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Click reaction is the most promising method for immobilization of ferrocene on SBA-15 for degradation of ciprofloxacin via photo-Fenton process.

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.

Gold catalysts based on SBA-15 and niobium-containing SBA-15 (NbSBA-15, to which niobium was introduced in one pot synthesis, and Nb2O5/SBA-15 prepared by post-synthesis impregnation of SBA-15) were doped with calcium species introduced before Au loading and were tested in gas-phase methanol oxidation with oxygen at different temperatures. Moreover, gold was loaded on the support prepared by the simultaneous post-synthesis modification of SBA-15 with a mixture of niobium(V) oxide and calcium oxide (Au/CaNbOx/SBA-15 sample). The structural/textural parameters (XRD, N2 adsorption/desorption), concentration of the surface species (XPS), as well as the surface acid–base properties (test reaction-2-propanol decomposition) of all catalysts were studied after the activation of materials in argon flow at 623 K. Moreover, the oxidation states and concentration of catalyst components were analyzed after methanol oxidation. FTIR study combined with methanol and oxygen adsorption allowed the proposal of the reaction pathways and estimation of the role of all the catalyst components. It has been indicated that the introduction of calcium dopant to gold catalysts significantly increased the activity in methanol oxidation because of the synergistic interaction between both gold calcium components. The presence of niobium directed the selectivity of the reaction. The active species, their concentration, and oxidation states of all modifiers did not change during the reaction of methanol oxidation. The role of chemisorption of the reaction intermediates has been considered in detail.

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.

The aim of this work was to gain insights into the role of manganese in MnSBA-15 support for gold in the base-free glucose oxidation with H2O2 using a microwave reactor. MnSBA-15 (manganese—acidity source) and SBA-15 (for comparison) were modified with Au (2.2 wt. %) and Cu (for comparison). The physicochemical properties of the catalysts were investigated by XRD, N2 ads/des, TEM, UV-vis, XPS, pyridine adsorption combined with FTIR, ATR-FTIR, and 2-propanol decomposition. The effects of the Mn presence in the support, Au NPs size that determines the number of active Au centers, and the Fermi energy (EF), together with the effects of the pore size, reaction temperature, and time on the activity and selectivity of the applied catalysts were assessed and discussed. It has been demonstrated that the presence of Mn generated Lewis acid centers which did not participate in glucose and H2O2 adsorption, and thus, were not directly involved in the reaction pathway. Both reagents were adsorbed on gold nanoparticles. H2O2 was decomposed to molecular oxygen which oxidized glucose to gluconic acid (50–90% of glucose conversion depending on the reaction time and ~100% selectivity). The presence of manganese in MnSBA-15 was responsible for increased Au NPs size and only slightly influenced the negative charge on gold particles. To achieve effective activity a compromise between the number of active gold species and the level of EF has to be reached (for 5.7 nm Au NPs).

The aim of this study was to get insight into the pathway of the acetaldehyde formation from ethanol (the rate-limiting step in the production of 1,3-butadiene) on Cu-SBA-15 and Cu-MnSBA-15 mesoporous molecular sieves. Physicochemical properties of the catalysts were investigated by XRD, N2 ads/des, Uv-vis, XPS, EPR, pyridine adsorption combined with FTIR, 2-propanol decomposition and 2,5-hexanedione cyclization and dehydration test reactions. Ethanol dehydrogenation to acetaldehyde (without and with oxygen) was studied in a flow system using the FTIR technique. In particular, the effect of Lewis acid and basic (Lewis and BrØnsted) sites, and the oxygen presence in the gas reaction mixture with ethanol on the activity and selectivity of copper catalysts, was assessed and discussed. Two different reaction pathways have been proposed depending on the reaction temperature and the presence or absence of oxygen in the flow of the reagents (via ethoxy intermediate way at 593 K, in ethanol flow, or ethoxide intermediate way at 473 K in the presence of ethanol and oxygen in the reaction mixture).

In this paper, the optimization of the synthesis of catalysts based on acidic mesoporous silica of the SBA-15 type by post-synthesis immobilization of 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) under increased pressure up to 20 bar is reported. Sample structures and composition were examined by XRD measurement, low-temperature N2 adsorption/desorption and elemental analysis. The catalytic activities of the materials obtained were determined in both gas and liquid phase processes, i.e., by esterification of acetic acid and glycerol dehydration, respectively. The optimum pressure for modification leading to the highest number of acidic sites was found to be 10 bar. The final material was very active and stable in liquid phase processes; however, the stability in the gas-phase process was unsatisfactory due to the loss of sulphonic species from the catalyst surface.

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.

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation, hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

Bifunctional catalysts—e.g., those with acidic and redox sites—are of particular importance, especially in the cascade processes, including the one-pot transformation of glycerol to acrylic acid. In this study, we explore one aspect of the preparation of a vanadium-containing catalyst, which can be further modified with 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS). The state of vanadium species loaded on mesoporous ordered silica of SBA-15 type was investigated before and after treatment with TPS, which can also be applied for the generation of acidic centers. Two vanadium sources, i.e., ammonium metavanadate and vanadium(IV) oxide sulfate, were applied to generate redox sites on SBA-15. The structure of materials obtained was analyzed using N2 adsorption/desorption and XRD measurements. For the estimation of the amount of vanadium and characterization of its state, the following techniques were applied: ICP, UV-Vis, XPS, ESR and FTIR combined with pyridine adsorption. The treatment of vanadium containing SBA-15 with TPS was found to lead to the oxidation of V4+ to V5+ and the partial removal of vanadium species, leading to a decrease in the number of penta-coordinated vanadium species. These features should be taken into account in the design of bifunctional catalysts with vanadium-active centers and SO3H acidic sites coming from TPS.

Formation of reactive oxygen species (ROS) via H2O2 activation is of vital importance in catalytic environmental chemistry, especially in degradation of organic pollutants. A new mixed niobium-cerium oxide (NbCeOx) was tailored for this purpose. A thorough structural and chemical characterization of NbCeOx along with CeO2 and Nb2O5 reference materials was carried out using TEM/STEM/EDS, SEM, XRD, XPS, EPR, UV-vis and N2 physisorption. The ability of the catalysts to activate H2O2 towards ROS formation was assessed on the basis of EPR and Raman measurements. Catalytic activity of the oxides was evaluated in degradation of methylene blue (MB) as a model pollutant. Very high activity of NbCeOx was attributed to the mixed redox-acidic nature of its surface, which originated from the synergy between Nb and Ce species. These two properties (redox activity and acidity) ensured convenient conditions for efficient activation of H2O2 and degradation of MB. The activity of NbCeOx in MB degradation was found 3 times higher than that of the commercial Nb2O5 CBMM catalyst and 240 times higher than that of CeO2. The mechanism of the degradation reaction was found to be an adsorption-triggered process initiated by hydroxyl radicals, generated on the surface via the transformation of O2-•/O22-.

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%.

Activity of gold supported catalysts strongly depends on the type and composition of support, which determine the size of Au nanoparticles (Au NPs), gold-support interaction influencing gold properties, interaction with the reactants and, in this way, the reaction pathway. The aim of this study was to use two types of zeolites: the three dimensional HBeta and the layered two-dimensional MCM-36 as supports for gold, and modification of their properties towards the achievement of different properties in oxidation of glucose to gluconic acid with molecular oxygen and hydrogen peroxide. Such an approach allowed establishment of relationships between the activity of gold catalysts and different parameters such as Au NPs size, electronic properties of gold, structure and acidity of the supports. The zeolites were modified with (3-aminopropyl)-trimethoxysilane (APMS), which affected the support features and Au NPs properties. Moreover, the modification of the zeolite lattice with boron was applied to change the strength of the zeolite acidity. All modifications resulted in changes in glucose conversion, while maintaining high selectivity to gluconic acid. The most important findings include the differences in the reaction steps limiting the reaction rate depending on the nature of the oxidant applied (oxygen vs. H2O2), the important role of porosity of the zeolite supports, and accumulation of negative charge on Au NPs in catalytic oxidation of glucose.

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.

The aim of this study was better understanding of surface properties of bimetallic (silver–platinum) catalysts and to verify if a very small addition of platinum (ca. 0.05 wt%) to silver (ca. 2.0 wt%) loaded on ordered mesoporous silica, SBA-15, would improve the catalytic properties of bimetallic Ag–Pt materials in selective oxidation of methanol to methyl formate. Ag–Pt catalysts were prepared by one-step and step-by-step procedures and the final Ag/Pt molar ratio in the respective samples was equal to 86 and 63. The catalysts were characterized after calcination and different activation treatments (in Ar and O2). X-ray diffraction, UV-vis and XP spectroscopy confirmed the lack of Ag–Pt alloy crystallites in the samples and also evidenced a higher resistance of silver oxide species to reduction upon activation in Ar flow in the presence of platinum promoter interacting with silver species. Methanol oxidation over the samples activated in Ar flow and in oxidizing flow (O2 + Ar) helped identify the role of each component in the bimetallic Ag–Pt catalyst in terms of activity and selectivity in the oxidation of methanol to methyl formate. A highly active bimetallic Pt/Ag/SBA-15 catalyst, selective to methyl formate and stable in methanol oxidation was constructed.

International audience; The aim of this study was to gain deeper insight into the factors determining the activity and selectivity of mono- (Au, Cu) and bimetallic (AuCu) catalysts supported on niobium pentoxide in photocatalytic oxidation of methanol. For this purpose, the prepared catalysts were comprehensively characterized with the use of XRD, nitrogen sorption, ICP-OES, UV-Vis, XPS, TEM and FTIR spectroscopy combined with in situ adsorption of probe molecules (methanol and pyridine). Photocatalytic activity of the materials was evaluated with the use of operando-IR system under irradiation with different light sources, i.e. UV and visible light. It was demonstrated that under UV irradiation, gold and/or copper dopants reduced the niobia activity but enhanced the reaction selectivity. Under visible light irradiation, the decoration of the niobia with bimetallic nanoparticles of gold and copper led to a synergic enhancement of the photocatalyst performance relative that of monometallic and non-doped niobia photocatalysts, tested under the same reaction conditions. It was also demonstrated that the selectivity over the bimetallic gold-copper/Nb2O5 catalyst was strongly affected by the nature of the light source: visible light irradiation promoted a total oxidation versus a partial oxidation of methanol under UV light irradiation. The relationship between the properties of the catalysts and their activity/selectivity considered in this work allowed explanation of differences in the photocatalysts behavior. It also permitted estimation of the role of individual catalyst components in the photocatalytic process. Moreover, monitoring of methanol photooxidation with the use of operando-IR system enabled estimation of reaction pathways and mechanism.

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.

Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).

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.

The idea of this work was to specify the conditions of alloying silver and platinum loaded on different silicas, i.e. commercial amorphous silica, MCF and NbMCF mesoporous cellular foams and to estimate the influence of the metal species on the activity and selectivity of the catalysts in the oxidation of methanol. For this purpose different amounts of both metals were used for achieving Ag/Pt molar ratios between 1.6 and 5.1. The obtained materials were characterized by nitrogen adsorption isotherms, XRD, TEM, XPS and UV-Vis. The measurements were performed after drying the materials at 333 K, followed by their calcination in air at 773 K and activation in argon or hydrogen flow at 673 K. Pt–Ag alloy was formed after calcination independently of the structure and composition of the support, if the Ag/Pt molar ratio achieved at least 2.5. On the majority of samples the alloy disappeared after activation in argon or hydrogen flow, with the exception of 0.5Pt2Ag/MCF material activated in argon. Structural properties of the support influenced the particle size of the alloy and in this way determined the stability of Pt–Ag alloy in this material. The role of the bimetallic alloy on the activity and selectivity of the catalysts in methanol oxidation is discussed in this paper. The metal species on the supports, sensitive to thermal activation in argon or hydrogen media, did not change during the catalytic oxidation of methanol.

We report herein an experimental study on the development of basicity on mesoporous silicas and metallosilicates (Nb- and Ce-) on SBA-15 and MCF porous structures. Our results demonstrated that the role of the catalyst structure (hexagonally ordered mesoporous SBA-15 vs. mesoporous cellular foam MCF), the effect of the amount and nature of metal in the supports (different acidic/redox properties), and the effect of the type of nitrogen-containing organic modifier (imidazole, triazole and aminotriazole) play an important role on the activity and selectivity in Knoevenagel condensation, which is a well-known probe reaction to determine the basicity of inorganic solids. We demonstrate that niobium Lewis acidity is determinant for the Knoevenagel condensation and, also, redox properties of cerium play an important role in the basicity. In fact, acid–base cooperation plays a positive role in promoting the Knoevenagel condensation via the ion-pair mechanism. These mesoporous silicas and metallosilicates are interesting catalysts for production of fine chemicals due to their thermal stability and controllable acid–base catalytic properties.

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.

Mesostructural cellular foam (MCF) materials that were modified by Zr, Nb, and Mo incorporation, followed by APTMS (3-aminopropyl-trimethoxysilane) grafting and gold loading were studied using the pair distribution function (PDF) technique. Measurements were focused on changes in gold crystallite sizes and on local geometry changes in the supports. Initially, ex situ prepared samples were investigated at different stages of synthesis and after catalytic oxidation of carbon monoxide. The crystallization and agglomeration of gold species as well as carbon monoxide oxidation were then tracked by in situ high energy diffraction measurements. The influence of metal type (Nb or Mo) and incorporation method in the MCF material on the agglomeration of metallic gold particles during increasing calcination temperature was determined. The structure of MCF materials was preserved during calcination and oxidation of CO and local symmetry of gold particles is not changed under CO oxidation conditions. In samples oxidiz...

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.

International audience; The stability of Ag-Pt systems: 13-atoms icosahedral cluster model (Ag13-nPtn) and 54-atoms (111) surface slab model (45Ag9Pt) have been systematically investigated by using Density Functional Theory within the generalized gradient approximation (DFT-GGA). Experimentally tested resistance of AgPt alloy nanoparticles supported on silica to decay upon temperature treatment (423 K-573 K in N2 flow) have shown to correlate with theoretical results. The stability of the clusters as a function of AgPt composition decreases with increasing content of Pt. The general stability trend of the AgPt alloy was maintained, in theory and experiment, for the Ag/Pt molar ratio of 1.6-5.1. Two particularly stable Ag/Pt compositions were revealed: 1.6 and 0.4. It was also found that surface location of platinum is responsible for stabilization of the Ag-Pt nanostructured alloy.

The focus of this chapter is on the modification of ordered mesoporous silica of different types with postsynthesis grafting of organosilanes (among others: amino-, imino-, thio-, sulfone-, phosphate-, carboxylic-organosilanes) or introduction of organosilane modifiers in one-pot synthesis of mesoporous silicas. The modified materials are discussed in the context of different aspects: (1) ways of preparation and characterization of hybrid materials; (2) catalysts containing basic (e.g., amine) or acidic (e.g., sulfone) active centers; (3) combination of amine species with BrOnsted acid sites, or Lewis acid sites, or redox species in bi- and trifunctional materials; and (4) the use of organosilane functionalization of mesoporous silica for further grafting of metal species. Finally, examples of the most spectacular catalytic application are given.