Time‐Resolved,In Situ DRIFTS/EDE/MS Studies on Alumina‐Supported Rhodium Catalysts: Effects of Ceriation and Zirconiation on Rhodium–CO Interactions

The effects of ceria and zirconia on the structure–function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al₂O₃) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ‐Al₂O₃ from [Ce(acac)₃] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)_x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ‐Al₂O₃. The structure–function correlations of ceria and/or zirconia‐doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier‐transform spectroscopy/energy‐dispersive extended X‐ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time‐resolved, in situ conditions. CeO_x and ZrO₂ facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ‐Al₂O₃ samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.     

Epoxidation of cyclohexene with H2O2 over efficient water‐tolerant heterogeneous catalysts composed of mono‐substituted phosphotungstic acid on co‐functionalized SBA‐15

A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH₂‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15 catalysts. Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst showed excellent catalytic performance in H₂O₂‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH₃‐SBA‐15 > Fe‐POM‐octyl‐NH₃‐SBA‐15 > Cu‐POM‐octyl‐NH₃‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH₃‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH₃‐SBA‐15, Co‐POM‐octyl‐NH₃‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH₃⁺ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.     

Structural Characterization of Alumina‐Supported Rh Catalysts: Effects of Ceriation and Zirconiation by using Metal–Organic Precursors

The effects of the addition of ceria and zirconia on the structural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al₂O₃) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposition of ceria on γ‐Al₂O₃ from Ce(acac)₃, and the rhodium metal is subsequently added, whereas method II is based on a controlled surface reaction technique, that is, the decomposition of metal–organic M(acac)_x (in which M=Ce, x=3 and M=Zr, x=4) on Rh/γ‐Al₂O₃. The structures of the prepared catalyst materials are characterized ex situ by using N₂ physisorption, transmission electron microscopy, high‐angle annular dark‐field scanning transmission election microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy (XPS), and X‐ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room temperature. By using ceriated and zirconiated precursors, a larger rhodium‐based metallic core fraction is obtained in comparison to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and reduction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows significant Rh? Cl interactions for Rh/Al₂O₃ and Rh/CeO_x/Al₂O₃ (method I) catalysts. After reaction with H₂/He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis affords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30–110 atoms), with the incorporation of zirconium providing the largest particle sizes.     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H₂O₂). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO₃ crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO₃ implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.     

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

Mesoporous SBA‐15 was synthesized and modified with 3‐chloropropyltrimethoxysilane and then used in immobilization of creatinine groups, which were employed to introduce Y³⁺ and Ce³⁺ to give rise to two novel yttrium and cerium catalysts: SBA‐15@Creatinine@M (M = Y and Ce). The structures of the SBA‐15@Creatinine@M catalysts were determined using various techniques. These catalysts offered outstanding catalytic performances in the oxidation of sulfides to sulfoxides and in the preparation of 5‐substituted 1H‐tetrazoles. An important characteristic of the SBA‐15@Creatinine@M catalysts is that they are very stable without a considerable decrease in their catalytic performance lasting seven cycles.     

Pd(OAc)2@SBA‐15/PrEn nanoreactor: a highly active,reusable and selective phosphine‐free catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous media

A series of ordered mesoporous organic–inorganic hybrid material was designed by using the amine‐functionalized SBA‐15 (PdX₂@SBA‐15/N_Y, Y = 1, 2) as solid support for palladium complexes. Among them, the Pd(OAc)₂/ethylenediamine complex encapsulated into SBA‐15 (Pd(OAc)₂@SBA‐15/PrEn or Pd(OAc)₂@SBA‐15/PrNHEtNH₂) exhibits higher activity and selectivity toward Suzuki cross‐coupling reaction under aerobic conditions and water solvent mixture. The SBA‐15/PrEn supported palladium pre‐catalyst could be separated easily from reaction products and used repetitively several times, showing its superiority over homogeneous catalysts for industrial and chemical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Ordered mesoporous SBA‐15/PrSO3Pd and SBA‐15/PrSO3PdNP as active,reusable and selective phosphine‐free catalysts in CX activation Heck coupling process

The incorporation of sulfonate into mesoporous SBA‐15 molecular sieves as ligands for palladium ions was used. Then SBA‐15/PrSO₃Pd and SBA‐15/PrSO₃Pd_NP were prepared and applied for the Heck arylation reaction of conjugate alkenes with aryl halides, to afford corresponding cross‐coupling products under phosphine‐free aerobic conditions with good to excellent yields. These supported palladium pre‐catalysts could be separated easily from reaction products and reused several times, showing superiority over homogeneous catalysts for industrial and chemical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Metathesis of 1‐Butene to Propene over Mo/Al2O3@SBA‐15: Influence of Alumina Introduction Methods on Catalytic Performance

A series of Mo‐based catalysts for 1‐butene metathesis to propene were prepared by supporting Mo species on SBA‐15 premodified with alumina. The effects of the method of introduction of the alumina guest to the host SBA‐15 on the location of the Mo species and the corresponding metathesis activity were studied. As revealed by N₂ adsorption isotherms and TEM results, well‐dispersed alumina was formed on the pore walls of SBA‐15 if the ammonia/water vapor induced hydrolysis (NIH) method was employed. The Mo species preferentially interacted with alumina instead of SBA‐15, as evidenced by X‐ray photoelectron spectroscopy, time‐of‐flight secondary‐ion mass spectrometry, and IR spectroscopy of adsorbed pyridine. Furthermore, new Brønsted acid sites favorable for the dispersion of the Mo species and low‐temperature metathesis activity were generated as a result of the effective synergy between the alumina and SBA‐15. The Mo/Al₂O₃@SBA‐15 catalyst prepared by the NIH method showed higher metathesis activity and stability under the conditions of 120 °C, 0.1 MPa, and 1.5 h^?1 than catalysts prepared by other methods.     

Revealing the Dynamic Structure of Complex Solid Catalysts Using Modulated Excitation X‐ray Diffraction

X‐ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach, time‐resolved high‐energy XRD is able to provide the detailed redox dynamics of palladium nanoparticles with a diameter of 2 nm in 2 wt % Pd/CZ (CZ=ceria–zirconia), which is a difficult sample for extended X‐ray absorption fine structure (EXAFS) measurements because of the cerium component. The temporal evolution of the Pd(111) and Ce(111) reflections together with surface information from synchronous diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements reveals that Ce maintains Pd oxidized in the CO pulse, whereas reduction is detected at the beginning of the O₂ pulse. Oxygen is likely transferred from Pd to Ce³⁺ before the onset of Pd re‐oxidation. In this context, adsorbed carbonates appear to be the rate‐limiting species for re‐oxidation.     

Catalytic Hydrodechlorination of 1,2,4,5‐Tetrachlorobenzene over Various Supports Loaded Palladium Catalysts

Water pollution by polychlorinated aromatic hydrocarbons has always been a global issue. In this work, we reported a synthesis of supported palladium catalysts Pd/C, Pd/CeO₂, Pd/SBA‐15, Pd/ZrO₂,Pd/SiO₂, and Pd/Al₂O₃ as well as their catalytic activities on hydrodechlorination (HDC) of 1,2,4,5‐tetrachlorobenzene (TeCB). These Pd catalysts were characterized by Brunauer‐Emmett‐Teller (BET) specific surface area, Transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy Dispersive X‐ray Fluorescence (EDXRF), CO‐chemisorption, and H2‐temperature programmed reduction (H2‐TPR) analysis. Pd/C, Pd/CeO₂ and Pd/SBA‐15 catalysts showed relatively high catalytic activities. The catalytic activities were associated with dispersion of Pd, metal surface area, and reaction temperature, etc.     

Bismuth‐Containing SBA‐15 Mesoporous Silica Catalysts for Solvent‐Free Liquid‐Phase Oxidation of Cyclohexane by Molecular Oxygen

Bismuth (Bi)‐containing SBA‐15 mesoporous silica catalysts, Bi/SBA‐15, with different Bi loadings were synthesized by a direct hydrothermal method. The materials were characterized in detail by various techniques. Powder‐X‐ray‐diffraction (PXRD), N₂‐adsorption/desorption, and transmission‐electron‐microscopic (TEM) analyses revealed that the well‐ordered hexagonal structure of SBA‐15 is maintained after Bi incorporation. Diffuse‐reflectance UV/VIS, Raman, and X‐ray photoelectron spectroscopy (XPS) showed that the incorporated Bi‐atoms are highly dispersed, most of them entering the internal surface of SBA‐15. The new, very stable catalysts were found to be highly efficient for the oxidation of cyclohexane in a solvent‐free system, molecular oxygen (O₂) being used as oxidant.     

SBA‐15‐supported N‐coordinate ruthenium(II) materials bearing sulfonamide‐type ligands: Effect of ligand backbones on catalytic transfer hydrogenation of ketones and aldehydes

[RuLCl(p ‐cymene)] (L = N ‐arylsulfonylphenylenediamine) complexes ( 2 _{a – d} ) were synthesized from the reaction between [Ru(p ‐cymene)Cl₂]₂ and ligand. Additionally, SBA‐15–[RuLCl(p ‐cymene)] derived catalysts ( 3 _{a – d} ) were successfully immobilized onto mesoporous silica (SBA‐15) by an easily accessible approach. The structural elucidations of 2 _{a – d} and 3 _{a – d} were carried out with various methods such as ¹H NMR, ¹³C NMR and infrared spectroscopies, elemental analysis, thermogravimetric/differential thermal analysis, nitrogen adsorption–desorption and scanning electron microscopy/energy‐dispersive X‐ray analysis. The Ru(II) complexes and materials were found to be highly active and selective catalysts for the transfer hydrogenation (TH) reaction of aldehydes and ketones. The influence of various 1,2‐phenylenediamines on the reactivity of the catalysts (complexes or materials) was studied and the catalysts ( 2 _d and 3 _d ) with a 4,5‐dichlorophenylenediamine substituent showed the best activity (the maximum turnover frequencies are 2916 and 2154 h⁻¹ for TH of 4‐fluoroacetophenone, and 6000 and 4956 h⁻¹ for TH of 4‐chlorobenzaldehyde).     

Effect of inorganic oxide supports on the activity of chromium‐based catalysts in ethylene trimerization

Novel heterogeneous catalysts were prepared using immobilization of bis(2‐decylsulfanylethyl)amine–CrCl₃ (Cr‐SNS‐D) on various supports, namely commercial TiO₂, Al₂O₃ and magnetic Fe₃O₄@SiO₂ nanoparticles, to yield solid catalysts denoted as support@Cr‐SNS‐D. The structure of the catalysts was confirmed on the basis of spectroscopic analyses, N₂ adsorption–desorption and inductively coupled plasma (ICP) analysis. The surface areas of Al₂O₃@Cr‐SNS‐D, Fe₃O₄@SiO₂@Cr‐SNS‐D and TiO₂@Cr‐SNS‐D catalysts were determined to be 70, 23 and 41 m² g^?1, respectively. A decrease in surface area from that of the supports clearly establishes accurate immobilization of Cr‐SNS‐D catalyst on the surface of the parent carriers. The loading of Cr was determined to be 0.02, 0.16 and 0.11 mmol g^?1 for Cr‐SNS‐D supported on TiO₂, Al₂O₃ and Fe₃O₄@SiO₂, respectively, using ICP analysis. After preparation and full characterization of the catalysts, ethylene trimerization reaction was accomplished in 40 ml of dry toluene, at 80°C and 25 bar ethylene pressure and in the presence of methylaluminoxane (Al/Cr = 700) within 30 min. The supported chromium catalysts were found to be efficient and selective for the ethylene trimerization reaction. The highest activity (74 650 g_1‐hexene g_Cr^?1 h^?1), as well as no polyethylene formation during reaction processes, was observed when TiO₂ was used as the catalyst support.     

N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

Magnetic mesoporous silica was prepared via embedding magnetite nanoparticles between channels of mesoporous silica (SBA‐15). The prepared composite (Fe₃O₄@SiO₂‐SBA) was then reacted with 3‐chloropropyltriethoxysilane, sodium imidazolide and 2‐bromopyridine to give 3‐(pyridin‐2‐yl)‐1H‐imidazol‐3‐iumpropyl‐functionalized Fe₃O₄@SiO₂‐SBA as a supported pincer ligand for Pd(II). The functionalized magnetic mesoporous silica was further reacted with [PdCl₂(SMe₂)₂] to produce a supported N‐heterocyclic carbene–Pd(II) complex. The obtained catalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, Brunauer–Emmett–Teller surface area measurement and X‐ray diffraction. The amount of the loaded complex was 80.3 mg g^?1, as calculated through thermogravimetric analysis. The formation of the ordered mesoporous structure of SBA‐15 was confirmed using low‐angle X‐ray diffraction and transmission electron microscopy. Also, X‐ray photoelectron spectroscopy confirmed the presence of the Pd(II) complex on the magnetic support. The prepared magnetic catalyst was then effectively used in the coupling reaction of olefins with aryl halides, i.e. the Heck reaction, in the presence of a base. The reaction parameters, such as solvent, base, temperature, amount of catalyst and reactant ratio, were optimized by choosing the coupling reaction of 1‐bromonaphthalene and styrene as a model Heck reaction. N‐Methylpyrrolidone as solvent, 0.25 mol% catalyst, K₂CO₃ as base, reaction temperature of 120°C and ultrasonication of the catalyst for 10 min before use provided the best conditions for the Heck cross‐coupling reaction. The best results were observed for aryl bromides and iodides while aryl chlorides were found to be less reactive. The catalyst exhibited noticeable stability and reusability.     

Cobalt(II) acetylacetonate complex immobilized on aminosilane‐modified SBA‐15 as an efficient catalyst for epoxidation of trans‐stilbene with molecular oxygen

From environmental and economic points of view, it is highly desirable to develop a clean and efficient catalytic process to produce epoxides. An attractive approach is to use a solid, recyclable catalyst and molecular oxygen as the oxidant without any sacrificial reductant or other additives. Nonetheless, the catalysts reported up to now still cannot balance catalytic activity with epoxide selectivity. It is of great importance to explore novel catalysts with both high activity and selectivity for the epoxidation of olefins. In this work, cobalt(II) acetylacetonate (Co(acac)₂) was covalently bonded to the silica surface of SBA‐15 molecular sieve by multi‐step grafting using 3‐aminopropytrimethoxysilane (APTS) as coupling agent. Characterizations with nitrogen physisorption, X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis suggested that the metal complex was successfully immobilized on the aminosilane‐modified SBA‐15 surface and the channel structure remained intact. The synthesized Co(acac)₂APTS@SBA‐15 catalyst was used in the epoxidation of trans‐stilbene (TS) with molecular oxygen. Compared to the sample prepared by the impregnation method as well as Co(acac)₂ solutions under the same reaction conditions, the Co(acac)₂ immobilized catalyst exhibited remarkably higher TS conversion and trans‐stilbene oxide (TSO) selectivity. An increase in TS conversion with Co content was observed when the Co loading was lower than 0.70% and the 0.70Co(acac)₂APTS@SBA‐15 sample exhibited the best catalytic performance. Up to 50.1% of TS conversion could be achieved within 6 h, affording TSO selectivity as high as 96.7%. The superior catalytic performance of this particular catalyst is attributed to the high activity of the immobilized Co(acac)₂ species on SBA‐15. Copyright © 2016 John Wiley & Sons, Ltd.     

Water Adsorption and Dissociation on Ceria‐Supported Single‐Atom Catalysts: A First‐Principles DFT+U Investigation

Single‐atom catalysts have attracted wide attention owing to their extremely high atom efficiency and activities. In this paper, we applied density functional theory with the inclusion of the on‐site Coulomb interaction (DFT+U) to investigate water adsorption and dissociation on clean CeO₂(111) surfaces and single transition metal atoms (STMAs) adsorbed on the CeO₂(111) surface. It is found that the most stable water configuration is molecular adsorption on the clean CeO₂(111) surface and dissociative adsorption on STMA/CeO₂(111) surfaces, respectively. In addition, our results indicate that the more the electrons that transfer from STMA to the ceria substrate, the stronger the binding energies between the STMA and ceria surfaces. A linear relationship is identified between the water dissociation barriers and the d band centers of STMA, known as the generalized Brønsted–Evans–Polanyi principle. By combining the oxygen spillovers, single‐atom dispersion stabilities, and water dissociation barriers, Zn, Cr, and V are identified as potential candidates for the future design of ceria‐supported single‐atom catalysts for reactions in which the dissociation of water plays an important role, such as the water–gas shift reaction.     

Characterization and Dehydrogenation Activity of SBA-15 and HMS Supported Chromia Catalysts

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Catalytic Gas‐phase Fluorination of Hexachlorobutadiene to 1,2‐Dichlorotetrafluorocyclobutene over Cr/Zn‐based Catalysts

In this paper, the gas‐phase fluorination of hexachlorobutadiene (HCBD) to synthesize 1,2‐dichlorotetrafluorocyclobutene (DTB) was carried out over a series of Cr/M/Zn catalysts (M = Ni, Co, Cu, In, Al). The influence of prefluorination by different fluorinating agents (HF, 95%HF + 5%Cl₂, 95%HF + 5%O₂, CF₂O, CF₂Cl₂) on catalytic performance of Cr/Co/Zn sample was also investigated. The addition of prompters to the Cr/Zn catalyst improved remarkably its catalytic properties. The Cr/Ni/Zn catalyst exhibited the best catalytic activity (1.318 mmol/h/g) at 390 °C and the Cr/Co/Zn catalyst showed the best DTB selectivity (42.5%) at 350 °C. Compared to that of gaseous HF, the catalytic performance of the Cr/Co/Zn catalyst after treatment by HF + O₂ and CF₂O increased considerably, whereas for HF + Cl₂ and CF₂Cl₂ it showed little effect. In order to identify the different species (Cr─O, Cr─F, CrO _xF _y) present on catalysts’ surface and determine their exact role, these catalysts before and after the reaction were characterized by X‐ray photoelectron spectroscopy. It was found that the concentration of the various species was responsible for the activity and lifetime of catalysts. Moreover, a possible reaction route is proposed based upon the product distribution. The most feasible formation pathway of DTB proceeded via the cyclization of C₄Cl₄F₂ or C₄Cl₃F₃ to yield c‐C₄Cl₄F₂ and c‐C₄Cl₃F₃ followed by further the Cl/F exchange.     

Immobilization of cerium (IV) and erbium (III) in mesoporous MCM‐41: Two novel and highly active heterogeneous catalysts for the synthesis of 5‐substituted tetrazoles,and chemo‐ and homoselective oxidation of sulfides

Two well‐ordered 2D ‐ hexagonal cerium (IV) and erbium (III) embedded functionalized mesoporous MCM ‐ 41(MCM‐41@Serine/Ce and MCM ‐ 41@Serine/Er) have been developed via functionalization of mesoporous MCM ‐ 41. The surface modification method has been used in the preparation of serine‐grafted MCM ‐ 41 and led to the development of MCM‐41@Serine. The reaction of MCM‐41@Serine with Ce (NH₄)₂(NO₃)₆·2H₂O or ErCl₃·6H₂O in ethanol under reflux led to the organization of MCM‐41@Serine/Ce and MCM‐41@Serine/Er catalysts. The structures of these catalysts were determined using scanning electron microscopy, mapping, energy‐dispersive X‐ray spectroscopy, Fourier transform‐infrared, thermogravimetric analysis, X‐ray diffraction, inductively coupled plasma, and Brunauer–Emmett–Teller analysis. These MCM‐41@Serine/Ce and MCM‐41@Serine/Er catalysts show outstanding catalytic performance in sulfides oxidation and synthesis of 5‐substituted tetrazoles. These catalysts can be recycled for seven repeated reaction runs without showing a considerable decrease in catalytic performance.