Search

At present, there is no low pressure methanol synthesis from CO2/H2 with high yield despite the presence of an upstream process of aqueous phase reforming (APR) of biomass derivatives on an industrial scale for CO2/H2 production at ca. 2 MPa. This is due to the intrinsic thermodynamics of the system which leads to particularly high CO levels at low pressure through reversed water gas shift reaction (RWGS) for most studied catalysts. Here we report a new Pd@Zn core–shell catalyst that offers a significantly higher kinetic barrier to CO/H2O formation in CO2 hydrogenation to reduce the CO levels but facilitates CH3OH formation at or below 2 MPa with CH3OH selectivity maintained at ca. 70% compared to ca. 10% over industrial Cu catalysts. The corresponding methanol yield at 2 MPa reaches 6.1 gmethanol gactive metal−1 h−1, which is comparable to the best reported value among a wide variety of catalysts under 5 MPa. It is thus believed that this active Pd based catalyst opens up a promising possibility for low pressure and temperature methanol production using a renewable biomass resource for fossil-fuel-starved countries. [ABSTRACT FROM AUTHOR]

The conversion of methanol to aromatics such as benzene, toluene, and xylenes (BTX) was performed over HZSM-5-supported bimetallic Zn-Sn catalysts. The results indicated that Sn species preferentially healed the defects in HZ crystals to create new active sites. The catalyst with Zn species markedly enhanced the aromatization performance but easily produced heavy coke. Thus, an optimized catalyst with 1 wt% Zn and 1 wt% Sn exhibited improved catalytic performance in terms of selectivity and BTX yield compared with a catalyst with a single metal. Consequently, the BTX yield was 64.1 % under the reaction conditions of 0.1 MPa and 0.8 h methanol weight hourly space velocity at 450 °C. Graphical Abstract: The HZSM-5 supported bimetallic catalyst 1 % Zn-1 % Sn/HZ exhibits a higher BTX yield than 2 % Sn/HZ and a longer lifetime than 2 % Zn/HZ. The deactivated catalyst can be regenerated for several times without significant reduction in catalytic performance. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Amino-functionalized MCM-41 and MCM-48 mesoporous silicas were used to immobilize CuCl2 for the vapor-phase oxy-carbonylation of methanol to produce DMC. Higher reaction rates and better catalytic stability were obtained with CuCl2 supported onto amino-functionalized MCM-41 and MCM-48 in the DMC yield in comparison with those with CuCl2 supported on nonfunctionalized mesoporous silicas under identical conditions. The best DMC yield was obtained with a CuCl2 loading of about 10 wt%, which corresponds to the N/Cu atomic ratios of 1.5 and 2.4 in the CuCl2/1N-MCM-41 and CuCl2/2N-MCM-41, respectively. Characterizations with XRD, N2 adsorption, XPS, and HRTEM revealed that the regular hexagonal/cubic arrays in MCM-41 and MCM-48 were retained after the amino-functionalization and the immobilization of CuCl2 with a loading weight lower than 20 wt%. The Cu species in the catalysts with loadings lower than 10 wt% were mainly located and finely dispersed in the mesopores of amino-functionalized MCM-41 and MCM-48 through a coordinative complexation with the amino groups, forming (N)2 → Cu2+ complex species. The better performance of CuCl2 on amino-functionalized MCM-41 and MCM-48 for the DMC production via vapor-phase oxy-carbonylation of methanol may be ascribed to the high dispersion of active sites at regular mesopores, in addition to the accelerated redox process of Cu2+/Cu+ in the complex species. [Copyright &y& Elsevier]

Pure silica mesoporous molecular sieves MCM-41 and MCM-48 organofunctionalized with 3-aminopropyltrimethoxysilane and N-[(3-trimethoxysilyl)propyl]ethylene-diamine, respectively, were served as supports to immobilize CuCl2 with conventional impregnation method. The supported copper catalysts showed a considerable enhancement in the reaction rate in heterogeneous vapor-phase oxidative carbonylation of methanol to produce dimethyl carbonate in comparison with that obtained by CuCl2-supported nonfunctionalized mesoporous silicas under identical conditions. The electronic donation of the amino groups, the accessibility and dischargeability of reactants in the regular mesopores probably account for the good catalytic performance as evidenced by the characteristic studies with XRD, BET, FTIR, TG-DTA, and XPS. [ABSTRACT FROM AUTHOR]

Three crystalline compounds, SbOReO4·2H2O, Sb4Re2O13 and SbRe2O6, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH3OH+½O2 → CH2(OCH3)2+2H2O). A high selectivity of 92.5% to methylal at a conversion of 6.5% under conditions of GHSV = 10000 mL h-1g-1-cat and 573 K was obtained on the new SbRe2O6 catalyst, while no significant formation of methylal was observed with the other two catalysts. No structural change in the bulk and surface of SbRe2O6 and Sb4Re2O13 occurred after methanol oxidation below 593 K, but SbOReO4·2H2O was transformed to Sb4Re2O13, as characterized by XRD, Raman spectroscopy, XPS and SEM. The high performance of SbRe2O6 for the selective methylal synthesis was ascribed to Re oxide species stabilized by a specific connection with Sb oxides at the crystal surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • NaCl nanocrystals were used as a template for the synthesis of few layer MoS 2. • Sodium is able to promote the formation of in-plane sulfur defects. • The catalyst evolution throughout the induction period was studied in detail. • Sodium-assisted sulfur vacancies lower the energy barrier of the carboxylate route. The effective conversion of CO 2 to methanol utilizing green hydrogen under moderate conditions represents a promising approach for achieving carbon neutrality. MoS 2 demonstrates exceptional catalytic performance at temperatures below 200 °C, however, generating in-plane sulfur defects is challenging due to the intact planar structure. Introducing heteroatoms to induce sulfur vacancy formation and modulate their chemical environment remains a significant obstacle. In this study, we developed a NaCl-assisted method for synthesizing MoS 2 and discovered that a small quantity of sodium not only promotes the formation of sulfur vacancies during the induction period, but also encourages CO 2 hydrogenation via the carboxylate route, as opposed to the CO 2 dissociation to CO* route over non-modified sulfur vacancies. Furthermore, catalysts at various stages throughout the 60 h induction period were characterized, revealing that the increase in sulfur vacancies and enhanced H 2 dissociation capability are primary factors contributing to improved methanol yield. The sodium-modified MoS 2 achieves a methanol space–time yield of up to 571 mg MeOH g cat. −1 h−1 at 200 °C and 5 MPa with a 4.8% CO 2 conversion and 96% methanol selectivity. The turnover frequency based on total sulfur vacancies reaches 170 h−1. This research is anticipated to offer a new strategy for enhancing the catalytic performance of CO 2 hydrogenation to methanol using heteroatom-assisted defect engineering. [ABSTRACT FROM AUTHOR]

N-doped carbons (NCs) have attracted considerable attention for their outstanding physicochemical properties, including tunable porosity, electronic features and modified surface. Here, we report the preparation of hierarchically porous NCs derived from the direct pyrolysis of ZIFs (ZIF-7 and ZIF-8) and poly– m –phenylenediamine-covered carbon black (P m PDA-C) for the stabilization of Cu nanoparticles (NPs). The configuration of N species can be effectively regulated by changing the ligand of ZIFs and pyrolysis atmosphere. A remarkable N configuration synergistic effect is observed in the oxy-carbonylation of methanol to dimethyl carbonate with molecular oxygen. The results indicate that the Cu NPs on pristine carbon have a turn over frequency (TOF) of 4.4 h−1 for the reaction, while those on NCs from ZIF-8 and ZIF-7 present TOF values as high as 17.9 h−1 and 28.5 h−1, respectively. The extensive characterizations reveal that NCs with a nitrogen content of 2–5 wt% and a pyrrolic-/pyridinic-N molar ratio of 2–3 are vital for the performance enhancement of Cu NPs. This work shows that the stabilization and enhanced performance of active Cu NPs on NCs are realized by the rational design of precursors to generate the proper N configurations. Image 1 • A series of NCs are prepared from ZIFs with N content in the range of 0–20 wt%. • The N configuration is regulated by ligand of ZIFs and varying pyrolysis conditions. • The performance of supported Cu catalysts is correlated with N configurations. • NCs with 2–5 wt% N and pyrrolic-/pyridinic-N ratio at 2–3 are vital for Cu catalysis. [ABSTRACT FROM AUTHOR]

• A stable Cu-based catalyst is fabricated by forming Cu–LaO x interfaces. • LaO x not only improves CO 2 adsorptionbut also enhances the dispersion of Cu NPs. • A CO 2 conversion of 6% with a selectivity of 81.2% to methanol without deterioration for 100 h is achieved. • Intermediates of methoxy and formate species are detected by in situ FTIR. • The formate route is preferable in methanol formation at Cu–LaO x interfaces. The direct hydrogenation of CO 2 to methanol has become a very active research field because CO 2 can be prospectively recycled to mitigate greenhouse effect and store clean synthetic fuels. This reaction can be catalyzed by supported Cu catalysts and the catalysts display strong support or promoter effects. Sintering of Cu species accelerates the separation of Cu–oxide interfaces, reduces the active component, and diminishes the methanol selectivity. In this work, we report a Cu catalyst supported on La-modified SBA-15, where the Cu–LaO x interface is generated through the interaction of highly dispersed Cu nanoparticles with LaO x species bedded into the SBA-15 pore wall. The optimized Cu 1 La 0.2 /SBA-15 catalyst can achieve methanol selectivity up to 81.2% with no deterioration in activity over 100 h on stream compared with the La-free catalyst. A thorough study reveals that La species not only significantly improve the CO 2 adsorption but also enhance Cu dispersion to produce well-dispersed active sites. The H/D exchange experiments show that the methanol synthesis displays a strong thermodynamic isotope effect and the Cu–LaO x interface plays a crucial role for the methanol synthesis rate in CO 2 /D 2 feed. In situ DRIFTS studies reveal that *HCOO and *OCH 3 species are the key intermediates formed during the activation of CO 2 and methanol synthesis over the Cu 1 La 0.2 /SBA-15 catalyst. [ABSTRACT FROM AUTHOR]