Jianzhong Niu

Influence of SnO2-doped W-Mn/SiO2 for oxidative conversion of methane to high hydrocarbons at elevated pressure

The SnO2-doped 5% Na2WO4-2% Mn2O3/SiO2 catalyst for oxidative conversion of methane to high hydrocarbons has been studied in a micro-stainless-steel reactor at elevated pressure. At 1053 K, 1.0 t 105 hm1 GHSV and 0.6MPa, a CH4 conversion of 33.0% with C2+ selectivities of 73.1% is obtained; here the C2, C3 and C4 hydrocarbons selectivities of 36.8, 14.2 and 22.1% are observed. On addition of SnO2, conversion of methane and selectivities of C3nC4 hydrocarbons increase obviously. The observed results showthe storage-oxygen capability in Na-W-Mn/SiO2 catalyst is enhanced with adding SnO2, for Mn and Na2WO4 migrate to near-surface to result in a marked shift to higher molecular weight products. The distribution of products at the operating conditions and content of SnO2 loading has been described.

Mechanistic study of oxidative coupling of methane over Mn2O3Na2WO4SiO2 catalyst

Abstract EPR and Raman spectroscopies have been used to characterize the active oxygen species on Mn 2 O 3  Na 2 WO 4 SiO 2 . The results show that the lattice oxygen O2− is responsible for the activation of methane. F-centers with an EPR parameter g = 2.0046 form when gas-phase oxygen is admitted at room temperature onto the catalyst reduced with methane at 800°C. Molecular oxygen plays an inducing role in the two-electrons transfer from W4+ to the oxygen ion vacancy which is produced by methane reduction. The EPR peak at g = 2.0046 disappears with increasing temperature. Raman spectra give further information about the production of O2− from molecular oxygen. For the catalyst reduced with methane, no Raman lines are observed, because the top WO bonds are broken by the reduction, WOSi species are slightly ionic, and they are Raman inactive. When the temperature is increased to 80°C in the presence of gas-phase oxygen, Raman lines are obtained which are the same as those of the catalyst before reduction. No OO stretching modes are observed. We suggest that molecular oxygen is activated by an F-center to produce lattice oxygen O2−. A possible redox model for the Mn 2 O 3  Na 2 WO 4 SiO 2 catalyst has been proposed.

Characterization of TiO2-, ZrO2- and Al2O3-supported iron catalysts as used for CO2 hydrogenation

Alumina-, titania- and zirconia-supported iron oxides with an Fe loading of 5 wt.-% have been prepared by direct reduction of the precursors from incipient wetness impregnation and used for the synthesis of C2+-hydrocarbons from CO2 and H2. According to the conversion of CO2, the catalytic activity decreases in the following order: FeTiO2(B) ∼ FeZrO2(B)>FeTiO2(A)>FeZrO2(A)>FeAl2O3. XRD, Raman, Mossbauer and EXAFS analyses are employed for the characterization of the catalysts following the reduction treatment. The results suggest that conversion of CO2 to hydrocarbons is favored by the simultaneous presence of both zerovalent irons and coordinatively unsaturated cationic irons, among which ferric ions are for the Fe/ZrO2(B) and ferrous ions for the Fe/TiO2(B).

Oxidative coupling of methane over Na-Mn-W/SiO2 catalyst at higher pressure

Na-Mn-W/SiO2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH4 conversion of 15.1% with a C2+ selectivity of 71.8% was obtained under 750oC, 1.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH4 conversion with 51.6% C2 selectivity and 23.6% C3-C4 selectivity was obtained under 750oC, 2.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa.

CeO2-Promoted W-Mn/SiO2 catalysts for conversion of methane to C3–C4 hydrocarbons at elevated pressure

A CeO2-doped Na-Mn-W/SiO2 catalyst for oxidative conversion of methane has been studied in a micro-stainless-steel reactor under elevated pressure; a CH4 conversion of 47.2% with a C3-C4 selectivity of 47.3% (C2:C3:C4 = 1:1:3.3) was obtained at 983 K with 1.0 x 10(5) ml g-1 h-1 GHSV, CH4/O2 = 2.5 and P = 0.6 MPa.

Influence of ZrO2 on Carbon Monoxide Oxidation Over Pd/Al2O3

The influence of ZrO2 on the properties of Al2O3 and performances of Pd/Al2O3 catalyst in CO oxidation have been investigated. TPD results show that the activity enhanced is due to the increase of the adsorptive capacity of CO and the activation of C=O bond after the introduction of ZrO2.