Decomposition of formic acid over Ni-containing SiO2 catalysts synthesized by various one-pot synthesis routes

In this study SiO2 supported catalysts with different nickel amounts [5Ni–SiO2 (P123), 2,5Ni–SiO2 (P123), 5Ni–SiO2 (NH3-CA), 5Ni–SiO2 (Tw80–NaF) and 5Ni–SiO2 (Tw80)] were synthesized with four different one-pot synthesis routes. These catalysts were characterized by XRD, ATR/FT–IR, SEM–EDS, N2 adsorption–desorption analysis and tested for hydrogen production from catalytic gas-phase decomposition of formic acid. XRD and ATR/FT-IR results confirmed the presence of a metallic Ni phase in the catalysts. It was seen that the catalysts synthesized with surfactant Pluronic 123 (P123) exhibited the highest surface area. The N2 adsorption–desorption isotherms of the catalysts other than 5Ni–SiO2 (Tw80–NaF) were consistent with Type IV according to the IUPAC classification. Pore structure deterioration was observed in catalysts synthesized using Tw80–NaF and synthesized by the surfactant-free one-pot method [5Ni–SiO2 (NH3-CA)]. The highest H2 selectivity was observed at 350 °C for empty reactor and it was decided to conduct the activity test studies of the catalysts at this temperature. All catalysts exhibited complete formic acid conversion at 350 °C. The Lewis acidity order of the catalysts was found to be 2.5Ni–SiO2 (P123) > 5Ni–SiO2 (Tw80) > 5Ni–SiO2 (NH3-CA) > 5Ni–SiO2 (P123). The highest H2 concentration and selectivity were obtained with the 5Ni–SiO2 (P123) catalyst. As a result, it was determined that the acidic-basic property of the catalyst may be more dominant than the other properties (pore properties, surface area, Ni crystallite size) on the catalytic activity in hydrogen production from formic acid.