitrogen, FT-IR, UV–Vis, thermogravimetric analysis, 29Si MAS NMR, 13C CP/MAS NMR, and electron microscopy. We demonstrated that organosilanes added at the end of the synthesis procedure play a double role; as a source of the anchored catalytic active species (propylamines and propylsulfonic chains) and a source of methanol released during the interaction between MPTMS (APTMS) and hydrolyzed tetraethyl orthosilicate (TEOS). The methanol obtained in this way acts as a co-surfactant increasing the activity of ethanol released during hydrolysis of TEOS and enhancing the transformation of cylindrical SBA-15 towards the spherical MCF phase. Finally, it was shown that niobium species enhanced the oxidation of thiol groups in MPTMS towards sulfonic species and also affected slightly the morphology of the samples. The presence of niobium moieties did not influence, however, the formation of the pure MCFs mesostructured materials and their structural parameters.

Mesoporous silicate and niobiosilicate materials of SBA-15 type were prepared and post-synthesis modified with MPTMS, i.e. (3-mercaptopropyl)trimethoxysilane, followed by oxidation of thiol species. The samples obtained were characterised by different techniques (N2 adsorption/desorption, XRD, elemental and thermal analyses) and applied as catalysts in glycerol esterification with acetic acid. The focus was on the comparison of the role of niobium in the formation of sulphonic species and its stability in the post-synthesis modified materials (prepared within this work) with those, already published, prepared by one-pot synthesis method. The most important finding is that the presence of niobium in the SBA-15 structure improves the efficiency of –SH oxidation by hydrogen peroxide towards sulphonic species like in case of one-pot synthesised samples. However, contrary to the latter samples the presence of niobium does not increase the stability of the modifier (oxidized MPTMS). This has an impact on faster deactivation of samples prepared. Samples prepared with post-synthesis modification exhibit much higher activity in glycerol esterification.

The main objective of the present contribution is to analyze the effect of composition, coverage and Te doping in the surface composition and catalytic behavior of supported-nanoscaled MoVNb(Te)O catalysts. Different spectroscopy techniques combine to afford such objective. The composition of the surface species has been studied by Raman and UV–Vis spectroscopies, whereas it has been performed several pyridine adsorption experiments to quantify the number of acid sites on the surface of catalysts. The nature of reaction intermediates and the capability of the samples to adsorb them have been studied by FTIR spectroscopy combined with the adsorption of propene. The results have shown that tellurium induces several changes in the structure and catalytic properties of MoVNb catalytic materials, improving the reaction yield to the desired acrylic acid during the propane oxidation reaction.

The study presents a comparative analysis of catalytic properties of new Nb2SbVO10 ternary oxide against those of a mechanical mixture of single oxides and a mixture of single with binary oxide, all of the same chemical composition. Moreover, the material without antimony (Nb9VO25) was tested. Acid–base and redox properties were studied in the following test reactions: 2-propanol decomposition, acetonylacetone (AcOAc) cyclisation and methanol oxidation. The properties of ternary oxide and the mechanical mixture of single oxides are not significantly different. The main difference is in the generation of more active Lewis acid–base pairs in ternary oxide, which is demonstrated by the higher production of ether in the intermolecular dehydration of 2-propanol. Acidic/basic and redox properties of the oxide catalysts containing Nb, Sb, V, O (atomic ratio: 2:1:1:10) strongly depend on the presence of binary oxide, which significantly enhances the basicity of the catalysts. The highest basicity was found for pure binary oxide Nb9VO25 but this catalyst without Sb exhibits much lower activity in the transformation of both alcohols.

Design of base catalyst featuring large mesoporous surfaces allows performing base-catalysed reactions in the fields of production of perfumes. Post-synthesis grafting of organotrialkoxysilanes has effectively been applied to incorporate active organic functional groups onto the mesoporous silica surfaces. The novelty of our study is the use of mesoporous materials with different chemical compositions: silicate (MCM-41), aluminosilicate (AlMCM-41; Si/Al = 64) and niobosilicate (NbMCM-41; Si/Nb = 64) and consequently, different acidity, as supports for three aminopropylalkoxysilanes (APMS), [3-(2-aminoethylamino) propyl]trimethoxysilane (2APMS) and 3-[2-(2-aminoethylamino) ethylamino]propyltrimethoxysilane (3APMS). Isomerization of safrole to the corresponding thermodynamically stable isosafrole has been carried out on these amino-grafted MCM-41 materials. Maximum conversion of around 85% with a cis/trans ratio of 1/9 at 433 K in DMF as solvent was obtained. Isomerization is strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41 ≫ APMS/MCM-41. The nature of the amine chain is also responsible of the activity. The order of activity is APMS/AlMCM-41 > 2APMS/AlMCM-41 > 3APMS/AlMCM-41.

Non-acidic NaY, and acidic H-Beta and H-ZSM-5 with various Si/Al ratios were used as supports for gold loaded by deposition-precipitation method. Acidity of the pristine supports and Au/zeolites was estimated from adsorption of pyridine followed by FTIR spectroscopy measurements. NO selective reduction with propene (SCR-HC) was studied by the use of FTIR technique. Adsorption and co-adsorption of the reagents of NO SCR-HC (NO, C 3 H 6 and O 2 ) allowed a discussion of the reaction pathways. The catalytic behaviour of NaY referring to the intermediate formed was not significantly changed by gold modification and Au/NaY did not activate the partial oxidation of propene in the absence of NO. Au particles in Au/Na-Y play an important role in the total oxidation to CO 2 . The role of Bronsted acidity in Au/H-Beta and Au/H-ZSM-5 is on the oxidation of NO towards various intermediates (NO 2 − /NO 3 − , N 2 O 4 , NO + ) and their further interaction with propene, whereas gold species enhance this process by inducing formation of additional active complex (Au n + -NO). Moreover, gold species are responsible for the second reaction pathway via primary partial oxidation of propene to oxygenates and further reaction with NO and R-CN and R-NCO active intermediates as observed on Au/H-Beta and Au/H-ZSM-5.

This study deals with the influence of preparation method of SbVO x binary oxides and modification with niobium on the catalytic properties in the oxidation of methanol. The samples were prepared in the presence of a template by two different procedures with and without the template (Pluronic 123). The template-assisted synthesis leads to higher surface area and pore volume as well as smaller size particles of different shapes than those in the materials synthesised without the template. The rutile SbVO 4 phase dominates in all the catalysts studied. The preparation procedure determines the formation of the additives (V 2 O 5 or Sb 2 O 4 ) and the concentration of oxovanadium species on the catalyst surface. The presence of a small amount of Sb 2 O 4 acting as an electronic promoter in the oxidation of methanol is found when template-assisted synthesis is applied. Such a synthesis involves the formation of reducible oxovanadium species containing nucleophilic oxygen, playing an important role in the oxidation of methanol. Niobium loaded changes the selectivity towards DMM production. It has been found that by using different procedures of synthesis of binary SbVO x oxides and modification with niobium species, it is possible to obtain catalysts useful for the selective production of desired products (FA or MF or DMM) of methanol oxidation.

International audience; This study deals with the influence of V content on the catalytic properties of VxSiBEA zeolites in the oxidation of methanol. The samples are prepared following a postsynthesis method reported earlier (S. Dzwigaj, M.J. Peltre, P. Massiani, A. Davidson, M. Che, T. Sen, S. Sivasanker, Chem. Commun. (1998) 87). The incorporation of isolated mononuclear V(V) into the framework of SiBEA is evidenced by XRD, FTIR, diffuse reflectance UV-vis and NMR. It is found that, for low V content, V(V) ions are in pseudo-tetrahedral coordination only, either in nonhydroxylated (SiO)3VO or hydroxylated (SiO)2(OH)VO species in framework position. For higher V content, additional species appear in extraframework position with vanadium in octahedral coordination. FTIR investigations of pyridine adsorption show that strong Brønsted and Lewis acidic centres are present in SiBEA leading to dimethyl ether only, in methanol oxidation. Upon incorporation of vanadium into the BEA framework, Lewis acidic (V5+) and basic (O2−) centres are generated with simultaneous appearance of partial oxidation products mainly, whose total concentration increases with vanadium content. These results suggest that those centres are responsible for the oxidation activity of VxSiBEA zeolites. The selectivity toward formaldehyde increases with the amount of vanadium present as pseudo-tetrahedral hydroxylated (SiO)2(HO)VO species. This selectivity is suggested to be related to the moderate nucleophilicity of the basic vanadyl oxygen (VO) of (SiO)2(HO)VO species.