Silica hybrid gel catalysts containing ruthenium complexes:: influence of reaction parameters on the catalytic behaviour in the synthesis of N,N-dimethylformamide from carbon dioxide

The synthesis of N,N-dimethylformamide from carbon dioxide, hydrogen and dimethylamine has been studied in an autoclave using a sol-gel derived heterogeneous catalyst made of RuCl2{PPh2(CH2)(2)Si(OEt)(3)}(3) and Si(OEt)(4) in a ratio of 1:50. The effect of the reaction variables on the activity and selectivity of the hybrid gel was examined by varying the initial concentrations of the catalyst and dimethylamine, the partial pressures of hydrogen and carbon dioxide, the temperature and the stirring frequency. Parametric investigations revealed that the measured reaction rates are not disguised by mass transfer phenomena under the conditions applied. The suitable temperature range of the reaction is between 370 and 400 K, with the upper temperature limit given by the thermal stability of the catalyst. Hydrogen appeared to be the Limiting reactant since it significantly influenced the reaction rate. In contrast, the carbon dioxide partial pressure in the range 3-18 MPa and the dimethylamine concentration had only a negligible effect on the turnover frequency, indicating a zeroth order dependence. High concentrations of hydrogen and carbon dioxide in the Liquid dimethylamine phase afford high concentrations of all reactants at the catalytic centres in an ideal reaction design. (C) 1999 Elsevier Science B.V. All rights reserved.