Effect of cerium incorporation into zirconia on the activity ofCu/ZrO2 for methanol synthesis via CO hydrogenation

• Published in: Journal of catalysis Vol. 235
• Main Authors: Pokrovski, Konstantin A., Rhodes, Michael D., Bell, Alexis T.
• Format: Journal Article
• Language: English
• Published: United States 24.08.2005
• Subjects: 37; ATOMS; CALCINATION; CAPACITY; CATALYSTS; CATIONS; CERIUM; cerium zirconia Cu/ZrO2 methanol synthesishydrogenation; CRYSTAL STRUCTURE; FORMATES; HYDROGENATION; HYDROLYSIS; METHANOL; OXIDES; RAMAN SPECTROSCOPY; SOLID SOLUTIONS; SPECTROSCOPY; SYNTHESIS; X-RAY DIFFRACTION
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2005.09.002

The effects of Ce incorporation into ZrO2 on the catalyticperformance of Cu/ZrO2 for the hydrogenation of CO have beeninvestigated. A Ce0.3Zr0.7O2 solid solution was synthesized by forcedhydrolysis at low pH. After calcination at 873 K, XRD and Ramanspectroscopy characterization indicated that the Ce0.3Zr0.7O2 had a t''crystal structure. 1.2 wt percent Cu/Ce0.3Zr0.7O2 exhibited H2consumption peaks at low temperature (<473 K) during H2-TPRindicating a significant fraction (~; 70 percent) of Ce4+ is reduced toCe3+. 1.2 wt percent Cu/Ce0.3Zr0.7O2 is 2.7 times more active formethanol synthesis than 1.2 wt percent Cu/m-ZrO2 at 3.0 MPa attemperatures between 473 and 523 K and exhibits a higher selectivity tomethanol. In-situ infrared spectroscopy shows that, analogous toCu/m-ZrO2, the primary surface species on Cu/Ce0.3Zr0.7O2 during COhydrogenation are formate and methoxide species. A shift in the bandposition of the bridged methoxide species indicated that some of thesegroups were bonded to both Zr4+ and Ce3+ cations. For both catalysts, therate-limiting step for methanol synthesis is the reductive elimination ofmethoxide species. The higher rate of methanol synthesis onCu/Ce0.3Zr0.7O2 relative to Cu/m-ZrO2 was primarily due to a ~; 2.4 timeshigher apparent rate constant, kapp, for methoxide hydrogenation, whichis attributed to the higher surface concentration of H atoms on theformer catalyst. The increased capacity of the Ce-containing catalyst isattributed to interactions of H atoms with Ce-O pairs present at thesurface of the oxide phase.