Catalytic behavior of Mo-Bi-Fe-Co-K-M-O(M=Ce,Gd,CeGd)catalysts for selective oxidation of isobutene

The further improvement of methacrolein(MAL)selectivity from isobutene(IB)oxidation is crucial and challenging.In this study,based on the typical Mo-Bi-Fe-Co-K-O mixed metal oxide,the rare earth element Gd-doped,Ce-doped and CeGd co-doped catalysts were prepared by co-precipitation strategy to increase the selectivity of MAL from 47.9%to 49.8%,64.2% and 68.6%,respectively.In order to elucidate in-depth the promoting effect of Ce and/or Gd,various characterizations were utilized including X-ray diffraction patterns(XRD),Raman,X-ray fluorescence spectrometry(XRF),X-ray photoelectron spectroscopy(XPS),O_(2)-temperature programmed desorption(O_(2)-TPD),H2-temperature programmed reduction(H2-TPR),CO_(2)-temperature programmed desorption(CO_(2)-TPD),IB-temperature programmed desorption(i-C4-TPD)and in-situ IB-Fourier transform infrared spectroscopy(IB-FTIR).Both Ce and Gd finely regulate the bulk and surface structure of the catalyst,thus altering the redox ability,oxygen mobility and storage ability and basicity.Compared with Ce,Gd addition slightly regulates the variation of Co^(2+)/Co^(3+)redox couples,greatly enhances the interaction among the components on the catalyst,thus only increases the content of surface oxygen species and has little effect on their mobility.While Cecontaining catalyst performs stronger oxygen storage and migration ability,thus leading to the overproduction of surface Odefectspecies,which are proposed to be the active sites for the production of MAL and COx.The CeGd co-doped catalyst possesses the proper content of surface Odefectspecies,thus exhibits much higher MAL selectivity.Moreover,the promoting mechanism of Ce and/or Gd over IB oxidation is proposed.Therefore,this work is helpful for understanding the influence of rare earth elements on the structure of mixed metal oxides and the olefin selective oxidation reaction.

Alloy strategy to synthesize Pt-early transition metal oxide interfacial catalysts

Metal oxide supported metal catalysts show promising catalytic performance in many industry-relevant reactions.However,the enhancement of performance is often limited by the insufficient metal/metal oxide interface.In this work,we demonstrate a general synthesis of Pt-early transition metal oxide(Pt-MO_(x),M=Ti,Zr,V,and Y)catalysts with rich interfacial sites,which is based on the air-induced surface segregation and oxidation of M in the supported Pt-M alloy catalysts.Systematic characterizations verify the dynamic structural response of Pt-M alloy catalysts to air and the formation of Pt-MO_(x) catalysts with abundant interfacial sites.The prepared Pt-TiO_(x) interfacial catalysts exhibit improved performance in hydrogenation reactions of benzaldehyde,nitrobenzene,styrene,and furfural,as a result of the heterolytic dissociation of H_(2) at Pt-metal oxide interfacial sites.

Tuning the local electronic structure of oxygen vacancies over copper-doped zinc oxide for efficient CO_(2) electroreduction

Oxygen vacancies in metal oxides can serve as electron trap centers to capture CO_(2) and lower energy barriers for the electrochemical CO_(2) reduction reaction(CO_(2)RR).Under aqueous electrolytes,however,such charge-enriched active sites can be occupied by adsorbed hydrogen(H∗)and lose their effectiveness for the CO_(2)RR.Here,we develop an efficient catalyst consisting of Cu-doped,defect-rich ZnO(Cu–ZnO)for the CO_(2)RR,which exhibits enhanced CO Faradaic efficiency and current density compared to pristine ZnO.The introduced Cu dopants simultaneously stabilize neighboring oxygen vacancies and modulate their local electronic structure,achieving inhibition of hydrogen evolution and acceleration of the CO_(2)RR.In a flow cell test,a current density of more than 45​mA​cm^(−2) and a CO Faradaic efficiency of>80%is obtained for a Cu–ZnO electrocatalyst in the wide potential range of−0.76​V to−1.06​V vs.Reversible Hydrogen Electrode(RHE).This work opens up great opportunities for dopant-modulated metal oxide catalysts for the CO_(2)RR.