CO2 hydrogenation for C2+ hydrocarbon synthesis over composite catalyst using surface modified HB zeolite

• CO2 hydrogenation was examined using composite catalyst comprised of Cu–Zn–Al oxide and HB zeolite.
• HB zeolite modified with 1,4-bis(hydroxydimethylsilyl) benzene was effective for the catalyst.
• The yield of C2+ hydrocarbons reached 12.6C-mol% under a pressure of 0.98 MPa.
• The modification changed HB zeolite from hydrophilic to hydrophobic.
• The hydrophobic surface suppressed the deactivation of the strong acidic site of HB zeolite.

Synthesis of C2+ hydrocarbons such as LPG (liquefied petroleum gas) from CO2 is expected to reduce CO2 emission by the consumption of fossil fuels. In this study, CO2 hydrogenation over composite catalysts comprised of Cu–Zn–Al oxide catalyst and HB zeolite was examined for the synthesis of C2+ hydrocarbons by the combination of methanol synthesis over Cu–Zn–Al oxide and concurrent conversion of methanol over HB zeolite. When a non-modified zeolite was used for the composite catalyst, the yield of C2+ hydrocarbons was poor (<0.5C-mol%), which was lower than that of oxygenated compounds (methanol and dimethyl ether). The strong acid sites of zeolite for the transformation of dimethyl ether to C2+ hydrocarbons were seriously deactivated. The employment of zeolites modified with 1,4-bis(hydroxydimethylsilyl) benzene remarkably improved the catalytic activity of the corresponding composite catalysts to produce C2+ hydrocarbons in yields of more than 7C-mol%. The best yield of C2+ hydrocarbons became approximately 12.6C-mol% under a pressure of 0.98 MPa. The disilane modification produced hydrophobic zeolites showing water contact angles more than 130°. The disilane compound was converted to some condensed aromatics during CO2 hydrogenation at 300 °C, and the hydrophobicity was maintained even after the reaction. The enhanced catalytic activity is caused by suppressing the deactivation of the strong acid sites of HB zeolite with the hydrophobic surface. This improved composite catalyst will promote the production of C2+ hydrocarbons from CO2 even under low pressure conditions.

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