CeO2 is a promising catalyst for the HCl oxidation (Deacon process) in order to recover Cl2. Employing shape-controlled CeO2 nanoparticles (cubes, octahedrons, rods) with facets of preferential orientations ((100), (111), (110)), we studied the activity and stability under two reaction conditions (harsh: Ar:HCl:O2 = 6:2:2 and mild: Ar:HCl:O2 = 7:1:2). It turns out that both activity and stability are structure-sensitive. In terms of space time yield (STY), the rods are the most active particles, followed by the cubes and finally the octahedrons. This very same trend is reconciled with the complete oxygen storage capacity (OSCc), indicating a correlation between the observed activity STY and the OSCc. The apparent activation energies are about 50 kJ/mol for cubes and rods, while the octahedrons reveal an apparent activation energy of 65 kJ/mol. The reaction order in O2 is positive (0.26–0.32). Under mild reaction conditions, all three morphologies are stable, consistent with corresponding studies of CeO2 powders and CeO2 nanofibers. Under harsh reaction conditions, however, cubes and octahedrons are both instable, forming hydrated CeCl3, while rods are still stable. The present stability and activity experiments in the catalytic HCl oxidation reaction over shape-controlled CeO2 nanoparticles may serve as benchmarks for future ab initio studies of the catalyzed HCl oxidation reaction over well-defined CeO2 surfaces.Keywords: activity; CeO2; Deacon process; shape controlled particles; stability; structure sensitivity;

The epoxidation of styrene with hydrogen peroxide with higher selectivity to styrene oxide was carried out over lanthanum-doped MCM-48 (La-MCM-48) molecular sieves, in which aqueous NaOH solution was used to adjust the pH value of the reaction solution. The results show that the pH value of the reaction solution has a great influence on the catalytic performance of La-MCM-48 and the product distribution. When the pH value of the reaction solution was 11.5, the conversion of styrene reached 54.5% and the selectivity to styrene oxide was 98.8%. UV−vis and EPR spectroscopy was used to characterize the lanthanum species in the framework of La-MCM-48 and the peroxo-lanthanum species by H2O2 reacting with the lanthanum species. It has been found that the conversion of styrene has a close relationship with the amount of the peroxo-lanthanum species, and the selectivity to styrene oxide has a close relationship with the ratio of La(III)-superoxide species to La(III)-hydroperoxide species, which can be controlled by adjusting the pH value of the reaction solution.

Three series of Cr-based mixed oxides (Cr–Co, Cr–Fe, and Cr–Ni oxides) with high specific surface areas and amorphous textures were synthesized using a novel sol–gel method. These mixed oxides, in comparison to their pure metal oxide (CrOx, Co3O4, FeOx and NiO) counterparts, display enhanced performance for catalytic oxidation of low-concentration NO at room temperature. The best performing catalysts achieve 100% NO conversion for ∼30 h of operation at a high space velocity of 45 000 ml g−1 h−1. The amorphous structure was found to be critical for these catalysts to maintain high activity and durability. Control of the Cr/M (M = Co, Fe and Ni) molar ratio, nitrate precursor decomposition temperature and catalyst calcination temperature was key to the synthesis of these highly active catalysts.

•Co-Ce composite oxides were prepared by sol-gel method.•Ceria introduction modifies redox properties and chemical state of Ce-Co oxide catalysts.•Oxygen vacancies, lattice oxygen mobility and Co2+ species increased with Ce introduction.•Co(0.7)CeOx presented the best catalytic activity and stability for vinyl chloride abatement.A series of Co-Ce composite oxide catalysts with different molar ratio were prepared by the citrate sol-gel method and evaluated for the catalytic oxidation of vinyl chloride present in air, which was selected as a model reaction for chlorinated VOCs abatement from industrial exhaust. Numerous of characterization techniques including XRD, N2 sorption, Raman, H2-TPR, O2-TPD, NH3-TPD, XPS and HR-TEM were used to evaluate the influence of the physicochemical properties on the catalytic oxidation of 1000 ppm of vinyl chloride at a GHSV of 15,000 h−1.The presence of cerium in the cobalt oxides modified the redox properties and the chemical states of the Co-Ce composite oxide catalysts, increasing the presence of Co2+ species, the oxygen vacancies, and the oxygen mobility. Among the Co-Ce composite oxide catalysts, the one with a Co/(Ce + Co) molar ratio at 0.7 presented the highest catalytic activity and stability for the oxidation of vinyl chloride, which was related to the synergetic effect derived from the high reactivity on Co2+ sites and its further oxidation by surface active oxygen species.Download high-res image (150KB)Download full-size image

Ag-Cu-Cl/BaCO3 catalysts with different Cl and Cu loadings, prepared by the reduction deposition impregnation method, were investigated for gas-phase epoxidation of propylene by molecular oxygen and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and O2 temperature programmed desorption. Ag-Cu-Cl/BaCO3 catalyst with 0.036 wt% Cu and 0.060 wt% Cl exhibited the highest catalytic performance for gas-phase epoxidation of propylene by molecular oxygen. A propylene oxide selectivity of 83.7% and propylene conversion of 1.2% were achieved under the reaction conditions of 20% C3H6-10% O2-70% N2, 200 °C, 0.1 MPa and 3000 h−1. Increasing the Cl loading allowed Ag to ensemble easier, whereas changing the Cu loading showed little effect on Ag crystallite size. The appropriate Cl loading of Ag-Cu-Cl/BaCO3 catalyst can reduce the dissociation adsorption of oxygen to atomic oxygen species leading to the combustion of propylene to CO2, which benefits epoxidation of propylene by molecular oxygen. Excessive Cl loading of Ag-Cu-Cl/BaCO3 catalyst decreases propylene conversion and propylene oxide selectivity remarkably because of Cl poisoning. The appropriate Cu loading of Ag-Cu-Cl/BaCO3 catalyst is efficient for the epoxidation of propylene by molecular oxygen, and an excess Cu loading decreases propylene oxide selectivity because the aggregation of Cu species increases the exposed surfaces of Ag nanoparticles, which was shown by slight increases in atomic oxygen species adsorbed. The appropriate loadings of Cu and Cl of Ag-Cu-Cl/BaCO3 catalyst are important to strike the balance between molecular oxygen and atomic oxygen species to create a favorable epoxidation of propylene by molecular oxygen.The appropriate loadings of Cu and Cl of Ag-Cu-Cl/BaCO3 catalyst are important to the balance between molecular and atomic oxygen species, which benefits the epoxidation of propylene by molecular oxygen.Download high-res image (67KB)Download full-size image

•Supported LaMnOx on various oxide supports were synthesized by in situ citrate sol-gel method.•The formation of perovskite structure was confirmed on TiO2 and YSZ, but no observation on Al2O3 and CeO2.•The loading of LaMnOx oxides significantly improved the catalytic performances of oxide supports.•The main parameters of reducibility, acidity and surface adsorbed oxygen had an important role.LaMnO3 perovskites supported on Al2O3, TiO2, YSZ and CeO2 were prospectively synthesized by the in situ citrate sol-gel method. The physicochemical properties of these prepared materials were characterized by XRD, N2 sorption, H2-TPR, O2-TPD and NH3-TPD. The catalytic performances of these materials were evaluated in the catalytic oxidation of 1,2-dichloropropane (1,2-DCP), which was selected as a model reaction for chlorinated volatile organic compounds (CVOCs) abatement. It was shown that LaMnO3 perovskite structures were successfully formed over TiO2 and YSZ (LMO/TiO2 and LMO/YSZ), while just characteristic diffraction peaks assigned to oxide supports were observed over Al2O3 and CeO2 supported catalysts (LMO/Al2O3 and LMO/CeO2). The perovskites supported on TiO2 and YSZ presented higher catalytic activities than the perovskite alone. However, catalyst LMO/CeO2 exhibited an optimum catalytic behavior with high catalytic stability and durability for the oxidation of 1,2-DCP. Both the concentration of surface adsorbed oxygen species and the surface acidity were considered as the main factors responsible for the catalytic performances of these materials. Moreover, it was observed that oxygen mobility originated from the interaction of LaMnO3 and/or LaMnOx phases with oxide supports could be an additional parameter influencing the catalytic performance.Download high-res image (141KB)Download full-size image

•Novel amorphous CrOx-ZrO2 mixed oxide materials are synthesized.•100% NO conversion at ambient temperature for extended periods.•Deactivated catalysts can be fully regenerated with a simple heat treatment.•ZrO2 is found to stabilize Cr6+, the key redox sites in the mixed oxides.A series of novel CrOx-ZrO2 mixed oxide catalysts are prepared via a sol-gel method. Within a range of Cr/Zr atomic ratios, the mixed oxides maintain high surface area, homogeneous amorphous phases. As compared to CrOx-only catalysts formed using the same method, the addition of zirconia greatly enhances the catalytic performance for ambient-temperature, low-concentration NO oxidation. X-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR) analyses indicate an electronic effect of ZrO2 addition to the oxidation state of Cr. That is, ZrO2 addition induces an increase in surface concentrations of Cr6+. Rapid deactivation of a pre-reduced catalyst, coupled with the fact that a deactivated catalyst contains lower concentrations of surface Cr6+, provide rather strong evidence for a Mars-van Krevelen NO oxidation mechanism. Such a mechanism is also consistent with in situ DRIFTS observations.Download high-res image (107KB)Download full-size image

•Ag-CuCl2/BaCO3 catalyst was prepared by reduction-deposition-impregnation method.•Ag-CuCl2/BaCO3 catalyst with low CuCl2 doping exhibits better catalytic performance.•Epoxidation of propylene over Ag-CuCl2/BaCO3 catalyst follows Rideal-Eley mechanism.•Molecular oxygen species benefit epoxidation of propylene to propylene oxide.•Ag-based catalyst is deactivated by coke deposition and can be entirely regenerated.Ag-MClx/BaCO3 catalysts with different chloride promoters, prepared by reduction-deposition-impregnation method, were investigated for gas-phase epoxidation of propylene to propylene oxide (PO) by molecular oxygen. Ag-CuCl2/BaCO3 catalyst with 360 ppm of Cu and 400 ppm of Cl exhibits the best initial catalytic performance, in which PO selectivity of 71.2% and propylene conversion of 1.3% are achieved, but only PO selectivity of 13.9% is obtained at propylene conversion of 3.2% after reaction for 500 min. The catalytic reaction mechanism over Ag-CuCl2/BaCO3 catalyst follows Rideal-Eley mechanism, in which propylene in the gas phase reacts with molecular oxygen species adsorbed on the surface of Ag at the interface in close contact with CuCl2 to produce PO, and with atomic oxygen species adsorbed on the surface of Ag nanoparticles to produce CO2 and H2O. One oxygen atom of molecular oxygen species reacts with propylene to form a PO molecule, and the left insufficient oxygen atoms react with propylene to produce oxygen-containing intermediates and then to form coke deposition which covers the active sites and thus results in the catalyst deactivation. The deactivated Ag-CuCl2/BaCO3 catalyst can be completely regenerated by combustion of coke deposition and then impregnation with appropriate amount of Cl.

•V-MCFs were synthesized by co-condensation of TEOS and VTMS.•A-MCFs were prepared by copolymerization of V-MCFs with methacrolein.•A-MCFs retain the ultra-large and continuous 3D mesoporous structure.•PGA is immobilized covalently on the surface of A-MCFs.•PGA/A-MCFs shows high initial enzymatic activity and operational stability.Aldehyde-functionalized mesostructured cellular foams (A-MCFs) were successfully prepared by copolymerization of vinyl groups on the surface of vinyl-functionalized mesostructured cellular foams (V-MCFs) with methacrolein, and used for covalent immobilization of penicillin G acylase (PGA). Effects of functionalization with the organo-functional groups on the physicochemical properties of V-MCFs and A-MCFs, and the enzymatic activity and the operational stability of the immobilized PGA were investigated. A-MCFs-15% sample retains the characteristic ultra-large and continuous 3D mesoporous structure of MCFs with high surface area and large pore volume, which is beneficial for immobilization of PGA and diffusion of substrates and products, and thus results in high enzymatic activity of the immobilized PGA. PGA is immobilized covalently on A-MCFs sample via the reaction to produce Schiff’s base between the free amino groups of lysine residues of PGA and the aldehyde groups on the surface of A-MCFs, which greatly increases the operational stability of the immobilized PGA. PGA/A-MCFs-15% sample shows the initial enzymatic activity of 9531 U g−1 and retains 87% of its initial activity after recycled for ten times.

•Fe3O4/CHO-SiO2 sample with cannular structure was prepared by one-pot synthesis.•PGA was covalently immobilized on the surface of Fe3O4/CHO-SiO2 sample.•PGA/Fe3O4/CHO-SiO2 sample had high initial activity and operational stability.•PGA/Fe3O4/CHO-SiO2 sample was easily recycled by an external magnetic field.Aldehyde-functionalized mesoporous silica-Fe3O4 nanocomposites, one-pot synthesized by co-condensation of tetraethylorthosilicate and trimethoxysilylpropanal in presence of triblock copolymer of Pluronic P123, NaCl and Fe3O4 nanoparticles in the neutral solution, were characterized by SAXS, XRD, TEM, nitrogen sorption, FT-IR, TG, elementary analysis and magnetic susceptibility measurements, and investigated as the supports for covalent immobilization of penicillin G acylase (PGA). The results show that paramagnetic Fe3O4 nanoparticles were embedded among the cannular mesoporous silica layers and the aldehyde groups were condensed on the surface of mesoporous silica. PGA was covalently immobilized on these paramagnetic nanocomposites via the reaction to produce Schiff’s base between the free amino groups of lysine residues of PGA and the aldehyde groups on the surface of these nanocomposites. PGA immobilized on these paramagnetic nanocomposites had better operational stability and was easily recycled by an external magnetic field. The immobilized PGA had the initial activity of 6231 U g−1 and the operational stability of 91.0% of the initial activity after recycled for 10 times.Graphical abstract

•Cu-CeO2-Al2O3 catalyst has better catalytic performance.•Removal of residual sodium and water improves catalytic performance and stability.•Higher Cu dispersion and Cu surface area are advantageous.Cu-CeO2-Al2O3 catalysts were prepared by the co-precipitation method with different washing operations during the preparation process for the purpose of controlling the contents of the residual sodium and water in the catalyst precursors. Cu-CeO2-Al2O3 catalysts were characterized by ICP-AES, XRD, SEM, nitrogen sorption, N2O chemisorption, Raman spectroscopy and H2-TPR. Effects of the residual sodium and water in the catalyst precursor on the catalytic performance of Cu-CeO2-Al2O3 catalyst for gas-phase hydrogenation of maleic anhydride to γ-butyrolactone at atmospheric pressure, and the structure–activity relationships were investigated. The results show that the residual water and sodium in the form of Na2CO3 in the catalyst precursor lead to a decrease in Cu dispersion and Cu surface area, which is disadvantageous to the catalytic performance and stability. Washing step of the residual sodium in the catalyst precursor with the deionized water and then removing step of the residual water using azeotropy distillation shows a great improvement in the stability of Cu-CeO2-Al2O3 catalyst, in which 100% of conversion of maleic anhydride and 100% of selectivity to γ-butyrolactone were maintained for 12 h.

•Cu–ZnO–SiO2 catalyst showed better catalytic performance and stability.•Ba as a promoter can further improve greatly the catalyst stability.•Higher Cu surface area and ZnO dispersion can suppress the catalyst deactivation.Cu-ZnO-SiO2 (CZS) catalysts, prepared by the coprecipitation method, were investigated for gas-phase hydrogenation of maleic anhydride (MA) to γ-butyrolactone (GBL) at atmospheric pressure and characterized by XRD, N2O chemisorption, SEM and TGA. Effects of the compositions and the promoters on the catalytic performance and stability of CZS catalysts were investigated, in which CZS111 catalyst with the molar ratio of Cu:Zn:Si = 1:1:1 showed better catalytic performance and stability. The results show that the introduction of Ba as a promoter to CZS111 catalyst can further improve greatly the catalyst stability by increasing Cu surface area and ZnO dispersion with more additional adsorption sites for succinic anhydride (SA) to suppress the adsorption and polymerization of SA on the active sites of Cu0. The possible reaction pathways were proposed for gas-phase hydrogenation of MA to GBL, which could explain well the effect of Ba as a promoter on the stability of CZS111 catalyst.

Nanosized BaSO4-based mesoporous hybrid materials have been developed and identified as new efficient inorganic salt-based support systems for ultrastable gold nanoparticles in low-temperature CO oxidation.

Poly(4-styrenesulfonic acid) brush-grafted silica particles, synthesized by surface-initiated atom transfer radical polymerization, were employed as a reusable acid catalyst for dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water. The particles exhibited a high activity with the HMF yield of up to 31%, in contrast to 26% from the corresponding free homopolymer catalyst.

A general in situ growth method was successfully employed to prepare lanthanide phosphate–SiO2 mesostructured cellular foams (MCFs) (LnPO4–MCFs; Ln = La, Ce, and Eu; MCFs = SiO2). These heterostructured MCFs (LnPO4–MCFs) feature binary interpenetrating LnPO4 and silica frameworks, large surface areas, and uniform mesopore diameters. They were characterized by small-angle X-ray scattering, X-ray diffraction, nitrogen sorption, and transmission electron microscopy. The essence of this in situ growth synthesis lies in the controlled heterogeneous reaction of highly dispersed lanthanide oxides embedded in MCFs with phosphate ions in solution, leading to the formation of highly dispersed crystalline phosphate nanorods (nanocrystalline LnPO4) on the walls of MCFs. The resultant heterostructured LnPO4–MCFs were used as a novel support system for gold catalysts in CO oxidation at low temperatures. Gold precursor species can be readily introduced on LnPO4 nanophases of LnPO4–MCFs via a simple deposition–precipitation method. The resulting Au–LnPO4–MCF (2 wt% Au) catalysts exhibited high catalytic activities even below room temperatures. Because of the alteration of surface properties engineered by the in situ growth methodology and the strong interaction of metallic gold species with LnPO4, these catalysts are highly sinter-resistant. Although some cationic Au species are also present on the LnPO4–MCF surfaces, the metallic gold species are shown to be the key catalytic active sites for CO oxidation via in situ infrared spectroscopy.

Supported Ag-based bimetallic catalysts with low Ag loading of 3.0 wt%, prepared by the surfactant-protected colloidal method, were investigated for the epoxidation of propylene by molecular oxygen and characterized by UV–vis, XRD, TEM, XPS, and H2-TPR. Ag–Cu/BaCO3 bimetallic catalyst exhibits better catalytic performance, governed by the molar ratio of Ag/Cu, than other supported Ag-based bimetallic catalysts and monometallic catalysts for the epoxidation of propylene by molecular oxygen. The highest propylene oxide selectivity of 55.1% and the propylene conversion of 3.6% were achieved over Ag95–Cu5/BaCO3 bimetallic catalyst. XRD and TEM results show that a small quantity of Cu can effectively regulate the size of Ag crystallites to restrain their agglomeration. XPS results indicate that the presence of Cu can withdraw electrons from nearby Ag and thus make Ag electropositive, which is beneficial to produce more active sites where electrophilic oxygen species can be absorbed to increase the propylene oxide selectivity. H2-TPR results show that the reactivity and the amount of the oxygen species adsorbed on Ag surface can be regulated by the synergistic effect between Ag and Cu, which plays an important role in increasing the propylene oxide selectivity and the propylene conversion.Graphical abstractOver Ag95–Cu5/BaCO3 bimetallic catalyst with Ag loading of 3.0 wt%, the synergistic effect between Ag and Cu is beneficial to produce more active sites where electrophilic oxygen species can be absorbed and inhibit the reactivity of the oxygen species adsorbed on Ag surface, in which the propylene oxide selectivity of 55.1% and the propylene conversion of 3.6% were achieved.Highlights► Ag–Cu/BaCO3 bimetallic catalyst exhibits better catalytic performance. ► Cu can regulate the size of Ag crystallites to restrain their agglomeration. ► Cu can withdraw electrons from nearby Ag and make Ag electropositive. ► Synergistic effect between Ag and Cu is favorable to increase catalytic performance.

In this study, Al-MFI and B-MFI (Si/B = 100 and Si/B = 50) hollow fibres with nanocomposite architecture have been prepared on α-alumina by pore-plugging hydrothermal synthesis at 443 K for 89 h using a precursor clear solution with molar composition 1 SiO2: 0.45 TPAOH: 27.8 H2O: xH3BO3 (x = 0–0.02). The synthesized materials were characterized by XRD, SEM, ICP-AES and 29Si, 27Al- and 11B-MAS-NMR, revealing the genesis of well-intergrown materials with isomorphously substituted boron in the MFI unit cell. The pure ethylbenzene permeance within these membranes decreased in the order Al-MFI > B-MFI (Si/B = 50) > B-MFI (Si/B = 100). All the MFI materials were selective to p-xylene in the vapour permeation of ternary p-/m-/o-xylene mixtures and quaternary p-/m-/o-xylene/ethylbenzene model mixtures in the temperature range 400–650 K and for total feed vapour pressures lower than 4.5 kPa. The p-/m-xylene separation factor increased in the sense Al-MFI < B-MFI (Si/B = 100) ≈ B-MFI (Si/B = 50). The p-/m-xylene and p-/o-xylene separation factors, as well as p-xylene mixture fluxes, decreased with the ethylbenzene feed concentration, probably due to configurational entropy effects in the mixture adsorption patterns. The membranes showed however slightly preferential p-xylene permeation than ethylbenzene at low total aromatic vapour pressures despite the similar kinetic diameter of both molecules (5.8 vs. 6.0 Å), the B-MFI (Si/B = 50) material achieving a p-xylene/ethylbenzene separation factor as high as 5.Graphical abstractHighlights► We have prepared isomorphously substituted B-MFI (Si/B = 50–100) hollow fibres. ► The materials display a nanocomposite architecture instead of forming a thin film. ► The p-/m-xylene separation factor evolves: Al-MFI < B-MFI(Si/B = 100) ≈ B-MFI(Si/B = 50). ► B-MFI (Si/B = 50) membranes show p-xylene/ethylbenzene separation factors as high as 5.

Cu–CeO2–Al2O3 catalyst, prepared by co-precipitation method, was investigated for the gas-phase hydrogenation of maleic anhydride (MA) to γ-butyrolactone (GBL) at atmospheric pressure and the catalyst deactivation was also studied. Effects of catalyst composition, reaction temperature, and liquid hourly space velocity (LHSV) of raw material on the catalytic performance of Cu–CeO2–Al2O3 catalyst were investigated. The catalyst (molar ratio of Cu:Ce:Al = 1:1:2) showed better catalytic performance, in which both the conversion of MA and the selectivity of GBL kept 100% within two hours under the reaction conditions of 6 mL catalyst, 0.1 MPa, 220–280 °C, 30 mL min−1 H2, 0.6 h−1 LHSV of 20 wt.% MA/GBL. As for Cu–CeO2–Al2O3 catalyst, smaller crystallite size of Cu and higher Cu surface area are favorable to increase its catalytic performance. The deactivation of Cu–CeO2–Al2O3 catalyst is due to formation of the compact wax-like deposition on the catalyst surface, which is probably ascribed to the strong adsorption of succinic anhydride and then polymerization on the catalyst surface. The catalytic performance of the regenerated catalyst can be recovered completely by the regeneration method of N2–air–H2 stage treatment.Graphical abstractResearch highlights► Cu–CeO2–Al2O3 catalyst was prepared by co-precipitation method. ► The catalyst showed better catalytic performance. ► Small crystallite size of Cu and high Cu surface area of the catalyst are favorable. ► The catalyst deactivation is due to the compact wax-like surface deposition. ► The catalytic performance of the regenerated catalyst can be recovered completely.

Effects of concentration of chlorohydrocarbon and reaction time on the catalytic performance of 20% Ag–0.1% Y2O3–0.1% K2O/α-Al2O3 catalyst for the epoxidation of propylene by molecular oxygen were investigated, in which the role of chlorohydrocarbon in increasing selectivity of propylene oxide (PO) was characterized by XRD, SEM-EDS and XPS. With an increase in the concentration of chlorohydrocarbon in the feed gas, PO selectivity increased significantly and propylene conversion decreased remarkably and then the catalytic performance remained nearly constant when the concentration of chlorohydrocarbon was more than 125 ppm. PO selectivity increased from 46.8% to 75.6% and propylene conversion declined from 4.0% to 0.77% after 10 h induction period, and then the catalytic performance remained nearly constant for 140 h, under the reaction conditions of 245 °C, 0.1 MPa, GHSV of 2000 h−1, and 125 ppm 1,1,1-trichloroethane (TCE). A small amount of TCE could effectively control the surface morphology of the catalyst and restrain the agglomeration of Ag crystallites, in which TCE was dissociated on the surface of Ag crystallites to form AgCl and the coexistence of Ag and AgCl was favorable to increase PO selectivity. The presence of Cl could withdraw electrons from nearby Ag and thus make Ag electropositive, which was beneficial to produce more active sites where electrophilic oxygen species could be absorbed to increase PO selectivity. Y2O3 played a role of electron-type promoter that could strongly polarize electron cloud of nearby Ag, which made the absorbed oxygen species hold proper electrophilic character and then attack CC bond of propylene to produce PO.Graphical abstractHighlights► Concentration of chlorohydrocarbon had positive effect on PO selectivity. ► Ag-based catalyst showed better PO selectivity and stability with TCE in feed gas. ► TCE could effectively restrain the agglomeration of Ag crystallites. ► Coexistence of Ag and AgCl was favorable to increase PO selectivity. ► Presence of Cl could withdraw electrons from nearby Ag and thus make Ag electropositive.

One major drawback in the synthesis of zeolite membranes is the lack of reproducibility ascribed to the support quality. In this paper, a gas–liquid displacement technique was used prior to pore-plugging hydrothermal synthesis to evaluate the quality of hollow fibre supports in terms of pore size distribution of surface pores. Using these supports, four nanocomposite MFI-hollow fibre membrane families were identified, showing different gas/vapour separation performance. The effective MFI thickness of these membranes (0.6–1.2 μm) was computed from pure N2 and CO2 permeance using Maxwell–Stefan modelling, while their separation performance was evaluated in the separation of n-butane/H2, CO2/N2 and ternary xylene isomer mixtures. The MFI-alumina hollow fibres displaying the best quality corresponded to those synthesized using hollow fibres with surface pore size distributions centred at 0.2 μm, suggesting more efficient pore plugging. Grain boundaries between nearby zeolite crystals only appear to play a role in the case of xylene isomer separation.

In this study, Al-MFI and B-MFI hollow fibre membranes with nanocomposite architecture have been prepared by pore-plugging hydrothermal synthesis at 443 K for 89 h using a precursor clear solution with the molar composition 1 SiO2: 0.45 TPAOH: 27.8 H2O: (0.01 H3BO3). The structure and morphology of the synthesized materials has been analyzed by XRD, FTIR, ICP-AES, MAS-NMR, SEM and single gas permeation, reflecting in the case of B-MFI samples partial isomorphous substitution of framework Al and Si by boron (up to 1 B atom/uc). The separation performance of the membranes has been evaluated by n-butane/H2 and xylene isomer separations. The B-MFI hollow fibre membranes show improved separation performance towards p-xylene separation compared to conventional Al-based MFI-alumina hollow fibre membranes. Pre-adsorption of n-hexane or TMB has little effect on ternary xylene separation, suggesting the absence of intercrystalline mesoporous domains.

High quality nanocomposite B-MFI hollow fibers were successfully prepared by pore-plugging hydrothermal synthesis. The incorporation of boron into the MFI structure modifies the n-hexane/2,2-dimethylbutane vapor separation properties of the membranes, with the materials improving the n-hexane/2,2-dimethylbutane intrinsic separation factors of Al-MFI by a factor of 2 (up to a value of 200) at comparable conditions. The permeation performance of the membranes is essentially governed by a molecular sieving mechanism driven by preferential diffusion of n-C6 and configurational diffusion effects favoring n-hexane adsorption from n-hexane/2,2-dimethylbutane mixtures. A strong confinement scenario for surface diffusion of both n-hexane and 2,2-dimethylbutane seems to prevail.

Glucose isomerase (GI) from Streptomyces rubiginosus was immobilized covalently onto GAMM support prepared by our patented inverse suspension polymerization with glycidyl methacrylate (GMA), ally glycidyl ether (AGE), N,N′-methylene-bis(acrylamide) (MBAA), and acrylamide (MAA), and used for isomerization of glucose to fructose. Effects of immobilization conditions and reaction conditions on the activity of immobilized GI, the kinetic parameters, the operational stability, thermal stability and storage stability of immobilized GI were investigated. The optimum immobilization conditions were GI addition amount of 0.3 ml GI/g support, immobilization time of 24 h, and immobilization temperature of 25 °C. The optimum reaction conditions were pH value of reaction solution of 7.5 and reaction temperature of 65 °C. The activity of immobilized GI was 450 U/g (wet). Km and Vmax values of immobilized GI were 1.16 mol/L and 1.07 × 10−3 mol/L min, respectively. Immobilized GI onto GAMM support has better operational stability, thermal stability and storage stability, in which it retained 91% of its initial activity after recycled for 18 times and retained 97% of its initial activity after stored at 4 °C for six weeks. Therefore immobilized GI onto GAMM support was an excellent catalyst for isomerization of glucose to fructose.Graphical abstractGlucose isomerase immobilized covalently onto GAMM support, prepared by our patented inverse suspension polymerization, shows better activity of 450 U/g (wet) for isomerization of glucose to fructose and has better operational stability, thermal stability and storage stability.Download full-size imageHighlights► GAMM support was prepared by our patented inverse suspension polymerization. ► Glucose isomerase was immobilized covalently onto GAMM support. ► Immobilized glucose isomerase shows better activity for glucose isomerization.

•CHO-MCFs were prepared by post-synthetical functionalization of MCFs.•The aldehydepropyl groups were grafted successfully on the surface of CHO-MCFs.•The ultra-large 3D mesostructure of CHO-MCFs is beneficial for immobilization of PGA.•PGA immobilized covalently on CHO-MCFs increased the operational stability.The aldehydepropyl-functionalized mesostructured cellular foams (CHO-MCFs) were prepared by post-synthetical functionalization of MCFs with trimethoxysilylpropanal (TMSP), and used as efficient supports for immobilization of penicillin G acylase (PGA). The physicochemical properties of CHO-MCFs were characterized by SAXS, nitrogen sorption, TEM, elementary analysis, solid state 29Si MAS NMR, FT-IR spectroscopy and thermogravimetry. The results show that the aldehydepropyl groups have been grafted successfully on the surface of MCFs, and after functionalization, the BET surface area and pore volume of CHO-MCFs decrease, but the ultra-large and continuous 3D mesoporous structure of CHO-MCFs are retained to be beneficial for immobilization of PGA with large size and diffusion of substrates and products. PGA is immobilized covalently on CHO-MCFs via the reaction to produce Schiff's base between the free amino groups of lysine residues of PGA and the aldehyde groups on the surface of CHO-MCFs, which greatly increases the operational stability of the immobilized PGA with little activity loss due to the short-chain groups of aldehydepropyl grafted on the surface of CHO-MCFs. PGA/CHO-MCFs-10 shows the immobilization yield of 57.6%, the specific activity of 22.2 U/mg and the initial enzymatic activity of 8895 U/g, and retains 93.0% of its initial enzymatic activity after recycled for 10 times.Download full-size image

•LaMnO3 exhibited irreversible deactivation for the reaction.•Higher chlorinated organics were formed.•No coke and only traces of residual Cl species were detected on the used catalyst.•Specific surface area and reducibility are important factors for deactivation.•Mn oxidation state and surface oxygen species also affect the catalytic performance.A LaMnO3 perovskite oxide catalyst prepared by co-precipitation was evaluated for vinyl chloride (VC) oxidation over consecutive catalytic cycles and in steady-state conditions. The LaMnO3 catalyst exhibited relatively poor catalytic stability and durability, with the amount of chlorinated organic species increasing as catalytic activity decreased. Physicochemical properties were characterized by X-ray diffraction (XRD), N2 sorption, thermogravimetric and differential thermal analysis (TGA/DTA), energy disperse spectrocopy (EDS), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). Fresh and used catalysts presented a typical perovskite structure. No coke and only traces of residual chlorine species were detected on the used catalyst, indicating that coke formation and attack by chlorine were not the causes for deactivation. The used catalyst, however, presented lower specific surface area, low-temperature reducibility and surface oxygen mobility than the fresh one, suggesting that physicochemical and redox properties strongly influenced catalytic deactivation. Finally, a deactivation mechanism was proposed based on the Mn4+/Mn3+ redox cycle, and the formation of chlorinated by-products was inferred to be closely related to the presence of Cl species and catalyst deactivation.Download full-size image

The aminopropyl-functionalized silicas (APFS) with higher loading of amino groups was synthesized by the co-condensation of tetraethylorthosilicate (TEOS) and γ-aminopropyltriethoxysilane (APTES) in W/O microemulsion. Thus synthesized APFS was characterized by FT-IR spectroscopy, thermogravimetry, element analysis, solid state 13C and 29Si MAS NMR, TEM, and N2 sorption. The results show that the aminopropyl groups were condensed as the part of the silicate framework, and the amino contents could be adjusted by changing the volume ratio of APTES to TEOS in W/O microemulsion. APFS has been firstly used as the support for the immobilization of penicillin G acylase after activation with glutaraldehyde. Effects of the volume ratio of APTES to TEOS on the physico-chemical properties of APFS and the performance of immobilized penicillin G acylase were systematically investigated. Penicillin G acylase immobilized on APFS with the volume ratio of APTES/TEOS = 1/9 (1.77 mmol g−1 amino groups) behaves higher specific activity of 2759 IU g−1 and higher operational stability of 86% of the initial specific activity after recycled for 5 times, and the immobilization yield of 97%.

•NH2-Fe3O4 nanoparticles were successfully grafted on the outer surface of AMCFs.•PGA molecules were mainly immobilized covalently on the inner surface of PAMCFs.•PGA/PAMCFs show higher initial activity and operational stability.•PGA/PAMCFs are easily recycled by the magnetic field.Paramagnetic aldehyde-functionalized mesostructured cellular foams (PAMCFs), synthesized by grafting 3-aminopropyltriethoxysilane modified Fe3O4 (NH2-Fe3O4) nanoparticles with larger particle size than the window pore size of MCFs on the outer surface of aldehyde-functionalized mesostructured cellular foams (AMCFs), were investigated as efficient supports for immobilization of penicillin G acylase (PGA). The results show that NH2-Fe3O4 nanoparticles were successfully grafted on the outer surface of AMCFs and PGA molecules were mainly immobilized covalently on the inner surface of PAMCFs, which was because amino groups of NH2-Fe3O4 nanoparticles or PGA molecules reacted with aldehyde groups of AMCFs or PAMCFs to form imine bonds. PGA/PAMCFs-15 showed a rather high initial activity of 9563 U g−1 and retained 89.1% of its initial activity after recycled for 10 times. PGA/PAMCFs are easily recycled by magnetic field in order to replace tedious separation of high-speed centrifugation for mesoporous materials.Download full-size image

Nanosized BaSO4-based mesoporous hybrid materials have been developed and identified as new efficient inorganic salt-based support systems for ultrastable gold nanoparticles in low-temperature CO oxidation.

Poly(4-styrenesulfonic acid) brush-grafted silica particles, synthesized by surface-initiated atom transfer radical polymerization, were employed as a reusable acid catalyst for dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water. The particles exhibited a high activity with the HMF yield of up to 31%, in contrast to 26% from the corresponding free homopolymer catalyst.

A general in situ growth method was successfully employed to prepare lanthanide phosphate–SiO2 mesostructured cellular foams (MCFs) (LnPO4–MCFs; Ln = La, Ce, and Eu; MCFs = SiO2). These heterostructured MCFs (LnPO4–MCFs) feature binary interpenetrating LnPO4 and silica frameworks, large surface areas, and uniform mesopore diameters. They were characterized by small-angle X-ray scattering, X-ray diffraction, nitrogen sorption, and transmission electron microscopy. The essence of this in situ growth synthesis lies in the controlled heterogeneous reaction of highly dispersed lanthanide oxides embedded in MCFs with phosphate ions in solution, leading to the formation of highly dispersed crystalline phosphate nanorods (nanocrystalline LnPO4) on the walls of MCFs. The resultant heterostructured LnPO4–MCFs were used as a novel support system for gold catalysts in CO oxidation at low temperatures. Gold precursor species can be readily introduced on LnPO4 nanophases of LnPO4–MCFs via a simple deposition–precipitation method. The resulting Au–LnPO4–MCF (2 wt% Au) catalysts exhibited high catalytic activities even below room temperatures. Because of the alteration of surface properties engineered by the in situ growth methodology and the strong interaction of metallic gold species with LnPO4, these catalysts are highly sinter-resistant. Although some cationic Au species are also present on the LnPO4–MCF surfaces, the metallic gold species are shown to be the key catalytic active sites for CO oxidation via in situ infrared spectroscopy.

Three series of Cr-based mixed oxides (Cr–Co, Cr–Fe, and Cr–Ni oxides) with high specific surface areas and amorphous textures were synthesized using a novel sol–gel method. These mixed oxides, in comparison to their pure metal oxide (CrOx, Co3O4, FeOx and NiO) counterparts, display enhanced performance for catalytic oxidation of low-concentration NO at room temperature. The best performing catalysts achieve 100% NO conversion for ∼30 h of operation at a high space velocity of 45000 ml g−1 h−1. The amorphous structure was found to be critical for these catalysts to maintain high activity and durability. Control of the Cr/M (M = Co, Fe and Ni) molar ratio, nitrate precursor decomposition temperature and catalyst calcination temperature was key to the synthesis of these highly active catalysts.