Structure and Catalytic Activity of Cr-Doped BaTiO3 Nanocatalysts Synthesized by Conventional Oxalate and Microwave Assisted Hydrothermal Methods.

Abstract

In the present study synthesis of BaTi1-xCrxO3 nanocatalysts (x = 0.0 ≤ x ≤ 0.05) by conventional oxalate and microwave assisted hydrothermal synthesis methods was carried out to investigate the effect of synthesis methods on the physicochemical and catalytic properties of nanocatalysts. These catalysts were thoroughly characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 physisortion, and total acidity by pyridine adsorption method. Their catalytic performance was evaluated for the reduction of nitrobenzene using hydrazine hydrate as the hydrogen source. Structural parameters refined by Rietveld analysis using XRD powder data indicate that BaTi1-xCrxO3 conventional catalysts were crystallized in the tetragonal BaTiO3 structure with space group P4mm, and microwave catalysts crystallized in pure cubic BaTiO3 structure with space group Pm3̅m. TEM analysis of the catalysts reveal spherical morphology of the particles, and these are uniformly dispersed in microwave catalysts whereas agglomeration of the particles was observed in conventional catalysts. Particle size of the microwave catalysts is found to be 20-35 nm compared to conventional catalysts (30-48 nm). XPS studies reveal that Cr is present in the 3+ and 6+ mixed valence state in all the catalysts. Microwave synthesized catalysts showed a 4-10-fold increase in surface area and pore volume compared to conventional catalysts. Acidity of the BaTiO3 catalysts improved with Cr dopant in the catalysts, and this could be due to an increase in the number of Lewis acid sites with an increase in Cr content of all the catalysts. Catalytic reduction of nitrobenzene to aniline studies reveals that BaTiO3 synthesized by microwave is very active and showed 99.3% nitrobenzene conversion with 98.2% aniline yield. The presence of Cr in the catalysts facilitates a faster reduction reaction in all the catalysts, and its effect is particularly notable in conventional synthesized catalysts.