Methanol decomposition to synthesis gas at low temperature over palladium supported on ceria–zirconia solid solutions Original Research Article

The CexZr1−xO2 solid solution was used as a support of a palladium catalyst for methanol decomposition to synthesis gas at low temperature. All Pd-containing catalysts tested in this study showed high selectivity to synthesis gas (over 96%). The Pd supported on the composite oxide with a Ce/Zr molar ratio of 4/1 exhibited the highest activity. Pd/Ce0.8Zr0.2O2 (17 wt.%) (cop) (prepared by coprecipitation method) showed a conversion of 51.2% for the methanol decomposition at 473 K, which was higher than those over 17 wt.% Pd/CeO2 (cop) (40.7%) and 17 wt.% Pd/ZrO2 (cop) (24.3%) at 473 K. The 17 wt.% Pd/Ce0.8Zr0.2O2 (cop) catalyst showed a higher BET surface area and smaller Pd particles than those of 17 wt.% Pd/CeO2 (cop). Moreover, a more active Pdσ+ state could be maintained by Zr4+ ion modification due to promotion of the oxygen mobility and enhancement of the reductibility and increase in the acid sites of the CeO2 support. The 17 wt.% Pd/Ce0.8Zr0.2O2 (cop) catalyst showed a much higher conversion (51.2%) than that over 17 wt.% Pd/Ce0.8Zr0.2O2 (imp) (prepared by impregnation method) (17.2%) at 473 K. This is due to the 17 wt.% Pd/Ce0.8Zr0.2O2 (cop) possessing many small Pd particles. The 17 wt.% Pd/Ce0.8Zr0.2O2 (cop) catalyst showed an initial conversion of 51.2% at 473 K but the conversion decreased to 43.1% after 24 h on stream. This deactivation was attributed to carbonaceous deposit on the catalyst surface. The amounts of coke on the 17 wt.% Pd/Ce0.8Zr0.2O2 (cop) catalyst were 0.9 wt.% after 24 h on stream at 473 K and 2.1 wt.% after 1 h on stream at 523 K.