Role of the Cu-ZrO₂ Interfacial Sites for Conversion of Ethanol to Ethyl Acetate and Synthesis of Methanol from CO₂ and H₂

Abstract

Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the Cu and ZrO2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu0 and Zr4+, respectively. It was found that the formation of Cu-ZrO2 interfacial sites increased the turnover frequency by an order of magnitude in both the conversion of ethanol to ethyl acetate and the synthesis of methanol from CO2 and H2.

The Role of Copper in the Upgrading of Bioalcohols

“…A thorough study of the effect of addition of Zr sites to Cu/SiO 2 catalysts has been conducted by the Dumesic group …”

“…On the other hand the strong increase in butanone observed for ALD systems confirms the negative effect of the highly dispersed ZrO 2. In contrast, an experiment conducted with a physical mixture of Zr/SiO 2 +Cu/SiO 2 resulted into poor improvements in terms of selectivity (Table , entry 11) relative to Cu/SiO 2 , thus confirming the importance of the intimate contact between copper as already highlighted . Also in this case, STEM analysis of the Cu‐Zr/SiO 2 sample prepared by CSR shows that this technique leads to deposition of ZrO 2 onto Cu nanoparticle surfaces and to formation of some clusters near Cu nanoparticles.…”

“…At horough study of the effect of addition of Zr sites to Cu/ SiO 2 catalysts has been conducted by the Dumesic group. [56]-The authors studied two series of Cu/SiO 2 catalysts modified with different loading of ZrO x depositedb yt wo techniques, namely controlled surface reactions (CSRs)a nd atomicl ayer deposition (ALD). With this procedure they aimed at obtaining systemsw ith well-defined Cu-ZrO x interfacial sites and at elucidating their role in catalytic activity and selectivity.…”

Influences of particle size and crystallinity of highly loaded CuO/ZrO2 on CO2 hydrogenation to methanol

“…Catalytic hydrogenation of CO 2 to methanol is an attractive pathway as it is an important feedstock . So far, various catalysts for this reaction, such as Cu/ZrO 2 , Cu‐Ag/ZrO 2 , Cu/ZrO 2 /SiO 2 , Cu/ZnO/ZrO 2 , Cu/CeO 2 /TiO 2 , MnO x /m‐CoO x , InO 2 /ZrO 2 , Cu‐In/SiO 2 , Ni‐Ga/SiO 2 , ZnO/ZrO 2 , Pd/ZnO, Pd‐Cu/SiO 2 , and Cu/ZnO/Al 2 O 3 , have been proposed. Among them, the Cu/ZrO 2 catalyst would be a promising candidate because of its activity and selectivity for CO 2 hydrogenation to methanol (S. Tada et al, unpublished data) …”

“…In CO 2 hydrogenation to methanol (CO 2 + 3H 2 → CH 3 OH + H 2 O) by Cu/ZrO 2 catalyst, the interface of Cu‐ZrO 2 is considered the active site . In contrast, the metallic Cu surface is known as an active center for direct reduction of CO 2 to undesirable CO via reverse water gas shift reaction (CO 2 + H 2 → CO + H 2 O) .…”