Alkali-driven selectivity of products on carbon-supported Ni-based catalysts during the HDO of guaiacol
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Date
2024
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Abstract
The catalytic hydrodeoxygenation (HDO) of guaiacol as a representative bio-oil molecule was studied using a series of carbon-supported Ni-based catalysts. The promoter effect of alkali metals (Ca and Mg) on the catalytic activity and selectivity was verified. Catalysts were prepared by wetness incipient method and N2 gas adsorp tion/desorption isotherms, X-ray diffraction, reduction/desorption temperature-programed, and CO chemi sorption analysis were performed to characterize the catalysts. In terms of the initial reaction-rate catalysts with 1 wt% alkali-promotors showed an increase in the activity up to ca. 1.4 and 1.2 times higher on Ni-Ca(1 %)/AC and Ni-Mg(1 %)/AC, respectively, compared to Ni/AC catalyst. The increase to 5 wt% in alkali promotors slightly reduced the initial activity of Ni. However, the turn-over frequencies estimated showed higher values when alkali content is increased from 1 wt% to 5 wt%. These apparent contradictorial results suggest the formation of new actives sites along reaction, probably constituted by a mixture of oxides NiO-CaO and NiO-MgO. The selectivity of products showed remarkable changes due to the presence of alkali-promotors and a mechanism or reaction is proposed based on the kinetics of formation and evolution of products. Mg-promoted led to the formation of cyclohexane. On the contrary, Ca-promoted catalysts led the mechanism to representative benzene yields. This is remarkable result regarding the efficiency of a HDO biorefinery. In general, it can be concluded that Ni-based catalysts promoted with alkali metals are an economical alternative for the catalytic conversion of representa tive target molecules from a bio-oil feed.
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Keywords
Ni-based catalysts, Alkali-promotors, Guaiacol conversion, Selectivity Biorefinery