Vilas Hari Rane

Selective oxidation of methane to CO and H2 over unreduced NiO-rare earth oxide catalysts

NiO-LnOx (Ln = lanthanide) catalysts (with Ni∶Ln=1∶1) without prereduction show high activity/selectivity and very high productivity in the oxidative conversion of methane to CO and H2. The catalysts are first activated in the initial reaction, which is started at 535–560°C, by the reduction of NiO and creation of active sites. The carbon deposition on the catalysts in the reaction, particularly for the NiO-Gd2O3, NiO-Tb4O7 and NiO-Dy2O3 catalysts, is quite fast but it has caused a little or no influence on the catalytic activity/selectivity. Pulse reaction of pure methane on NiO-Nd2O3 (at 600°C) shows involvement of lattice oxygen in the initial reaction and also reveals formation of carbon from CO on the catalyst reduced in the reaction.

Low temperature oxidative conversion of methane to synthesis gas over Co/rare earth oxide catalysts

CoO-rare earth oxide catalysts (particularly CoO-Yb2O3) show high activity and selectivity in the oxidative conversion of methane to CO and H2 with very high productivity at low temperatures (⩽ 700 °C as low as 300 °C).

Surface basicity and acidity of alkaline earth‐promoted La2O3 catalysts and their performance in oxidative coupling of methane

The catalytic activity and selectivity of La 2 O 3 and alkaline earth (viz. Mg, Ca, Sr and Ba) promoted La 2 O 3 (alkaline earth metal/La = 0.1) catalysts in the oxidative coupling of methane (OCM) to C 2 -hydrocarbons (at 800°C, CH 4 /O 2 ratio = 4 or 8 and gas hourly space velocity = 102000 cm 3 g -1 h -1 ) have been investigated. The acidity and basicity distributions on these catalysts are measured by the temperature programmed desorption (TPD) of NH 3 and CO 2 from 50°C to 950°C, respectively. Both the acidity and basicity of the La 2 O 3 catalysts and their activity in the OCM are strongly influenced by the alkaline earth promoter and its concentration. Among the catalysts, Sr-promoted La 2 O 3 (Sr/La = 0.1) is the most active and selective catalyst for the OCM process. This catalyst contains a larger number of strong basic sites and intermediate strength acid sites.

Oxidative coupling of methane and oxidative dehydrogenation of ethane over strontium-promoted rare earth oxide catalysts

Sr-promoted rare earth (viz. La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb) oxide catalysts (Sr/rare earth ratio = 0.1) are compared for their performance in the oxidative coupling of methane (OCM) to C 2 hydrocarbons and oxidative dehydrogenation of ethane (ODE) to ethylene at different temperatures (700 and 800°C) and CH 4 (or C 2 H 6 )/O 2 ratios (4-8), at low contact time (space velocity = 102000 cm 3 g -1 h -1 ). For the OCM process, the Sr-La 2 O 3 catalyst shows the best performance. The Sr-promoted Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 and Er 2 O 3 catalysts also show good methane conversion and selectivity for C 2 hydrocarbons but the Sr-CeO 2 and Sr-Dy 2 O 3 catalysts show very poor performance. However, for the ODE process, the best performance is shown by the Sr-Nd 2 O 3 catalyst. The other catalysts also show good ethane conversion and selectivity for ethylene; their performance is comparable at higher temperatures (≥800°C), but at lower temperature (700°C) the Sr-CeO 2 and Sr-Pr 6 O 11 catalysts show poor selectivity.

Influence of various promoters on the basicity and catalytic activity of MgO catalysts in oxidative coupling of methane

Addition of promoters, such as Li2O, Na2O, PbO, La2O3, MgCl2 and CaCl2, to MgO causes a large increase in its surface basicity (particularly strong basic sites) and catalytic activity/selectivity in oxidative coupling of methane, but the correlation between the basicity and C2-yield is poor, indicating that factors other than basicity are also important in deciding catalytic performance.

Role of cation–anion cooperation in the selective synthesis of glycidol from glycerol using DABCO–DMC ionic liquid as catalyst

Transesterification of dimethyl carbonate with glycerol has been investigated using 1,4-diazabicyclo [2.2.2] octane (DABCO) based ionic liquid as a catalyst. DABCO reacted with dimethyl carbonate to form ionic liquid as the reaction progressed. Though the basicity of DABCO based ionic liquid was lower than that of DABCO, the catalytic activity and selectivity to glycidol was higher with DABCO based ionic liquid as a catalyst, indicating that basicity may not be the only criterion in deciding activity and selectivity of the reaction. The cooperative effect of the cation and anion of the ionic liquid is responsible for the observed results. The best results (97% glycerol conversion with 83% selectivity to glycidol and 17% selectivity to glycerol carbonate) were obtained using DABCO based ionic liquid as a catalyst. A plausible mechanism involving the role of both the cation and anion of the ionic liquid has been proposed.

Oxidative coupling of methane over La-promoted CaO catalysts: influence of precursors and catalyst preparation method

Abstract The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO (La/Ca = 0.05) catalysts, prepared using different precursor salts for CaO and La2O3 (viz. acetates, carbonates, nitrates and hydroxides) and catalyst preparation methods (viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent), under different reaction conditions (temperature: 700-850 °C, CH4/O2 ratio: 4.0 and 8.0, and GHSV: 51360 cm3 ·g−1 ·h−1). The surface area and surface basicity/base strength distribution of the catalysts have also been investigated. The surface properties and catalytic activity/selectivity of the La-promoted CaO catalysts vary from catalyst to catalyst depending on the catalyst precursors used and catalyst preparation method. The basicity/base strength distribution is strongly influenced by the precursors (for CaO and La2O3) and catalyst preparation method. Basicity (total and strong basic sites measured in terms of CO2 chemisorbed at 50 °C and 500 °C, respectively) observed for the catalyst prepared by co-precipitation method is higher than that of the catalysts prepared by physical mixing method. The catalysts prepared by the nitrates of La- and Ca- and co-precipitated by the solution of sodium carbonate and ammonium carbonate exhibit different catalytic performance in OCM. The finding that no direct relationship between the surface basicity and catalytic activity/selectivity in OCM exists indicates that basicity is not solely responsible for obtaining high selectivity to C2 hydrocarbons.

Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Abstract Surface properties (viz. surface area, basicity/base strength distribution, and crystal phases) of alkali metal doped CaO (alkali metal/Ca = 0.1 and 0.4) catalysts and their catalytic activity/selectivity in oxidative coupling of methane (OCM) to higher hydrocarbons at different reaction conditions (viz. temperature, 700 and 750°C; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140–20550 cm3·g−1·h−1) have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties (viz. surface area, basicity/base strength distribution) and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity (strong basic sites) and the C2+ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO (Na/Ca = 0.1, before calcination) catalyst (calcined at 750°C), showed best performance (C2+ selectivity of 68.8% with 24.7% methane conversion), whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.

Oxidative coupling of methane to C2-hydrocarbons over La-promoted CaO catalysts

La2O3 promoted CaO [La/Ca (mol/mol) = 0.05] catalyst shows very high activity and selectivity (methane conversion: 25%, C2-selectivity: 66% and C2-space-time-yield: 864 mmol ·g−1 (cat.)·h−1) with no catalyst deactivation in oxidative coupling of methane to C2-hydrocarbons at 800 ° C.

Comparison of alkali metal promoted MgO catalysts for their surface acidity/basicity and catalytic activity/selectivity in the oxidative coupling of methane

Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0.1) calcined at 750°C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C 2 -hydrocarbons at different temperatures (700-750°C), CH 4 /O 2 ratios (4.0 and 8.0) in feed, and space velocities (10320 cm 3 g -1 h -1 ). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C 2 -hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750°C, the best performance in the OCM is shown by Li-MgO (at 750°C).