Comparative catalytic evaluation of nickel and cobalt substituted phosphomolybdic acid catalyst supported on silica for hydrodesulfurization of thiophene

Phosphomolybdic acid supported on silica (PMoA), and phosphomolybdic acid supported on silica substituted with nickel (Ni-PMoA), cobalt (Co-PMoA), are prepared with different loadings. All catalysts have been characterized using thermogravimetric analysis (TGA), BET surface area, Solid-state 31P NMR spectra, FT-IR, Diffuse Reflectance Infrared Fourier Transform (DRIFT) and Powder X-ray diffraction analysis (XRD). The surface areas of the catalysts are slightly lower than the surface area of the silica used in making these catalysts, while the XRD studies indicated the amorphous nature of the prepared catalysts. All catalysts are tested for their activity in the hydrodesulfurization of thiophene in the temperature range of 300-500 °C. Under similar conditions the silica supported catalyst i.e. PMoA, showed lower hydrodesulfurization activity, compared to the nickel and cobalt substituted heteropoly acids, i.e. Ni-PMoA and Co-PMoA, indicating enhancement of catalytic activity with substitution of nickel and cobalt. Moreover, the nickel-substituted catalyst, Ni-PMoA, showed slightly higher activity than the cobalt-substituted ones, Co-PMoA. At 500 °C, Ni-PMoA gave a 99.6% HDS conversion of thiophene whereas the Co-PMoA yielded a 98.3%. HDS conversion of thiophene. Brønsted/Lewis acidity of the catalyst precursor appear to be essential for the catalytic hydrodesulfurization.