Effect of the promotion of ceria on Pd/MgO catalyst for methanol synthesis

The hydrogenation of CO was carried out over Pd supported on MgO. The addition of various lanthanide oxides increased the activity of Pd/MgO to produce methanol. CeO2 exhibited the highest promoting effect at a temperature as low as of 250 degreesC and the optimum molar ratio of Ce/Pd was about unity. TPR experiment showed that CeO2 on MgO (without Pd) suffered less reduction with hydrogen compared with that supported on Al2O3. Thus, the former retained the Ce(TV) state almost completely under the reducing condition, which was ascertained by XAFS measurement. XAFS analysis also indicated that Pd in Pd/MgO suffered reduction extensively while that in Pd/CeO2/MgO partly retained the oxidized state owing to the reduction-resistant CeO2 on MgO. The results of CO adsorption XPS, XAFS, and TEM measurement revealed that addition of CeO2 increased the dispersion of Pd metal particles. It was concluded that the high active of the catalyst resulted from the combination of highly dispersed Pd metal and partly oxidized Pd component with a Pd-O bond.