Platinum-modified SiO2 with tubular morphology as efficient membrane-type microreactors for mineralization of formic acid

SiO2 amorphous tubes with the internal diameter ranging between 5 and 170 nm and having the aspect ratios typically >50, were prepared using DL-tartaric acid as inorganic template. The tubular SiO2 was impregnated with a platinum precursor (H2PtCl6), dried and then reduced with H2. The TEM, XPS, FTIR characterization methods revealed that platinum species were located preferentially on the inner walls of tubes having diameter smaller than 100 nm. The walls of SiO2 nanotubes proved to be amorphous and highly porous, the diameter of pores covering a wide range of radii. The macroporosity of the SiO2 tubes originated from the open ends of the tubes with the diameter ≥100 nm, whereas the pores located in the walls of tubes were responsible for the meso and microporosity. Finer Pt nanoparticles (0.9 nm average size) were obtained after the catalyst was dried in air in mild conditions compared to the catalytic material reduced with H2 (5.3 nm mean size) According to FTIR results, strong metal-support interaction was evidenced between platinum nanoparticles and inner walls of SiO2 nanotubes. In order to observe the effect of Pt nanoparticle morphology on catalytic behavior, the activity of platinum-modified SiO2 tubes (1 wt% Pt/SiO2) for the oxidation of formic acid to CO2 was investigated in the 20–75 °C temperature range. The catalytic activity–morphology relationship of Pt/SiO2 nanotubes was studied and the results were explained in light of experimental results. The catalytic experiments revealed for the first time that SiO2 nanotubes with highly permeable walls behave as efficient membrane-type microreactors for the oxidation of formic acid to CO2. This type of morphological-dependent catalysis may prove to be an efficient tool in near future for the abatement of pollutants in liquid phase.