Conversion of ethanol to higher alcohols on Ni/MxOy-Al2O3 (M=La, Ce, Zr, Mg and Ti) catalysts: Influence of support characteristics
A new series of alumina supported nickel (8% w/w) catalysts, modified with promoters, La2O3, CeO2, ZrO2, MgO and TiO2, highly active for the conversion of ethanol to butanol and higher alcohols, at 200°C-220°C, in batch mode, under autogenous pressure, has been investigated. XRD and XPS results indicate the presence of metallic Ni and Ni aluminate as the active phases. H2-TPR studies reveal that the introduction of promoters improves nickel dispersion, reducibility and moderates the metal-support interactions.TPD of ammonia and CO2 studies establish the strong influence of the promoter oxides on the strength and population of acidic and basic sites. Ethanol conversion at 200°C varies in a narrow range, 36-42%. CeO2 and MgO modified catalysts display maximum selectivity towards butanol (48%) and higher alcohols, (81% and 75%) in comparison with the catalyst based on pristine alumina (28.9% and 40.5%). While the selectivity for butanol and higher alcohols is governed by the basicity of the catalysts, both metal function and basicity are required to drive ethanol conversion. Moderation of acidity helps in minimizing the formation of ethylene and other gaseous products. Analysis of used catalyst indicates that the structural and active phase characteristics are retained during use.
Acidity; Basicity;Butanol; C4+ alcohols; Ethanol conversion; Heterogeneous catalysts; High Selectivity; Metal function; Nickel-alumina; Oxide promoters
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