Synthesis of nanosized thin-film bimetallic catalysts based on mesoporous TiO2 for microstructured reactors

Abstract

A synthetic procedure for the production of effective catalysts for the selective hydrogenation of organic substrates was developed, and the samples of thin-film Pt-Sn/TiO2 materials, which are characterized by high dispersity and a narrow size distribution of bimetallic particles in a mesoporous matrix of titanium dioxide, were prepared. With the use of a set of physicochemical techniques (low-temperature nitrogen adsorption, X-ray diffraction analysis, thermal analysis, and transmission electron microscopy), the formation and surface properties of the mesoporous Pt-Sn/TiO2 materials as powder and coatings on the surfaces of silica capillaries and plates were studied. Based on the effects of the sol composition and calcination temperature on the texture properties of TiO2, an optimum sol composition (1Ti(O-iPr)4: 0.009 F127: 0.13 HNO3: 1.3 H2O: 25 C2H5OH) and heat treatment conditions (calcination at 673 K; stepwise increase in the temperature) were determined to form a mesoporous coating with a specific surface area of 130 m2/g and an average pore diameter of 5.4 nm. It was found that the concentrations of metals (0.5–4 wt %), average particle sizes (1.0–3.5 nm), and particle size distributions in the Pt-Sn/TiO2 materials can be mainly regulated by varying the nature of the solvent, the concentration of Pt-Sn carbonyl complexes, and the time of adsorption, whereas the electronic state of metals can be fine-tuned by thermal treatment conditions. In an oxidizing atmosphere, the Pt-Sn carbonyl complexes decomposed with the formation of a two-phase system (Pt○ and SnO2). Thermal treatment in a vacuum and an inert or reducing atmosphere led to the formation of bimetallic phases (PtSn and Pt3Sn), whose stucture was regulated by the composition of a gas atmosphere and by the calcination temperature.