Qingde Zhang

A highly efficient Ga/ZSM-5 catalyst prepared by formic acid impregnation and in situ treatment for propane aromatization

A simple method for the preparation of a Ga/ZSM-5 catalyst for propane aromatization was established by formic acid impregnation and in situ treatment. The catalyst prepared by this novel method showed remarkably superior activity of propane aromatization. Under the conditions T = 540 °C, P = 100 kPa, WHSV = 6000 ml g−1·h−1 and with a N2/C3H8 molar ratio of 2, the highest propane conversion and selectivity to BTX (benzene, toluene and xylene) achieved on H–Ga/SNSA catalyst was 53.6% and 58.0%, respectively, much higher than that of the catalyst prepared using the traditional impregnation method (38.8% and 48.2%). The catalysts were characterized by nitrogen physical adsorption, ICP-AES, DRIFT, py-FTIR, NH3-TPD, H2-TPR, XPS and 27Al MAS NMR techniques. The characterization data indicated that this facile methodology enhanced the dispersion of the Ga species and promoted the formation of highly dispersed (GaO)+ species, which could exchange with the acidic protons (Bronsted acid sites) of the zeolite framework, contributing to the strong Lewis acidity. The super catalytic behavior was attributed to the synergistic effect between the strong Lewis acid sites generated by the (GaO)+ species and the Bronsted acid sites.

Selective oxidation of dimethyl ether to methyl formate over trifunctional MoO3–SnO2 catalyst under mild conditions

Dimethyl ether oxidation was conducted over MoO3–SnO2 catalysts prepared from different Sn salt precursors. Over the MoO3–SnO2 catalyst prepared from SnCl4, methyl formate selectivity reached 94.1% at 433 K without the formation of COx. The performance of the catalyst was determined by the existence form of MoO3 and the different surface bonding of Mo and O of the catalyst.

Rhenium oxide-modified H3PW12O40/TiO2 catalysts for selective oxidation of dimethyl ether to dimethoxy dimethyl ether

An efficient rhenium oxide-modified H3PW12O40/TiO2 catalyst is found for a new synthesis of dimethoxy dimethyl ether from dimethyl ether oxidation. The effects of Re loading, H3PW12O40 content and different feedstocks on the performance of Re–H3PW12O40/TiO2 were investigated. The results showed that DMM2 selectivity was significantly improved up to 60.0%, with 15.6% of DME conversion over 5% Re–20% H3PW12O40/TiO2. NH3-TPD, NH3-IR, Raman spectra, H2-TPR, XPS and TEM were used to extensively characterize the structure and surface properties of the catalysts. The introduction of H3PW12O40 significantly affected the structure and reducibility of surface rhenium oxide species, in addition to increasing the acidity of the catalyst. The increased number of Lewis acid sites and weak acid sites and the optimal ratio of Re4+/Re7+ of Re–H3PW12O40/TiO2 were favorable for the formation of DMM2 from DME oxidation. The possible reaction pathway of DME oxidation to DMM2 was proposed.

Effects of the MoO3 structure of Mo–Sn catalysts on dimethyl ether oxidation to methyl formate under mild conditions

The selective oxidation of dimethyl ether (DME) to methyl formate (MF) was conducted in a fixed-bed reactor over the MoO3–SnO2 catalysts with different Mo/Sn ratios. The MF selectivity reached 94.1% and the DME conversion was 33.9% without the formation of COx over the MoSn catalyst at 433 K. The catalysts were deeply characterized by NH3-TPD, CO2-TPD, BET, XPS and H2-TPR. The characterization results showed that different compositions of catalysts obviously affected the surface properties of the catalysts, but the valence of the metal hardly changed with the Mo/Sn ratios. Raman spectroscopy, XRD and XAFS were further used to characterize the structure of the catalysts. The results indicated that the catalyst composition exerted a significant influence on the structure of MoO3. The formation of oligomeric MoO3 and the appropriate coordination numbers of Mo–O at 1.94 A are the main reasons for the distinct high catalytic activity of the MoSn catalyst.

Catalytic Oxidation of Dimethyl Ether to Dimethoxymethane over MnCl2-H4SiW12O40/SiO2 Catalyst

The H4SiW12O40/SiO2 heteropolyacid catalyst for the catalytic oxidation of dimethyl ether to dimethoxymethane was prepared by the impregnation method. MnCl2, SnCl4, and CuCl2 were used to modify the catalyst to improve its activity and selectivity. The catalytic oxidation reaction was carried out in a continuous flow fixed-bed reactor. H4SiW12O40/SiO2 is active for the oxidation of dimethyl ether, but the selectivity for dimethoxymethane is as low as 4.8%. Modification of H4SiW12O40/SiO2 with 5% MnCl2 significantly improves the dimethoxymethane selectivity up to 27.9% at 633 K, while SnCl4- and CuCl2-modified catalysts give dimethoxymethane selectivities of 16.4% and 0.4%, respectively, under the same conditions. The effects of the MnCl2 content (2%–20%) and the reaction temperature (573–633 K) on the reaction were investigated. A dimethyl ether conversion of 8.6% and a dimethoxymethane selectivity of 36.3% were obtained under the optimum conditions of 593 K and 5% MnCl2 content. X-ray diffraction patterns of the catalysts show that MnCl2 and H4SiW12O40 interact and are dispersed uniformly on the support. Infrared spectra demonstrate that the Keggin structure of H4SiW12O40 remains almost unchanged over the modified catalyst. Temperature-programmed desorption profiles of ammonia indicate that MnCl2 modification reduces the acidity of H4SiW12O40/SiO2 by decreasing the acid center numbers.

Effects of reaction atmosphere on dimethyl ether conversion to propylene process over Ca/ZSM-5

Abstract Effects of reaction atmospheres (nitrogen, carbon monoxide, carbon dioxide, syngas and water vapor) on stability of the catalyst, selectivities to propylene and byproducts for dimethyl ether conversion to propylene (DTP) over Ca/ZSM-5 were investigated in a continuous flow fixed-bed reactor. Besides, the regenerated catalyst was also studied for DTP process. The results show that the catalyst exhibits best stability, highest propylene selectivity and lowest selectivities to byproducts in carbon dioxide atmosphere, followed by nitrogen, carbon monoxide and syngas atmosphere, and water vapor atmosphere exerts worst effect on DTP. The catalytic performance of the regenerated catalyst also demonstrates that carbon dioxide as reaction atmosphere is most beneficial to DTP process.

Effects of tetrahedral molybdenum oxide species and MoOx domains on the selective oxidation of dimethyl ether under mild conditions

A new preparation method for MoO3–SnO2 catalysts precipitated by HNO3 was developed to selectively synthesize industrially useful chemicals formaldehyde and methyl formate via oxidation of environmentally friendly feedstock dimethyl ether. By adjusting the structure of MoO3–SnO2, the selectivity to formaldehyde and methyl formate can reach as high as 95.0% and 82.4%, respectively, under different conditions. The conclusion has been drawn, based on the experimental results, that the formation of tetrahedral molybdenum oxide species and SnMoO4 species favors the reaction of dimethyl ether to formaldehyde, and that the formation of MoOx domains favors the direct oxidation reaction of dimethyl ether to formaldehyde. The XRD and Raman results suggest that the formation of tetrahedral molybdenum oxide species has a positive correlation with the high selectivity to formaldehyde and indicates that the formation of the MoOx domains favors the high selectivity to methyl formate. The XPS results of the MoO3–SnO2 catalysts with different SnO2 contents demonstrate that formaldehyde is not readily desorbed from Mo1Sn2 and Mo1Sn3 because the electron-poor Mo cations of the domains supported on the surface of the catalysts strengthen their affinity for binding electron-donating dimethyl ether-derived intermediates and formaldehyde, which favors the subsequent reaction of formaldehyde to methyl formate. These interesting findings reveal that tetrahedral molybdenum oxide species and MoOx domains play an important role in the selective oxidation of dimethyl ether to formaldehyde and methyl formate, and give insight into the rational design of the MoO3–SnO2 catalyst structure for dimethyl ether oxidation in future studies.

Effects of MoO3 crystalline structure of MoO3–SnO2 catalysts on selective oxidation of glycol dimethyl ether to 1,2-propandiol

To improve the selectivity of 1,2-propandiol (PDO) by modifying the structure and morphology of the MoO3/SnO2 catalyst, orthorhombic (α), monoclinic (β) and hexagonal (h) MoO3 crystalline phases were prepared to investigate the rational design requirements of the MoO3–SnO2 structure that are beneficial for the reaction of glycol dimethyl ether (DMET) to PDO. With an increase in the reaction temperature, the highest PDO selectivity of the oxidation reaction of glycol dimethyl ether to 1,2-propandiol was always obtained over the h-MoO3–SnO2 catalyst and the lowest PDO selectivity was always obtained over the β-MoO3–SnO2 catalyst. The MoO3 bulk structure, the interaction between SnO2 and MoO3 and the surface properties of these three catalysts could account for this distinctive difference. Hexagonal MoO3 is dispersed more homogeneously over the h-MoO3–SnO2 catalyst due to the hexagonal crystalline tunnel structure existing in the h-MoO3–SnO2 catalyst, and the weak interaction between MoO3 and SnO2; besides, the more hydrated surface of the h-MoO3–SnO2 catalyst can lead to more Bronsted acid sites being present on the catalyst surface and favor the dissociation of the C–O bond in DMET and association of the C–C bond to form PDO with the assistance of the redox and basic sites, which can explain why the highest PDO was obtained over the h-MoO3–SnO2 catalyst. The lattice strain and oxygen vacancies in the β-MoO3–SnO2 catalyst, induced by the substitution of Sn4+ ions with the smaller sized Mo6+ ions, enhance the oxidation ability of the β-MoO3–SnO2 catalyst, and consequently more CH3O· can be formed and transformed to formaldehyde (FA) and methyl formate (MF), which can explain why the total selectivity of FA and MF was highest while the selectivity of PDO was lowest over the β-MoO3–SnO2 catalyst at the same time. These findings are pretty significant for further investigation of the rational design of the MoO3–SnO2 catalyst structure, applied to the conversion of DMET to PDO.

Tri-reforming of coal bed methane to syngas over the Ni-Mg-ZrO2 catalyst

Abstract Ni-ZrO 2 and Ni-Mg-ZrO 2 catalysts were prepared by a co-precipitation method, and then were characterized by BET, XRD, H 2 -TPR and CO 2 -TPD techniques. The performances of catalysts in the tri-reforming of coal bed methane to syngas were studied in a fixed bed reactor. The reaction conditions (temperature and feed gas composition) were mainly investigated. The results showed that at t =800°C, atmospheric pressure, CH 4 /CO 2 /H 2 O/O 2 /N 2 =1.0/0.45/0.45/0.1/0.4, GHSV=30000 mL·g −1 ·h −1 , about 99% of CH 4 conversion, 65% of CO 2 conversion, and V H2 / V CO of 1.5 could be achieved during 58 h of reaction, which are related to the strong metal-support interaction, the good thermal stability and basic nature of the catalyst. Furthermore, high temperature favors the tri-reforming of methane. By adjusting the feed gas composition, a specific V H2 / V CO could be achieved.

Ti-SBA-15 supported Cu–MgO catalyst for synthesis of isobutyraldehyde from methanol and ethanol

Ti-SBA-15 supported Cu and MgO catalysts were prepared and used for the first time in the one-step conversion of methanol and ethanol to isobutyraldehyde (IBA). The results show that the loadings of Cu and MgO, and catalyst calcination temperature have strong effects on the catalyst activity. A high yield of IBA, 32.7%, and high ethanol conversion, 96.6%, were achieved at 360 °C with WHSV of 3.0 mL (g−1 h−1) on the catalyst calcined at 400 °C when the loadings of Cu and Mg were 20.0 wt% and 6.5 wt%, respectively. The physicochemical properties of the catalysts were analyzed by various techniques including XRD, N2 adsorption and desorption, FT-IR, H2-TPR, CO2-TPD and XPS. The ordered mesoporous structure of the catalysts was retained with the introduction of CuO and MgO. The size of CuO particles on the catalysts was retained though they suffered from a varied calcination temperature. H2-TPR measurements revealed that the increase of calcination temperature from 400 °C to 700 °C resulted in the decrease of basicity of the catalysts, and enhanced the interaction between the Cu and Mg species and the support. The results from XPS analysis indicated that the binding energy of Cu 2p was increased with the introduction of MgO, while the increased calcination temperature easily resulted in the decrease of Cu content on the catalyst surface due to probable migration of Cu species into internal pores or their incorporation into the framework of the Ti-SBA-15 support.