A Comparative Study of NiO/Al2O3 Catalysts Prepared by Different Combustion Techniques for Octanal Hydrogenation
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Four catalysts with the molar ratio of Ni:Al (1:2) were prepared by solution combustion synthesis (SCS) and sol–gel auto combustion synthesis (SGCS) techniques. Two fuels [urea and oxalyldihydrazide (ODH)] with distinct oxygen/carbon (O/C) ratios and chelating capability were chosen for investigating the effect of the fuel on the syntheses of these catalysts. All catalysts were fully characterized by PXRD, ICP-OES, TEM, H2-TPR, pyridine IR, H2-chemisorption and nitrogen physisorption. Pure NiO/Al2O3 (free of spinel) was achieved by application of SGCS and urea as a fuel. Thus, catalysts prepared by urea as a fuel showed high activity for hydrogenation of octanal even under moderate conditions (110 °C). Optimisation showed that the catalyst prepared via SCS using ODH as a fuel gave the best comparative aldehyde conversion and alcohol selectivity (98 and 97 %, respectively) albeit at a higher temperature of 150 °C. The catalysts with NiAl2O4 as the dominant phase presented the lowest acidity, likely due to the non-availability of acidic sites of alumina via formation of the spinel, thus making these catalysts highly selective and also offering a slow release of fresh Ni sites.
KeywordsNiO/Al2O3 NiAl2O4 Solution combustion Sol–gel auto combustion Hydrogenation
We thank SASOL, the National Research Foundation, South Africa (NRF) and the Technology and Human Resources for Industry Programme (THRIP Grant TP1208035643) for their financial support. We also thank the Electron Microscopy Unit at the University of KwaZulu-Natal (Westville).
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