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Direct epoxidation of propylene (C 3 H 6) with hydrogen (H 2) and oxygen (O 2) over Au/TS-1 catalyst was promising way for the synthesis of propylene oxide (PO). However, high selectivity of PO (>95 %) and conversion of C 3 H 6 (>5 %) cannot be achieved at the same time. The industrialization process was severely restricted. In this paper, Au/TS-1 catalysts were synthesized by deposition precipitation method with alkali metal promoter. And alkaline gases and silane coupling post-treatment were performed to promote the catalytic activity. The prepared samples exhibited a much better C 3 H 6 conversion (6.5 %) and PO selectivity (95.1 %) compared with general catalyst using normal synthetic technology. Cs 2 CO 3 was beneficial to increasing Au nanoparticles uptake efficiency. Both NH 3 and triethoxyvinylsilane post-treatment were good for smaller and more uniform loading of Au nanoparticles. The decreasing in surface hydroxyl density effectively alleviated the occurrence of PO ring opening isomerization. The increased hydrophobicity of TS-1 surface was conducive to the rapid desorption of generated PO and significantly increased PO selectivity. Multiple pretreatment was also favorable for extending the lifetime of Au/TS-1 catalyst. [Display omitted] • Multiple pretreatment exhibit better loading of Au nanoparticles both on size and distribution. • Charming C 3 H 6 conversion (6.5 %) and PO selectivity (95.1 %) were obtained. • PO ring opening isomerization or oligomerization was effectively inhibited. • Lifetime of Au/TS-1 catalyst extended obviously after multiple pretreatment. [ABSTRACT FROM AUTHOR]

Stable and efficient Au-supported titanium silicalite-1 (TS-1) catalysts are essential for the direct epoxidation of propylene (DEP) using O 2 and H 2. But the deposition-precipitation method for Au/TS-1 contains low Au capture efficiency and rapid deactivation rate. Herein, Au/TS-1-B (uncalcined TS-1) catalysts were synthesized through a NaBH 4 reduction method. The impact of H 2 -thermal-pretreatment on DEP activities was studied. H 2 -pretreatment can enhance propylene oxide selectivity, shorten activation time and reduce deactivation rate of catalyst. Organic-templates on the surface of TS-1-B and stabilizers coated on Au-nanoparticles can be partially removed under H 2 -treatment, thus exposing more active sites for Au and Ti and facilitating their interactions. Furthermore, more porous structures with reduced acid sites and enhanced surface hydrophobicity of pretreated catalyst can promote DEP reaction. Solid stability in TS-1-B, high Au utilization resulting from the reduction method, and favorable modifications through H 2 -thermal treatment contribute to the exploration of more robust DEP catalyst performance. [Display omitted] • A DEP catalyst with high Au capture efficiency was prepared via NaBH 4 reduction. • H 2 pretreatment increases the PO selectivity and catalyst stability. • Enhanced Au-Ti interactions contribute to the dimension control of Au sols. • Surface configuration changes affect the DEP reactions [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Converting renewable resources to a chemical that is a precursor for making fuels. • The catalytic conversion of methyl ethyl ketone to butene over several supported Cu catalysts as bifunctional catalysts. • The high selectivity (above 97%) to produce butene from MEK can be achieved over Cu supported on zeolite Y sodium. Abstract The direct conversion of methyl ethyl ketone (MEK) to butene over supported copper catalysts was investigated in a fixed bed reactor over Cu-Al 2 O 3 , Cu-zeolite Y sodium (Cu-ZYNa) and Cu-zeolite Y hydrogen (Cu-ZYH). In this reaction, MEK is hydrogenated to 2-butanol over metal sites which is further dehydrated on acid sites to produce butene. Experimental results showed that the selectivity of butene was the highest over Cu-ZYNa, and it was improved by finding the optimum reaction temperature, hydrogen pressure and the percentage of copper loaded on ZYNa. The highest selectivity of butene (97.9%) was obtained at 270 °C and 20 wt% Cu-ZYNa. Over Cu-Al 2 O 3 , the selectivity of butenes was less than Cu-ZYNa since subsequent hydrogenation of butene occurred to produce butane. It was also observed that with increasing H 2 /MEK molar ratio, butane selectivity increased. However, when this ratio was decreased, hydrogenation of butene was reduced, but dimerization to C 8 alkenes and alkane began to be favored. The main products over 20% Cu-Al 2 O 3 were butene and butane, and a maximum selectivity of butene (87%) was achieved at an H 2 /MEK molar ratio of five. The lowest selectivity of butene was obtained using Cu-ZYH, reaching ∼40%. All catalysts were characterized by (NH 3 -TPD), (CO 2 -TPD), XPS and TPR to probe catalyst acidity, basicity and the reducibility of Cu loaded on the supports. It was found that the amount of acidity in Cu-ZYH is much higher than in Cu-ZYNa. This could have caused the selectivity of butene to decrease as a result of dimerization, oligomerization and cracking reactions. [ABSTRACT FROM AUTHOR]

A series of bimetallic Zn-Co catalysts before and after calcination were prepared by simple MOFs template methods. The effects of calcination on their structures were investigated by XRD, FT-IR, TPD, XPS and EPR characterization methods, and their catalytic performances were compared in the cycloaddition reactions of CO 2 and propylene oxide and acylation reactions of anisole and acetyl chloride, respectively. The results show that uncalcined ZnCo2-MOFs catalyst has excellent catalytic performance for cycloaddition reaction due to the presence of acid-base synergism, whereas the strong acidity of calcined ZnCo2O X catalyst is very favorable for acylation reaction. This is due to the fact that calcination changes the structure of ZnCo2-MOFs catalyst, causes charge migration on the surface and results in the conversion of lattice oxygen to oxygen vacancies, which brings a large difference in the acidity and basicity of catalysts. [Display omitted] • A series of Zn-Co bimetallic catalysts via a simple MOFs template method were obtained. • These catalysts before and after calcination exhibit excellent results for two different reactions. • Before calcination, acidity comes from metal sites and basicity comes from imidazole N as well as lattice oxygen. • After calcination, strong Lewis acidity derived from metal sites as well as oxygen vacancies. • Innovative linking of changes in acidity and basicity to structural differences brought about by calcination. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Y 2 O 3 –Inserted Co-Pd catalysts were prepared for reductive amination. • The catalysts led to 99% PEA yield from PPG via a facile one-pot synthesis. • The Y 2 O 3 -inserted catalysts inhibit Co 3 N but promote hydrogenation of imine. • Basicity of Y 2 O 3 hinders NH 3 access into the cobalt surface of the catalysts. Abstract Cobalt-based catalysts having different base strengths were prepared by controlling the amount of yttrium oxide (Y 2 O 3). These catalysts were used for the facile one-pot synthesis of polyetheramine (PEA) from polypropylene glycol (PPG) through reductive amination. It is noticed that high hydrogen partial pressures up to 40 bar inhibit the formation of cobalt nitride and lead to a high PEA yield although it has been known that dehydrogenation from alcohol to ketone is the rate-determining step. The Y 2 O 3 -inserted Co-Pd/Molecular sieve13X catalyst also showed high activity toward PEA even at low hydrogen partial pressure. Y 2 O 3 played a crucial role in giving basicity to the catalyst, which not only prevents the formation of cobalt nitride but also promotes hydrogenation of imine to amine at a wide range of H 2 pressure. Thus Y 2 O 3 inserted Co-Pd/Molecular sieve 13X provides unique performance toward enhancing the PEA yield while suppressing the catalyst deactivation caused by the cobalt nitride formation. [ABSTRACT FROM AUTHOR]

The base-catalyzed, gas-phase epoxidation of propylene glycol acetates to propylene oxide (PO) is carried out in a laboratory-scale fixed-bed reactor. Potassium salts (0.5–2.5 mmol K/g) on silica are identified as selective catalysts for the reaction. A temperature of 400 °C at high space velocity gives a maximum PO selectivity of 81%, while the maximum yield of 30% is achieved at the same temperature but lower space velocity. Pre- and post-reaction catalysts were characterized by N 2 adsorption, TGA, XPS, and FTIR. High temperature and high potassium loading lead to collapse of the silica pore structure, and in severe cases to obstruction of flow in the reactor. Potassium carbonate, formed via ketonization of potassium acetate generated on the support during reaction with KOH as the catalyst material, is the stable potassium species on the catalyst at high loadings (>1.5 mmol K/g silica). At low loadings, surface potassium silicate analogs (Si-O-K) predominate. The use of potassium on a low surface area, annealed silica support gives similar activity and PO selectivity without degradation of pore structure. [ABSTRACT FROM AUTHOR]

A multilinker non-interpenetrated metal-organic framework, UMCM-15, was synthesized by using microwave power as an alternative energy-efficient tool for the first time. The synergistic catalytic activity, when combined with a co-catalyst containing a strongly nucleophilic anion, was studied in the solventless room temperature cycloaddition between epoxides and CO 2 . Unlike previous reports on UMCM-15 synthesized in the high-boiling solvent dimethylformamide, low boiling water/ethanol mixture was used as the solvent herein. This approach holds potential as a sustainable green methodology. Crystal formation during the microwave-assisted (MW) synthesis was monitored at certain time intervals. The favorable role of non-interpenetrated pillared structures in promoting room temperature CO 2 -epoxide cycloaddition reactions was explained by comparing the catalytic efficiency of the three-linker extended pillar-layered non-interpenetrated UMCM-15 with its analogous pillared structures built from two- and three-fold interpenetrated ([Zn 2 (BDC) 2 (4,4′-bipy)] and [Zn 2 (NDC) 2 (4,4′-bipy)]) catalytic systems with a single dicarboxylate linker. The efficacy of the microwave-assisted UMCM-15(M) catalyst in cycloaddition reactions was proved by comparing the catalytic activity of UMCM-15(M) with that of the congener made by solvothermal synthesis, UMCM-15(S). In addition, a plausible mechanism for the synergistic operation of the Lewis acid sites and nucleophiles was suggested. [ABSTRACT FROM AUTHOR]

The synthesis of 1-methoxy-2-propanol (1-MP), which is expected as a safe alternative for toxic ethylene glycol ether, is highly demanded in chemical engineering. Herein, we report a series of task-specific anion-functionalized poly(ionic liquid)s (PILs) to trigger an effective catalysis in the 1-MP production through a reaction of propylene oxide (PO) and methanol. The acquired PIL catalysts, which are induced by phenolate anions, allow extraordinary PO conversion of 90.8 % and outstanding 1-MP yield and selectivity of 86.5 % and 95.3 % under very mild conditions. It also feasibly applies to the catalysis of a wide range of alcohols and PO to synthesize propylene glycol ethers (PGEs), and shows robust and facilitate reusability. Through a DFT calculation and in-situ 2D-IR survey, we reason that these significant performances are enabled by hydrogen-bonding interaction from the imidazole on the backbone for PO activation, and by the unique nucleophilicity of anions for the generation of activated methanol. [Display omitted] • P[BVim]PhO enables production of propylene glycol monomethyl ether under mild conditions. • P[BVim]PhO shows robust and facilitate reusability. • DFT calculation and in-situ 2D-IR survey confirm the catalytic mechanism. • Our PILs activate methanol and propylene oxide by nucleophilic anions and imidazole groups. [ABSTRACT FROM AUTHOR]

A series of Ag-based catalysts were studied for direct epoxidation of propylene using molecular O 2 as the oxidant. Ag supported on CaCO 3 and α-Al 2 O 3 were prepared as base materials to study. Different amounts of alkali earth metal promoter (K) and feed additives, ethyl chloride (EtCl) and nitric oxide (NO), were added to the catalyst and feed stream, respectively, to evaluate their effects on catalyst performance in terms of PO selectivity and propylene conversion. A conventional catalyst supported on α-Al 2 O 3 performed similarly to the ARCO Ag (50 wt%) catalyst, supported on CaCO 3 , at a much lower Ag loading (12 wt%). EtCl inhibited consecutive oxidation presumably by Cl deposition on Ag sites and NO increased activity possibly by Ag-catalyzed oxidation of NO to NO x which was the selective oxidant. K+ promoter loadings as high as 1.9 wt% were essential to stabilize both Cl and NO x on the catalyst surface. PO Selectivities as high as 50 % were obtained. [Display omitted] • CaCO 3 has no properties making it superior to conventional α-Al 2 O 3. • High levels of ethyl chloride required to lower combustion rates of gas phase propylene oxide (PO). • High levels of K+ promotion required to maintain selectivity to PO, possibly by stabilizing Cl on Ag surface to prevent bulk AgCl formation. • Nitric oxide (200 ppmv) in feed required to improve catalytic activity, likely due to Ag-catalyzed oxidation of NO to NO 2 /NO 3 as active oxidants for PO formation. • Selectivity to PO improved from 6 % to 50 % for catalyst with optimal promoters and gas phase additives. [ABSTRACT FROM AUTHOR]

Here, we study the direct synthesis of propylene oxide (PO) on Pd-based catalysts operating under mild conditions (40 °C, 5.5 bar) and in a continuous flow microreactor. We show that the PO yield can be improved by a factor of two, with respect to the values present in literature, by using a Pd–Pt/TS-1 catalyst in excess of oxygen. Moreover, we compare the PO reaction with the hydrogen peroxide (H 2 O 2 ) synthesis, being H 2 O 2 (or OOH species) the intermediate and rate limiting step of the direct PO formation. We found that the optimal conditions for the PO synthesis are not advantageous for the H 2 O 2 productivity. In this respect, the presence of Pt, which improves the PO selectivity by lowering the hydrogenation of propylene, negatively affects the H 2 O 2 productivity due to an acceleration of its side reactions. This effect is more pronounced for the Pd–Au/TS-1 catalyst, which shows a high performance for H 2 O 2 production. However, the PO formation remains relatively poor due to a very fast hydrogenation of propylene to propane. We conclude that the optimization of the H 2 O 2 synthesis is not sufficient to improve the direct PO formation. Indeed, the hydrogenation of propylene needs also to be considered. [ABSTRACT FROM AUTHOR]

Different bi-functional materials (Pd(Au)@TS-1) based on metallic nanoparticles supported onto active nanocrystalline titanium silicalite (TS-1) zeolites were synthesized, characterized and used as recyclable heterogeneous catalysts for direct propylene oxide production from hydrogen, oxygen and propylene through one-pot two-step consecutive process. These catalysts allowed carrying out the combined reaction where metallic nanoparticles catalyzed the formation of in situ H 2 O 2 that was the necessary intermediate for propylene epoxidation catalyzed by active TS-1 nanocrystalline support. Several variables were considered such as use of supercritical CO 2 conditions, modifiable content of metallic species, and presence of additional co-solvents, surface acidity inhibitors and H 2 O 2 stabilizers. Reusability and stability of the bi-functional catalyst was showed through consecutive catalytic cycles. [ABSTRACT FROM AUTHOR]

A TS-1 catalyst layer has been coated inside a capillary microreactor by the transformation of a porous silica precoating using an in-situ hydrothermal synthesis method. The use of the silica precoating to favour TS-1 nucleation and growth on the microchannel surface has shown to provide a final TS-1 coating of high surface area and titanium loading with good stability. The ability to transform the silica precoating to a TS-1 coating was achieved by correctly balancing the silica precoating dissolution, zeolite nucleation and growth rates, and insertion of titanium into the zeolite framework. The 4 μm TS-1 coating, consisting of TS-1 crystals of approximately 800 nm in size, was applied in the epoxidation of propene as a model reaction to demonstrate its catalytic activity. The TS-1 microreactor obtained a propylene oxide productivity of 2 g PO /g cat h with a propylene oxide selectivity above 90%. Long-term stability tests of the TS-1 microreactor showed that the TS-1 coating is very stable with only a small deactivation noted over a 500 h time-on-stream period. [ABSTRACT FROM AUTHOR]

A single-component synergistic catalytic system, in which multiple active sites act on a substrate with minimal energy input and promote efficient conversion of the substrate, is considered to be the most advanced technology for simulating enzyme catalytic reaction. The design principles of this technology are the driving force behind the pursuit of cost-effectiveness in industrial production, but the challenges remain formidable. Herein, three periodic mesoporous polyamides with triazine-derived networks (PMP-TDNs) were prepared via "one-pot" polycondensation, and used as non-metallic catalysts for cycloaddition of CO 2 with epoxides without any additives to synthesis cyclic carbonates. The composition and physicochemical properties of PMP-TDNs were evaluated via different analytical methods to explore the crucial factors affecting catalytic activity. Especially, the activity of PMP-TDNs-MI with multiple hydrogen bond donor (HBD) and high-density N basic sites have been tested effectually; the results has demonstrated a superior reactivity for the cycloaddition of CO 2 and a wide range of epoxides with reusability. The kinetics and thermodynamics of cycloaddition of CO 2 with propylene epoxide by PMP-TDN S -MI were investigated, and the cooperative catalytic mechanism between the versatile active sites of catalyst was revealed based on the experimental results. [Display omitted] • Three PMP-TDNs were presented and their activities for CO 2 cycloaddition were investigated. • PMP-TDNs-MI showed superior activity for the cycloaddition of CO 2 with epoxides (yield ~99.9%), without additives and with reusability. • The cooperative mechanism between the versatile active sites of PMP-TDNs-MI was revealed based on the experiments. • The kinetics and thermodynamics of PO/CO 2 cycloaddition catalyzed by PMP-TDN S -MI were studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] Propylene undergoes gas-phase selective epoxidation with CO/O2 reactants over Au/TiO2. [•] The reaction is analogous to the known epoxidation of propylene with H2/O2 mixture. [•] Either CO and H2 are the necessary reducing co-reagents to perform the reaction. [•] CO and H2 induce a formation of the same active oxygen species. [ABSTRACT FROM AUTHOR]

Abstract: Tetramethylguanidine covalently bonded to silica was found to be an efficient and recyclable catalyst for the synthesis of propylene carbonate (PC) from propylene oxide (PO) and carbon dioxide. The catalyst was prepared, first by the coupling of 3-(chloropropyl)triethoxy silane with silica from rice husk ash (RHA), to form 3-chloropropyl silica (RHACCl). This was later grafted with tetramethylguanidine molecule to form a solid base catalyst (RHAPrTMG). The surface morphology analyzed by TEM, revealed the presence of spherical nanoparticles with an average size of 19.62nm. The 13C solid state NMR indicated the presence of 5 sets of carbon atoms in the structure. A conversion of 92% was achieved under the optimized reaction conditions (130°C, 5.0MPa, 8h), with a propylene carbonate selectivity of ca. 98%. The catalyst can be easily recovered by filtration and reused for at least four times without appreciable loss of its catalytic activity. [Copyright &y& Elsevier]

Abstract: Al2O3/MgO materials with various Mg/Al molar ratios were prepared and characterized by XRD, FT-IR, SEM and BET analysis. These materials were used as catalysts for synthesis of 1-phenoxy-2-propanol (1-PhP) from phenol and propylene oxide as compared with some oxides, i.e. MgO, CaO, ZnO and Al2O3, etc. Al2O3/MgO with Al/Mg molar ratio of 1.5% exhibited outstanding catalytic performance with 98.2% conversion and 99.3% selectivity to 1-PhP at 120°C for 5h. This catalyst can be easily recovered and reused due to its heterogeneous catalytic nature. [Copyright &y& Elsevier]

Abstract: The gas-phase epoxidation of propylene using nitrous oxide as an oxidant over nanostructured iron-containing catalysts was studied. Various types of catalytic systems were used, and the effort was aimed at obtaining propylene oxide as the main product of the reaction. Catalysts prepared on various supports with different porosities, various amounts and types of promoters have been tested. The function of potassium chloride and other promoters was investigated with the aim to understand their effect of the iron incorporation into the silica matrix. It has been found that after a partial removal of KCl from the iron-containing catalyst, a maximum of 54% propylene conversion can be obtained. In the presence of calcium promoter, 96% selectivity of propylene oxide formation was reached at 21% conversion of propylene. [Copyright &y& Elsevier]

Abstract: The fluorine-modified Mg–Al mixed oxides were synthesized by thermal decomposition of the fluorine-containing Mg–Al hydrotalcites, and their physicochemical properties were characterized by ICP, TGA, XRD, FTIR, CO2-TPD and N2 adsorption/desorption techniques. It was found that weak basic sites were gradually transformed into moderate and strong basic sites during thermal decomposition, and thus weak basic sites (OH− groups), moderate basic sites (Mg–O, Mg–F and Al–O pairs) and strong basic sites (coordinatively unsaturated F− and O2− ions) were all produced in the as-prepared samples. Furthermore, the basicity of moderate basic sites could be controlled by the change of fluorine content, which caused the change in the amounts of Mg–F pairs. In the synthesis of propylene glycol methyl ether from methanol and propylene oxide, the base-catalytic performance of the obtained samples was shown to be closely associated with their moderate basic sites. [Copyright &y& Elsevier]

Abstract: The catalytic transfer hydrogenolysis (CTH) of α-methylbenzyl alcohol (MBA) was studied using palladium catalysts and formic acid, with the intent of developing a new approach for the production of propylene oxide (PO). The effects of support, hydrogen donor, molar ratio of HCOOH to MBA, water content, reaction temperature and catalyst recycling were evaluated. Using formic acid as hydrogen donor and Pd/C as catalyst, one can convert MBA to ethylbenzene (EB) with very high selectivity (98.8%) and high conversion (98.8%) at 80°C for 40min. H+ ion plays an important role, for it promotes the formation of active hydrogen species in the reaction process. A reaction mechanism was proposed to account for the results obtained in the study. [Copyright &y& Elsevier]

Abstract: The gas-phase epoxidation of propylene using nitrous oxide as an oxidant over bulk and supported iron-containing catalysts was studied. The presence of silica and an alkaline metal in both types of catalysts was found to be indispensable. Bulk catalysts formed in potassium–iron mixed silicates were studied, with respect to their crystalline structure, oxidation state and performance in propylene epoxidation. Over these catalysts a 69% selectivity to propylene oxide at 1.6% propylene conversion was reached. The presence of separated iron oxide phase was shown to promote the undesired allylic oxidation of propylene. Supported, halide-modified Fe-containing catalysts exhibit a superposition of two epoxidation routes. One, independent of air-pretreatment, shows similarity with that observed at bulky potassium–iron silicates; and the second, more selective, induced by air-pretreatment. The second mechanism, dominant in the first 30min on stream, results in a maximum of 45.7% propylene conversion at 70% selectivity to propylene oxide. An improvement of the epoxidation activity was obtained, comprising reaction–reactivation switching steps. A reaction mechanism involving KCl as an oxygen transmitter and a metastable form of iron moieties is suggested. [Copyright &y& Elsevier]

Several double metal cyanide (DMC) catalysts based on Zn3[Co(CN)6]2 were prepared by an impregnation method. Infrared spectroscopy (IR), wide-angle X-ray diffraction (WAXD), and elemental analysis were used to characterize these DMC catalysts. The WAXD patterns showed that pure Zn3[Co(CN)6]2 had very high crystallinity (98.8%) with a typical cubic lattice structure, while DMC catalysts prepared with excess ZnCl2 and/or complexing agents had low crystallinity. Furthermore, no free ZnCl2 was found in DMC catalysts prepared with excess ZnCl2 (from WAXD characterization), although it seemed that free ZnCl2 existed in the catalyst (from elemental analysis). The characteristic absorptions (νCN and νCo–C) in the IR spectra of DMC catalysts prepared with excess ZnCl2 were shifted to higher wave numbers than those in pure Zn3[Co(CN)6]2. These results showed that a new chemical linkage was produced between Co(CN)63− and ZnCl2 (or zinc center complexes) in the precipitation reaction. Excess ZnCl2 in DMC catalyst preparation was necessary to ensure its high catalytic activity for ring-opening polymerization (ROP) of propylene oxide (PO), while complexing agents were unnecessary in the composition. The role of the complexing agents was mainly to promote the formation of the amorphous DMC catalyst and thus increase the catalytic activity. A possible heterogeneous coordinative cationic polymerization mechanism is proposed for a reasonable interpretation of the ROP of PO. [Copyright &y& Elsevier]

Abstract: The vapour phase epoxidation of propene with nitrous oxide (N2O) was experimentally investigated in a fixed bed reactor using a CsO x /FeO y /SiO2 catalyst in a broad range of residence times. A complex reaction network was derived from the trends of product selectivities as function of the conversion. For the determination of the reaction paths, not only propene but also its oxidation products, propylene oxide (PO) and propionaldehyde (PA), were used as reactants. The selectivity to PO was found to be limited due to fast side reactions, like PO isomerisation reactions and, in particular, the formation of higher molecular weight products (HMP) mainly present as carbonaceous deposits (coke) on the catalyst. The amount of HMP and coke was quantified through several methods and both were identified as the major byproducts. Although PO is formed with more than 60% selectivity among the directly identified vapour phase products, the maximum selectivity is only about 30% when taking the HMP into account. [Copyright &y& Elsevier]

Abstract: It was found that silica-supported molybdenum oxide was high effective for the epoxidation of propylene among various silica-supported metal oxides. The post-catalytic bed volume played an important role in its formation. On a MoO x /SiO2 with 0.255mmol/g-SiO2, a propylene conversion of 17.6% and a PO selectivity of 43.6% were obtained at 5atm, 573K and flow rates of C3H6/O2/He=10/5/10cm3 min−1. The characterization studies indicated that crystalline MoO3 nano-particle species was more effective for propylene epoxidation to PO than molecularly dispersed Mo oxide species. The reaction mechanism of propylene epoxidation on MoO x /SiO2 catalysts is hypothesized to involve gas-phase radicals generated at relatively low temperature by the dispersed molybdenum oxide species. These radicals participated in homogeneous reactions with molecular oxygen to produce propylene oxide. [Copyright &y& Elsevier]

Abstract: A covalently immobilized zinc pyridine bromide complex was investigated in the solvent-less synthesis of propylene carbonate (PC) by fixation of carbon dioxide (CO2) in propylene oxide (PO). The reaction was optimized using phase behavior studies based on video monitoring, transmission and attenuated total reflection (ATR) infrared measurements. At first the immobilization process was monitored by DRIFTS which confirmed the successful fixation of the ZnBr2(Py)2-complex on the silica matrix. Phase behavior studies of the reaction mixture showed three different regions that influenced strongly the reaction rate: (i) At low overall density a biphasic region with small liquid phase (high molar ratio of PC) was observed. The catalytic activity of this system was poor. (ii) A decreasing CO2 content at the same density resulted in an expanded liquid phase, which was up to a certain PO/PC ratio beneficial for the catalytic activity. However, at too low content of CO2 (ratio CO2/(PO+PC)<4) the rate decreased again, because CO2 is not only solvent but also reactant in the synthesis of PC. (iii) Finally, experiments at higher pressure led to a single-phase system (“supercritical conditions”). Despite of optimal mass transfer properties the lowest conversion was achieved under these reaction conditions. These observations provided important insight into the reaction system. In situ ATR-IR studies of the catalyst surface during reaction revealed drastic changes in the phase behavior in the first minutes and gave important insight into the solid/fluid interface under reaction conditions. [Copyright &y& Elsevier]

Abstract: In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al2O3 and CaCO3 were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO3 catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56wt.% supported on CaCO3 and promoted with 1wt.% NaCl (Ag(56)–NaCl(1)/CaCO3). The catalysts were tested with reactant flow rates of C3H6:O2:He=5:10:15cm3 min−1, a gas hourly space velocity (GHSV) of 1800h−1, a reaction pressure of 0.3MPa, and a reaction temperature of 533K (260°C). Addition of 500ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO3 catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO3 catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag+ species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO3 support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag+ species on the surface of the Ag(56)–NaCl(1)/CaCO3 catalyst could be the cause of a decline in PO selectivity observed during reaction. [Copyright &y& Elsevier]

Abstract: Ti/SiO2 epoxidation catalysts with titanium concentration ≤1.12μmol/m2 were prepared by chemical deposition of TiCl4 vapor on silica gel at 900°C for 0.5–3h. A zero-order rate law was able to satisfactorily describe the deposition process in the range of Ti ≤1μmol/m2. The CVD-prepared Ti/SiO2 catalysts were used to catalyze the epoxidation of propylene and 1-octene to the corresponding epoxides (propylene oxide and 1,2-epoxyoctane) with cumene hydroperoxide (CHP) and tert-butyl hydroperoxide (TBHP) as the oxidants. The epoxide selectivity increased rapidly with Ti concentration. For the catalyst containing the maximum Ti concentration, the epoxide selectivities were insensitive to the oxidant type, and had 97% 1,2-epoxyoctane yield and 93% propylene oxide yield. For the catalysts containing the lower Ti concentration (i.e., with residual SiOH groups), CHP exhibited significant higher epoxide selectivity than TBHP. The results suggest that the oxidant type had a stronger effect on the hydroperoxide decomposition rate (that occurred on the Si–O–H Bronsted acid site) than on the epoxidation rate (that occurred on the Si–O–Ti site), and that CHP had a significantly lower decomposition rate than TBHP. This is opposite to the results reported before for the hydroperoxide stability in the presence of liquid acid. When CHP was used as the oxidant, the rate of propylene epoxidation was found to be first-order with respect to the CHP concentration; the kinetic parameters were determined. [Copyright &y& Elsevier]

Abstract: A series of Au/TS-1 catalysts with varying gold and titanium contents was prepared by deposition–precipitation (DP) and examined at 140–200°C in a 10/10/10/70 vol.% mixture of hydrogen, oxygen, propylene and helium at a space velocity of 7000mL/h/gcat. Gold loading was found to be closely related to titanium loading, implying that low gold loadings using deposition–precipitation results in an inherently small number of very active sites. Forcing the gold loading to higher values resulted in poor activity and stability. A catalyst prepared with a Si/Ti=36 and a gold loading of 0.05wt% produced 116gPO/h/kgcat at 200°C, which is the highest rate thus reported for a TS-1-based catalyst, with no evidence of deactivation during the 40h temperature program. Catalysts prepared with lower titanium and gold contents resulted in very active catalysts when rates were normalized to the total gold content, 350gPO/h/gAu at 200°C for 0.01wt% Au/TS-1 (Si/Ti=500), indicative of the more efficient use of gold and titanium for the epoxidation reaction. The low gold loadings coupled with the absence of gold particles in TEM micrographs make it likely that, in these materials, significant activity is attributable to gold entities much smaller than 2nm. [Copyright &y& Elsevier]

Abstract: The synthesis of dimethyl carbonate (DMC) from methanol, propylene oxide (PO) and carbon dioxide (CO2) over supported catalysts was studied for the first time. A series of supported solid base catalysts were prepared by impregnation and their catalytic activities were evaluated. It was found that KOH/4A molecular sieve was the most effective catalyst. The effects of various conditions, such as reaction time, reaction temperature, molar ratio of the reactants and KOH loading, on the yield of DMC was investigated. It was proposed that DMC was formed from the transesterification of propylene carbonate (PC) with methanol, where PC was synthesized from PO and carbon dioxide. Methanol was favorable to such cycloaddition of PO with CO2. Under the optimized conditions, PO was converted completely and the yield of DMC was up to 16.8%. [Copyright &y& Elsevier]

A zinc-substituted sandwich-type polyoxometalate, Na12[WZn3(H2O)2(ZnW9O34)2]·46H2O, in conjunction with a Lewis base was found to be efficient for the cycloaddition of CO2 with epoxides to form cyclic carbonates. The catalyst system was tested for a few representative epoxides, including epichlorohydrin, propylene oxide and butylene oxide; the reactions were carried out at moderate CO2 pressure (0.4–1.0MPa) in the temperature range 100–160°C. Using the present catalyst system, one could obtain near-quantitative conversion and high selectivity with or without organic solvents. The zinc-substituted polyoxometalate part of the catalyst system is heterogeneous, easy to separate after completion of reactions and reusable for many runs. [Copyright &y& Elsevier]

One of problems connected with the use of gold/titania-based catalyst systems is the low yield in propene oxide (up to 2 wt.%). It is shown that the low propene oxide yield is due to product inhibition. New catalysts and process options for propene epoxidation with hydrogen and oxygen are discussed. [Copyright &y& Elsevier]

The effects of preparation conditions, treatment methods of the Ag/TS-1 catalyst and the reaction conditions on propylene epoxidation using oxygen as the oxidant in a fixed-bed quartz reactor were investigated. The catalysts were characterized by XRD, UV-Vis, TEM and ESR spectra. Results show that hydrogen is essential for the epoxidation reaction. The optimum preparation conditions are as follows: Ag loading 2 wt.%, the ratio of Si/Ti in TS-1 64, and calcination temperature (in air) 450 °C. The optimum Ag/TS-1 catalyst, by passing a reactant mixture of C3H6, O2, H2 and N2 at 150 °C at a volume ratio of 1:2:3:12 with a space velocity of 4000 h−1, can exhibit the best results. At this condition, after 70 min reaction the conversion of propylene and the selectivity to propylene oxide are 1.37 and 93.51%, respectively. The results of the characterization show that the oxidized Ag species without single electrons plays an important role in the epoxidation of propylene. [Copyright &y& Elsevier]

Double metal cyanide (DMC) complexes based on Zn3[Co(CN)6]2 were prepared using different zinc salts and complexing agents and They were characterized by elemental analysis, IR and XRD. The catalytic properties of DMC complexes were determined in polymerization of propylene oxide. Great differences in morphology of DMC complexes was were correlated with preparation route as well as with the kind of zinc salts employed. The catalytic activity was strongly dependent on the morphology of DMC complexes and composition of catalysts. The study revealed that the amorphous catalyst made from ZnCl2 and t-BuOH had the highest activity (up to 26 kg polymer/g catalyst). The DMC catalyst was non-stoichiometric. Polymerization of propylene oxide (PO) catalyzed by DMC proceeded in a controlled manner. The molecular weight of each polymer was controlled by the monomer/initiator ratio, the values of molecular weight distribution (MWD) were in the range of 1.23–1.48. The polymer has an atactic structure and a head-to-tail regiosequance. [Copyright &y& Elsevier]

Ti-containing MCM-41 supports were prepared by: (a) hydrothermal crystallization; (b) post-synthesis grafting; and (c) two-step Ti incorporation—hydrothermal incorporation followed by post-synthesis grafting. XRD revealed little change in crystallinity and long range order of MCM-41 phase after Ti incorporation by different methods. UV-Vis spectra show the presence of tetrahedral Ti sites at lower Ti contents (upto 4.5 mol%), but aggregated titania formation could be observed at higher Ti loadings (>4.5 mol%). The samples exhibit surface areas and pore volumes in the mesoporous range. Vapor phase epoxidation of propene using H2 and O2 was carried out over these supports after Au deposition by deposition-precipitation (DP) method. The Ti-MCM-41 supports prepared by two-step Ti incorporation (with up to 4.5 mol% input Ti), which probably have more number of isolated Ti sites, showed higher catalytic activity than Ti-MCM-41 prepared by one-step Ti incorporation method, at comparable propylene oxide selectivities and hydrogen efficiencies. The former catalyst also deactivates more slowly than the latter ones, probably due to a decrease in the number of silanol sites (those responsible for deactivation) due to grafted Ti. [Copyright &y& Elsevier]

Hydrogenolysis of α-methylbenzyl alcohol (MBA), a co-product of propylene oxide (PO) in hydrocarbon peroxide oxidation processes, was studied to develop a by-product-free PO process. The conversion of MBA was mainly affected by the acidity of the support. Among the metals tested, Pd was most active and selective for the formation of ethylbenzene (EB). The hydrogenation of MBA exhibited type II selectivity, meaning that the selectivity to main products is controlled by reaction conditions and metals chosen. On Pd or Ni, the formation of EB is predominant while on Ru or Pt, that of 1-cyclohexylethanol (CHE) prevails. By carefully designing the catalyst and selecting the reaction condition, one could obtain a very high yield of EB with only a small amount of side products. Based on the results, a bifunctional reaction mechanism was proposed. [Copyright &y& Elsevier]

The propylene epoxidation using supported titanium silicalite TS-1 catalyst was systematically investigated in a fixed bed reactor. Different supports such as SiO2 and Al2O3 were used and two molding methods were adopted to prepare the catalyst. Strip TS-1 catalyst of 1 mm×2 mm dimensions is obtained by the extruding method. Use of SiO2 as the support rather than Al2O3 is better because the latter has strong acidity that promotes the side reaction of propylene oxide (PO) with the solvent. With the decrease of the amount of TS-1 in TS-1/SiO2, the PO selectivity increases. The lamina TS-1 catalyst, the core of which is an inert ball used as the support and the shell of which is a TS-1 lamina of 0.1–0.2 mm, exhibits better performance than the strip TS-1 catalyst owing to its shorter diffusion path for reaction heat, raw material and product. The lamina TS-1 catalyst was used in the fixed bed reactor for about 200 h. The results indicate that it is a promising catalyst in propylene epoxidation. The effect of aluminum impurity was also investigated. It has been shown acid sites originating from framework aluminum can catalyze the side reaction and a small amount of base can inhibit it. In conclusion, diffusion and the concentration of acid sites are the two main factors influencing the performance of titanium silicalite catalyst in propylene epoxidation. [Copyright &y& Elsevier]

[Display omitted] • MIL-101-N(Bnme 2)Br catalyst was prepared by coupling MIL-101-NH 2 with the ionic liquid (N(BzBnme 2)Br). • The MIL-101-N(Bnme 2)Br has high activity for the cycloaddition reaction of CO 2 and epoxides. • MIL-101-N(Bnme 2)Br could be recycled easily by filtration with good reusability. The reaction of CO 2 with epoxides to produce cyclic carbonates requires high-performance, low-cost, and facilely recycled catalysts. Here, we report a heterogeneous catalyst (MIL-101-N(Bnme 2)Br) based on metal-organic frameworks (MOFs) for catalytic CO 2 conversion into cyclic carbonates. The MIL-101-N(Bnme 2)Br catalyst was prepared as follows: A MOFs precursor (MIL-101-NH 2) was firstly synthesized using a method of hydrothermal synthesis, then coupled with the quaternary ammonium salt ionic liquid (N(BzBnme 2)Br) via aldehyde-amide condensation. A series of comparative experiments revealed that MIL-101-N(Bnme 2)Br catalyst has high activity for catalyzing the cycloaddition reaction to produce cyclic carbonates in the absence of solvents and co-catalysts. As was exampled by the synthesis of propylene carbonate, a high yield (93 %) and selectivity (99 %) was achieved under the optimized conditions (0.93 mol% MIL-101-N(Bnme 2)Br catalyst, 1.4 MPa CO 2 pressure, 17 mmol propylene oxide, 100 °C, 5 h). More impressive, the MIL-101-N(Bnme 2)Br catalyst could be recycled easily by filtration and was reusable up to several times without a significant activity decay. Furthermore, our density functional theory (DFT) calculations suggested that such high catalytic activity mainly resulted from the cooperative catalysis between the coordinatively unsaturated Cr3+ sites and Br anions in MIL-101-N(Bnme 2)Br catalyst. Meanwhile, a possible mechanism for the cycloaddition reaction catalyzed by MIL-101-N(Bnme 2)Br catalyst was also proposed. [ABSTRACT FROM AUTHOR]

Zn and Na+ species could synergistically promote the reduction of Cu2+ to Cu+ species. Cu+ species played a vital role in PO formation and Cu+ species may be the main active site for C 3 H 6 epoxidation reaction by O 2. [Display omitted] • Appropriate amounts of Zn species and Na+ were both beneficial to the PO formation. • The increase of PO selectivity was mainly due to Na+ instead of Cl−. • Zn and Na+ species synergistically promoted the transformation of Cu2+ to Cu+ species. • Cu+ species may be the active site and be responsible for C 3 H 6 epoxidation by O 2. The catalytic performances of Cu-Zn/SiO 2 with different Zn content and promoter on C 3 H 6 epoxidation were investigated. Zn species was in favour of the formation of propylene oxide (PO), and PO selectivity was further increased after Cu-Zn/SiO 2 was modified by Na+. The promotive effect of Na+ on C 3 H 6 epoxidation activity was much superior to that of Cl−. The PO formation rate on Cu 92 Zn 8 /SiO 2 -Na 2 CO 3 was nearly as high as 50 times that on Cu/SiO 2. Zn and Na+ could synergistically promote the reduction of Cu2+ to Cu+ species. The variation tendencies between C 3 H 6 epoxidation activity and Cu+ content were in good agreement with each other. The role of Zn and Na+ was to enhance the Cu+ content via promoting the reduction of Cu2+ to Cu+ induced by Zn and Na+. Cu+ species played a vital role in PO formation and Cu+ may be the active site for C 3 H 6 epoxidation reaction by O 2. [ABSTRACT FROM AUTHOR]