Hydrothermal stability and catalytic activity of aluminum-containing mesoporous ethane-silicas

Aluminum was incorporated into the mesoporous framework of ethane-silica by one-pot condensation of Al(OiPr)(3) with 1,2-bis(trimethoxysilyl)ethane using octadecyltrimethylammonium chloride as surfactant. Powder X-ray diffraction patterns, nitrogen sorption analysis, and TEM results reveal the formation of an ordered mesoporous material with uniform porosity. Al-27 MAS NMR confirms the incorporation of aluminum in the framework. The synthesized materials exhibit extremely high hydrothermal stability in boiling water (no obvious change of mesostructure and textural properties was observed even after refluxing in water for 100 h), which could be mainly contributed to the ethane-bridged mesoporous framework. The aluminum-containing mesoporous ethane-silicas are efficient catalysts for the alkylation of 2,4-di-tert-butylphenol by cinnamyl alcohol to yield a flavan.

Novel catalysis of TiO2 for the catalytic alcohols synthesis from CO and H2O

Direct synthesis of alcohols from CO and H2O was investigated using TiO2 catalyst. MeOH (about 24 mg g(-1) h(-1)) and EtOH (about 8 mg g(-1) h(-1)) could be produced under the reaction conditions of T= 573 K, P= 0.5 MPa, CO flow rate of 30 ml min(-1) and CO/H2O = 3/2 during the period of 12 to 44 h time-on-stream. Compared with PbO, TiO2 could preserve stable catalytic activity during a long time of reaction. For the same catalyst TiO2, the reaction performance of alkali carbonates increased with their solubility (K2CO3>Na2CO3>Li2CO3). The corresponding catalytic activity was found to increase with the alkalescence of solvent. The formation mechanism of alcohols was proposed as well. (C) 2004 Elsevier B.V. All rights reserved.

Catalytic alcohols synthesis from CO and H2O on TiO2 catalysts calcined at various temperatures

The reaction performance for CO hydration on a TiO2 catalyst under different calcination temperatures was investigated. Under reaction conditions of T = 573 K, P = 0.5 MPa, CO flow rate of 30 ml min(-1), TOS = 12 h, and CO/H2O (g) = 3/2 (mol), the TiO2 catalyst with a futile content of 18% shows a maximum alcohols STY of 1.81 Mg m(-2) h(-1). In addition, the catalyst deactivation and regeneration were discussed.

A novel method for preparing PEMFC catalytic layers

A novel PEMFC catalytic layer was fabricated by a Nafion-pyrolyzed method, which demonstrated a high performance with a maximum power density of 0.82 W/cm(2) on an electrode prepared by this method. The effects of the heat-treatment temperature and Nation content in the catalyst layer on performance were studied.

Investigation on the catalytic roles of silver species in the selective catalytic reduction of NOx with methane

Silver impregnated H-ZSM-5 zeolite catalysts with silver loading from 3 to 15 wt.% were investigated for the selective catalytic reduction (SCR) of NOx with CH4 in the excess of oxygen. X-ray diffraction (XRD) and UV-Vis measurements established the structure of silver catalysts. A relationship between the structure of silver catalysts and their catalytic functions for the SCR of NOx by CH4 was clarified. The NO conversion to N-2 showed a S-shape dependence on the increase of Ag loading. No linear dependence of catalytic activity on the amount of silver ions in the zeolite cation sites was observed. Contrastively, the activity was significantly enhanced by the nano-sized silver particles formed on the higher Ag loading samples (greater than or equal to7 wt.%). Temperature programmed desorption (TPD) and temperature programmed reduction (TPR) studies showed that nano-silver particles provided much stronger adsorption centers for active intermediates NO3-(s) on which adsorbed NO3-(s) could be effectively reduced by the activated methane. Silver ions in the zeolite cation sites might catalyze the reaction through activation of CH4 at lower temperatures. Activated CH4 reacted with NO3-(s) adsorbed on nano-silver particles to produce N-2 and CO2. (C) 2003 Elsevier B.V. All rights reserved.

Solid-state MAS NMR studies on the hydrothermal stability of the zeolite catalysts for residual oil selective catalytic cracking

By using the solid-state MAS NMR technique, the hydrothermal stabilities (under 100% steam at 1073 K) of HZSM-5 zeolites modified by lanthanum and phosphorus have been studied. They are excellent zeolite catalysts for residual oil selective catalytic cracking (RSCC) processes. It was indicated that the introduction of phosphorus to the zeolite via impregnation with orthophosphoric acid led to dealumination as well as formation of different Al species, which were well distinguished by Al-27 3Q MAS NMR. Meanwhile, the hydrothermal stabilities of the zeolites (P/HZSM-5, La-P/HZSM-5) were enhanced even after the samples were treated under severe conditions for a prolonged time. It was found that the Si-O-Al bonds were broken under hydrothermal conditions, while at the same time the phosphorous compounds would occupy the silicon sites to form (SiO)(x)Al(OP)(4 - x) species. With increasing time, more silicon sites around the tetrahedral coordinated Al in the lattice can be replaced till the aluminum is completely expelled from the framework. The existence of lanthanum can partially restrict the breaking of the Si-O-Al bonds and the replacement of the silicon sites by phosphorus, thus preventing dealumination under hydrothermal conditions. This was also proved by P-31 MAS NMR spectra. (C) 2004 Elsevier Inc. All rights reserved.

On the surface sites Of MOP/SiO2 catalyst under sulfiding conditions: IR spectroscopy and catalytic reactivity studies

The surface sites of MoP/SiO2 catalysts and their evolution under sulfiding conditions were characterized by IR spectroscopy using CO as the probe molecule. The HDS activities of thiophene were measured on the MoP/SiO2 catalyst that was subjected to different sulfidation and reactivation pretreatments. Cus Modelta+ (0 < delta less than or equal to 2) sites are probed on the surface of fresh MoP/SiO2 by molecularly adsorbed CO, exhibiting a characteristic IR band at 2045 cm(-1). The surface of MoP/SiO2 is gradually sulfided in HDS reactions, as revealed by the shift of the IR band at 2045 to ca. 2100 cm(-1). Although the surface of a MoP/SiO2 catalyst becomes partially sulfided, the HDS activity tests show that MoP/SiO2 is fairly stable in the initial stage of the HDS reaction, providing further evidence that molybdenum phosphide is a promising catalytic material for industrial HDS reactions. Two kinds of surface sulfur species are formed on the sulfided catalyst: reversibly and irreversibly bonded sulfur species. The MoP/SiO2 catalyst remains stable in the HDS of thiophene because most sulfur species formed under HDS conditions are reversibly bonded on the catalyst surface. A detrimental effect of presulfidation on the HDS activity is observed for the MoP/SiO2 catalyst treated by H2S/H-2 at temperatures higher than 623 K, which is ascribed to the formation of a large amount of the irreversibly bonded sulfur species. The irreversibly sulfided catalyst can be completely regenerated by an oxidation and a subsequent reduction under mild conditions. (C) 2003 Elsevier Inc. All rights reserved.

Correlation between the characteristics and catalytic performance of Ni-V-O catalysts in oxidative dehydrogenation of propane

Ni - V - O series catalysts for the oxidative dehydrogenation (ODH) of propane were prepared and characterized by BET, XRD, H-2- TPR, O-2-TPD-MS and electrical conductivity. At 425 degreesC a C3H6 selectivity of 49.9% was observed on Ni0.9V0.1OY at a C3H8 conversion of 19.4%, and the obtained selectivity is almost two times higher than that over NiO at the roughly same conversion of C3H8. The mobile oxygen species created by the interaction of NiO and V2O5 has been found in the composite catalysts by O-2-TPD-MS and electrical conductivity studies, which seems to be responsible for the enhanced selectivity of the propane oxidative dehydrogenation.