Highly selective conversion of maleic anhydride to γ-butyrolactone over Ni-supported catalysts prepared by precipitation–deposition method

Abstract

The gas-phase hydrogenation of maleic anhydride over Ni catalysts supported on SiO2 and SiO2–Al2O3, prepared by incipient wetness impregnation (I) and constant-pH precipitation–deposition (PD), was studied. The samples were characterized by N2 adsorption at −196°C, X-ray diffraction, temperature-programmed reduction, H2 chemisorption, X-ray photoelectron spectroscopy, and transmission electron microscopy. The catalytic tests were carried out at atmospheric pressure, between 170 and 220°C and using a space-time of 12 ghmol−1. From the characterization results, it was determined that the interaction between Ni2+ species and the support strongly depends on the preparation method. The trend found for the Ni2+-support interaction was Ni/SiO2-PD >Ni/SiO2-Al2O3-PD > Ni/SiO2-I. After reduction in H2 flow, metal Ni particles were one order of magnitude smaller in catalysts prepared by precipitation–deposition than those prepared by impregnation. All catalysts were active for the hydrogenation of maleic anhydride (MA) into succinic anhydride (SA) and subsequent hydrogenolysis to γ-butyrolactone (GBL) and propionic acid (PA). Regardless of small amounts of CH4, no other products were detected at the reactor outlet. However, the activity and selectivity to GBL depends on the metal particle size, Ni-support interaction and the presence of Lewis acid sites on SiO2–Al2O3 surface. It was found that the small metallic particles obtained by precipitation–deposition method are more active and selective to GBL than the large particles formed using the impregnation method. The highest GBL yield (83%) was reached at 220°C with Ni/SiO2–Al2O3–PD, which is attributed to selective hydrogenolysis of SA adsorbed on Lewis acid sites by spillover of hydrogen chemisorbed on neighboring metal nickel nanoparticles.