Abstract
The hydrogenation of CO2 to CH3OH is mostly performed by a catalyst consisting mainly of copper and zinc (Cu/ZnO/Al2O3). Here, Cu-Zn based catalysts are generated using surface organometallic chemistry (SOMC) starting from a material consisting of isolated ZnII surface sites dispersed on SiO2 – ZnII@SiO2. Grafting of [Cu(OtBu)]4 on the surface silanols available on ZnII@SiO2 followed by reduction at 500 °C under H2 generates CuZnx alloy nanoparticles with remaining ZnII sites according to X-ray absorption spectroscopy (XAS). This Cu-Zn/SiO2 material displays high catalytic activity and methanol selectivity, in particular at higher conversion compared to benchmark Cu/ZnO/Al2O3 and most other catalysts. In situ XAS shows that CuZnx alloy is partially converted into Cu(0) and Zn(II) under reaction conditions, while ex situ solid state nuclear magnetic resonance and infrared spectroscopic studies only indicate the presence of methoxy species and no formate intermediates are detected, in contrast to most Cu-based catalysts. The absence of formate species is consistent with the higher methanol selectivity as recently found for the related Cu-Ga/SiO2.
Highlights
The conversion of carbon dioxide (CO2) to value added products would allow the mitigation of CO2 emissions that are recognized as a major contributor to climate change [1,2]
A Cu-Zn based catalyst was generated by surface organometallic chemistry forming CuZnx alloy nanoparticles along with residual ZnII sites on SiO2
This material contrasts with the previously prepared Cu-Zr or Cu-Ti based systems were no reduction of ZrIV and TiIV occurred but display similar feature to reported Cu-Ga based systems, which consist of CuGax alloy in the assynthetized material
Summary
The conversion of carbon dioxide (CO2) to value added products would allow the mitigation of CO2 emissions that are recognized as a major contributor to climate change [1,2]. One strategy to mitigate the deleterious effect of CO2 emissions would be to convert it by hydrogenation to methanol (CH3OH), an important bulk chemical that can be used for the generation of energy, thereby forming a closed carbon-fuel-cycle, referred to as the ‘‘methanol economy” [3,4,5,6]. This entails the sustainable production of H2, the efficient capture of CO2 as well as the use of highly active and selective hydrogenation catalysts.
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