A Highly Stable Copper‐Based Catalyst for Clarifying the Catalytic Roles of Cu⁰ and Cu⁺ Species in Methanol Dehydrogenation

Abstract

Identification of the active copper species,a nd further illustration of the catalytic mechanism of Cu-based catalysts is still ac hallenge because of the mobility and evolution of Cu 0 and Cu + species in the reaction process.Thus, an unprecedentedly stable Cu-based catalyst was prepared by uniformly embedding Cu nanoparticles in amesoporous silica shell allowing clarification of the catalytic roles of Cu 0 and Cu + in the dehydrogenation of methanol to methyl formate by combining isotope-labeling experiment, in situ spectroscopy, and DFT calculations.I ti ss hown that Cu 0 sites promote the cleavage of the OÀHbond in methanol and of the CÀHbond in the reaction intermediates CH 3 Oa nd H 2 COOCH 3 which is formed from CH 3 Oand HCHO,whereas Cu + sites cause rapid decomposition of formaldehyde generated on the Cu 0 sites into

Preserving the Active Cu–ZnO Interface for Selective Hydrogenation of CO2 to Dimethyl Ether and Methanol

“…As shown in Figure C,D, the disappearance of the shake-up Cu 2+ satellite peak located at 937–948 eV and the simultaneous shift of the Cu 2p 3/2 peak toward lower BEs in all of the reduced catalysts indicated the reduction of Cu 2+ to Cu 0 or Cu + . ,,, The Cu LMM XAES spectra were performed to distinguish Cu + and Cu 0 species (Figure S13, SI). For the reduced CZA, the peaks at 918.1 and 916.0 eV were attributed to Cu 0 and Cu + species, respectively. ,,, While for the CZAS@SA catalysts, the peaks for Cu 0 and Cu + species appeared at about 918.5 and 914.3 eV, respectively, in good agreement with our previous study . Interestingly, the Zn 2p 3/2 peak in the reduced CZA catalyst was at about 1022.4 eV, which was much higher than that in calcined CZA (1020.0 eV) (Figure B,D).…”

“…42,43,45,46 While for the CZAS@SA catalysts, the peaks for Cu 0 and Cu + species appeared at about 918.5 and 914.3 eV, respectively, in good agreement with our previous study. 39 Interestingly, the Zn 2p 3/2 peak in the reduced CZA catalyst was at about 1022.4 eV, which was much higher than that in calcined CZA (1020.0 eV) (Figure 2B,D). This higher BE value did not result from the reduction of ZnO into metallic Zn (Zn 0 ) because of the comparable Zn 2p 3/2 peak positions for Zn 0 and ZnO (at 1021.4 and 1021.7 eV, respectively 50 ).…”

“…The oxidation of Cu 0 to Cu + originated from the adsorption of the CH 3 O reaction intermediate on Cu 0 sites via its oxygen (O) atom, while the reduction of Cu + to Cu 0 resulted from the consumption of CH 3 O species during the reaction. 39 CO 2 itself has O atoms, and many other Ocontaining reaction intermediates will be formed during CO 2 hydrogenation to CH 3 OH. The Cu 0 sites were oxidized into the Cu + sites when CO 2 and these reaction intermediates were adsorbed on Cu 0 sites via their O atoms, and the Cu 0 sites were recovered/reduced with the removal of these reaction species by purging the stream of Ar.…”

“…In such a case, the release of Cu atoms from the spinel matrix can be smoothed under the working conditions, leading to the slowdown in the agglomeration rate of Cu. , However, it remains a big challenge for this method to release both Cu and metal/metal oxide atoms at the same time. Recently, the development of core–shell structured metal nanocatalysts have attracted considerable attention. − Numerous experimental observations showed that the confinement of the shell stabilized the metal NPs more efficiently than the metal–support interactions, while the tunable porosity of the shell ensured the accessibility of reactant molecules to the metal NPs. − We found that the Cu NPs that were well confined in the ordered mesoporous SiO 2 shell possessed high thermal stability even at a high temperature of 550 °C. , …”

“…35−39 We found that the Cu NPs that were well confined in the ordered mesoporous SiO 2 shell possessed high thermal stability even at a high temperature of 550 °C. 39,40 While many efforts have been devoted to developing the preparation methods to stabilize Cu itself, less attention has been paid to exploring the preparation strategies to stabilize the active Cu−metal (oxide) interface. Yang et al developed a hydrothermal synthesis method to encapsulate Cu/ZnO/ Al 2 O 3 of a millimeter size in the zeolite shell (HZSM-5 and Silicalite-1) with a micrometer thickness (3.9−5.0 μm) for direct conversion of syngas to DME.…”