Sopan T. Chaudhari

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.

Influence of precursors of Li2O and MgO on surface and catalytic properties of Li‐promoted MgO in oxidative coupling of methane

The influence of the catalyst precursors (for Li2O and MgO) used in the preparation of Li-doped MgO (Li/Mg = 0.1) on its surface properties (viz basicity, CO2 content and surface area) and activity/selectivity in the oxidative coupling of methane (OCM) process at 650-750°C (CH4/O2 feed ratio = 3.0-8.0 and space velocity = 5140-20550 cm3 g-1 h-1) has been investigated. The surface and catalytic properties are found to be strongly affected by the precursor for Li2O (viz lithium nitrate, lithium ethanoate and lithium carbonate) and MgO (viz magnesium nitrate, magnesium hydroxide prepared by different methods, magnesium carbonate, magnesium oxide and magnesium ethanoate). Among the Li-MgO (Li/MgO = 0.1) catalysts, the Li-MgO catalyst prepared using lithium carbonate and magnesium hydroxide (prepared by the precipitation from magnesium sulfate by ammonia solution) and lithium ethanoate and magnesium acetate shows high surface area and basicity, respectively. The catalysts prepared using lithium ethanoate and magnesium ethanoate, and lithium nitrate and magnesium nitrate have very high and almost no CO2 contents, respectively. The catalysts prepared using lithium ethanoate or carbonate as precursor for Li2O, and magnesium carbonate or ethanoate, as precursor for MgO, showed a good and comparable performance in the OCM process. The performance of the other catalysts was inferior. No direct relationship between the basicity of Li-doped MgO or surface area and its catalytic activity/selectivity in the OCM process was, however, observed.

Hydrogenation of crotonaldehyde to n-butyraldehyde: reaction kinetics in a slurry reactor

Hydrogenation of crotonaldehyde was studied in liquid phase using Pd/C catalyst. The only product formed was n-butyraldehyde under the reaction conditions of the present work. The concentration-time profiles were obtained under various operating conditions. The rate constants were evaluated by simulating the concentration-time plots. The model predictions and the experimental data were found to be in good agreement.