Zhusheng Xu

Promotional effect of Pt on non-oxidative methane transformation over Mo-HZSM-5 catalyst

The influence of modification of Mo-HZSM-5 catalyst by Pt on methane non-oxidative transformation to ethylene and aromatics is investigated. Carbon accumulation on the catalyst is studied by means of DTA and TG methods. It is demonstrated that the addition of Pt to Mo-HZSM-5 considerably enhances the catalyst stability and reduces the carbon deposition on the catalyst. In the meanwhile, Mo-HZSM-5 is shown not to be a good catalyst for methane non-oxidative conversion because the total efficiency for methane conversion to useful products is even lower than it is in the oxidative coupling process.

The chemical status of indium in indium impregnated HZSM-5 catalysts for the SCR of NO with CH4

Abstract TPR and NH 3 -TPD experimental results suggested that there was a strong interaction between surface indium species and the protonic acid sites of HZSM-5 zeolite during the preparation of In/HZSM-5 catalysts with conventional wetness impregnation method. A mechanism for the reduction of indium species on In/HZSM-5 catalysts has been proposed.

Selective catalytic reduction of nitrogen monoxide with methane over impregnated In/HZSM-5 in the presence of excess oxygen

In/HZSM-5 catalyst prepared by the impregnation method was active for NO reduction with methane. Complete reduction of NO was obtained at 450°C over an In/HZSM-5 catalyst. The presence of oxygen in the feed greatly enhanced the NO reduction activity of In/HZSM-5. Co/HZSM-5 and Ga/HZSM-5 were less effective than In/HZSM-5. Cu/HZSM-5, In/Na-ZSM-5 and In2O3/Al2O3 were ineffective for NO reduction with CH4. The NO reduction activity was proportional to the level of indium impregnated onto HZSM-5 but excess amounts of indium were detrimental to the catalytic activity. Phase analysis by XRD measurements demonstrated that there was a threshold value in the indium content, i.e., the maximum dispersion capacity of indium oxides. It is concluded that highly dispersed indium species are the active centers for the selective catalytic reduction of NO with CH4.

Preparation of Mn substituted La-hexaaluminate catalysts by using supercritical drying

LaMnxAl12−xO19 catalysts were prepared from NH4OH and metal nitrates solutions. Supercritical drying (SCD) and conventional oven drying (CD) methods were used to extract the water in the hydrogel. The effects of drying methods on properties of the catalysts were investigated by means of TEM, N2-adsorption, thermogravimetry (TG)–differential thermal analysis (DTA) and X-ray diffraction. SCD method is beneficial to maintain high surface area and improving catalytic activity for methane combustion of the catalyst. The specific surface area and pore volume of LaMn 1Al11O19 catalyst prepared by SCD method are 28 m 2 /g and 0.23 cm 3 /g, respectively, and the ignition of methane could be carried out at 450 ◦ C. However, those of the CD catalyst prepared from the same precursor are 15 m 2 /g, 0.11 cm 3 /g and 530 ◦ C, respectively. Suitable Mn content (0 ≤ x ≤ 2) could promote the formation of LaMnAl11O19 hexaaluminate, while further addition of Mn (2

Surface structure and reaction performances of highly dispersed and supported bimetallic catalysts

Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of Mossbauer spectroscopy, Pt-L111-edge EXAFS and Hz-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the γ-Al2O3 surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the γ-A1203, surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, namedM1 sites and M2 sites. M1 sites are the sites in which Pt directly anchored on the γ-Al2O3 surface, while M2 sites are those in which Pt anchored on the metal oxide surface. MI sites are favorable for low temperature H2 adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M2 sites which adsorb more H2 at higher temperature, are more resistant to the deactivation due to less carbon deposition, and provide major contribution to the dehydrogenation reaction.

Methane aromatization in the absence of an added oxidant and the bench scale reaction test

A bench scale reaction test for methane aromatization in the absence of an added oxidant was performed and its reaction result evaluated based on the carbon balance of the system. The result was compared with those obtained from the micro‐reaction test to ensure the accuracy of the internal standard analyzing method employed in this paper. The catalytic performances of modified Mo/HZSM‐5 catalysts were examined. It was found that pre‐treatment by steam on HZSM‐5 weakened the serious deposition of coke, and pre‐impregnation of n-ethyl silicate on HZSM‐5 could improve the conversion of CH4, but had little effect on coke formation. A low temperature activation procedure including pre‐reduction of the catalyst with methane prevents the zeolite lattice from being seriously destroyed by high valence state Mo species when the Mo loading is high. It was suggested that Mo2C species detected by XRD spectra was the active phase for CH4 aromatization.

Interaction of methane with surfaces of silica, aluminas and HZSM-5 zeolite. A comparative FT-IR study

Infrared investigations on the interaction of methane with silica, aluminas (η,γ and α) and HZSM-5 zeolite have been carried out. At low temperature (173 K), methane adsorption was observed over these oxides and HZSM-5 zeolite. Our findings featured that the infrared inactiveΝ1 band (2917 cm−1) of a gaseous methane molecule became active and shifted to lower frequencies (2900 and 2890 cm−1) when it adsorbed on the surfaces of these adsorbents. Our results also demonstrate that hydroxyl groups played a very important role in methane adsorption over the acidic oxides and the HZSM-5 zeolite. When interaction between the hydroxyl groups and methane took place, the band shift of the hydroxyl groups varied with different oxides. The strength of the interaction decreased according to the following sequence, Si-OH-Al>Al-OH>Si-OH, which is in accordance with the order of their acidities. At higher temperatures, methane interacted quite differently with various oxides and HZSM-5 zeolite. It has been observed that the hydroxyl groups of silica, γ-alumina and HZSM-5 zeolite could exchange with CD4 at temperatures higher than 773K, while those on η-alumina could exchange at a temperature as low as 573 K. Another interesting observation was the formation of formate species over Al2O3 (both η and γ) at temperatures higher than 473 K. The formate species would decompose to CO2, or produce carbonate at much higher temperatures. Formation of formate species was not observed over silica and HZSM-5 under similar conditions, α-Al2O3 did not adsorb or react with methane in any case.

A study on reduction behaviors of the supported platinum-iron catalysts

Abstract The reduction behaviors of the supported platinum–iron catalysts and their comparison with supported iron catalysts were studied by TPR (temperature-programmed reduction)–in situ 57 Fe MBS (Mossbauer spectroscopy). The results indicated that the TPR processes of all Fe-containing catalysts were different from that of bulk α-Fe2O3. There were interactions between Pt, Fe and the γ-Al2O3 or SiO2 support for the Pt–Fe/γ-Al2O3 and Pt–Fe/SiO2 catalysts. All the iron-containing catalysts show that Fe3+ was highly dispersed on the support (γ-Al2O3 and SiO2) before reduction. No Fe0 was found in the reduction processes. The Fe3+ was reduced to Fe2+ in tetrahedral vacancy first for the reduction of the Pt–Fe/γ-Al2O3 catalyst. No Fe2+ in octahedral vacancy was found in the reduction of the Pt–Fe/SiO2 catalyst. Adding Pt to Fe/support (γ-Al2O3 or SiO2) could promote the reduction of the Fe species.

Synthesis of the high-surface-area CexBa1−xMnAl11Oy catalyst in reverse microemulsions using inexpensive inorganic salts as precursors

The high-surface-area CexBa1−xMnAl11Oy (x = 0, 0.1, 0.2, 0.3) catalysts were synthesized in the nonionic reverse microemulsion (ME), using the inorganic salts as the reactants. The supercritical drying (SCD) and conventional oven drying (CD) methods were used to remove the water in hydrogels, respectively. The CexBa1−xMnAl11Oy samples were characterized by N2-adsorption, transmission electron microscopy (TEM), TGA-DTA, and X-ray powder diffraction (XRD). The effects of the microemulsion composition, the drying method, the calcination temperature and the introduction of Ce on the catalysts were investigated. The results showed that the morphology of the catalyst was controlled by the microemulsion microstructure; and the homogeneity of the precursor was improved effectively by the reverse microemulsion method and the supercritical drying method. Due to the high homogeneity of the precursors, the initial formation temperature of the hexaaluminate phase decreased to lower than 1100 °C. The BaMnAl11O19 catalyst had high surface area (72.4 m2 g−1) and high catalytic activity (T10 = 445 °C) for methane combustion. When Ce was introduced, the CexBa1−xMnAl11Oy catalyst (x = 1) had the higher activity (T10 = 430 °C) than that of the BaMnAl11O19 one due to a synergetic effect between Ce and Mn.

Formation of a novel type of reverse microemulsion system and its application in synthesis of the nanostructured La0.95Ba0.05MnAl11O19 catalystElectronic supplementary information (ESI) available: Table 1, Figs. 1b, 5, 6 and 7. See http://www.rsc.org/suppdata/cc/b4/b404133j/

In the study, a novel microemulsion system, consisting of water, iso-propanol and n-butanol, was developed to synthesize the nanostructured La(0.95)Ba(0.05)MnAl(11)O(19) catalyst with high surface area and catalytic activity for methane combustion.