Ethanol to higher hydrocarbons over Ni, Ga, Fe-modified ZSM-5: Effect of metal content

• Ni, Fe, Ga modified ZSM-5 catalysts were tested in the conversion of ethanol to higher hydrocarbons.
• A positive effect on C2 conversion with metal content smaller than 1 wt.%.
• Same product selectivity of metal modified ZSM-5 at same conversion.
• Site time yield of metal modified ZSM-5 decrease with increasing metal content.
• High metal loading lead to reduced acid site strength of zeolite.

The effect of metal content on catalyst properties was studied by comparing unmodified HZSM-5 and 0.5–7 wt.% Ga, Fe and Ni modified HZSM-5 in the ethanol conversion to hydrocarbons at 623 K by combining detailed catalyst characterization (XRD, TEM, N2 adsorption, H2-TPR and NH3-TPD) and catalytic testing. Low metal amounts (<1 wt.%) were found to have a positive effect on the production of light olefins, C2–C4 paraffins, aromatics and C5+ hydrocarbons. Increasing the amount of metal leads to a decreased production of these hydrocarbons, which is attributed to bulky metal clusters formation. These clusters decrease the accessibility of the acid sites due to pore blockage. For the first time, catalyst performance in ethanol conversion have been assessed at similar conditions, i.e. same conversion, showing that the selectivity towards the various product classes was not altered by the metal introduction. The site time yields of the metal modified HZSM-5 catalysts, based on the total concentration of accessible acid sites, exhibit a decreasing trend as function of metal content. This can be attributed to a lower acid strength of the accessible acid sites.

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