Gold particle size effects in the gas-phase hydrogenation of m-dinitrobenzene over Au/TiO2

The effect of Au particle size, supported on TiO2, on the gas-phase hydrogenation of m-dinitrobenzene has been considered. The catalysts (Au loading = 0.1 and 1 mol%) were prepared by impregnation with HAuCl4 and a range of Au particle sizes (3.4–10.0 nm) was generated by temperature-programmed reduction over the interval 603 K ⩽ T ⩽ 1273 K. A thermal treatment of TiO2 at T ⩾ 873 K was required for the allotropic change from anatase to rutile but the presence of Au lowered the requisite temperature for complete transformation by up to 400 K. m-Dinitrobenzene hydrogenation exhibited a particle size sensitivity where higher specific rates were obtained with smaller Au particles, irrespective of the support composition (i.e. anatase:rutile ratio). The reaction over each Au/TiO2 catalyst generated m-phenylenediamine (reduction of both –NO2 groups) and/or m-nitroaniline (reduction of one –NO2 group). A parallel/consecutive kinetic model has been applied to quantify the catalytic selectivity where Au particles <5 nm favoured m-nitroaniline production. The dependence of hydrogenation performance on Au particle size is accounted for in terms of a modification to Au electronic character, which impacts on m-dinitrobenzene adsorption/activation.

m-Dinitrobenzene hydrogenation over Au/TiO2 (see TEM image) exhibited a particle size sensitivity delivering higher specific rates over smaller Au particle sizes (in the range 3.4–10.0 nm), irrespective of support anatase:rutile ratio; Au particles <5 nm favour partial – NO2 reduction to generate m-nitroaniline, a response that is linked to Au electronic character, which impacts on m-dinitrobenzene adsorption/activation.Figure optionsDownload high-quality image (89 K)Download as PowerPoint slide