Szanyi János, Kwak Ja Hun
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Phys Chem Chem Phys. 2014 Aug 7;16(29):15117-25. doi: 10.1039/c4cp00616j.
The adsorption of CO2 and CO was investigated on a pure γ-Al2O3 support material that has been used in Pd and Ru catalysts for the reduction of CO2. The adsorption of CO2 resulted in the formation of carbonates, bicarbonates and linearly adsorbed CO2 species. The amount and the nature of the adsorbed species were dependent on the annealing temperature of the alumina support. On γ-Al2O3 annealed at 473 K mostly bicarbonates formed, while no adsorbed CO2 was seen on this highly hydroxylated surface. With increasing calcination temperature the amount of both surface carbonates and linearly adsorbed CO2 increased, but still the most abundant surface species were bicarbonates. Surface carbonates and adsorbed CO2 can readily be removed from the alumina surface, while bicarbonates are stable to elevated temperatures. The interaction of CO with γ-Al2O3 is much weaker than that of CO2. At room temperature CO adsorbs only on Lewis acid sites, and can be readily removed by evacuation. At 100 K CO can probe different defect sites on the alumina surface. Under no conditions we have observed the formation of any carbonates or bicarbonates upon the interaction of CO with the pure alumina support. In co-adsorption experiments CO competes for adsorption sites with the linearly adsorbed CO2 on the 773 K-annealed γ-Al2O3 surface, but it does not result in the desorption of CO2, rather in the increased production of weakly held carbonates. After the removal of adsorbed CO, CO2 moves back to its original adsorption sites, i.e., Lewis acidic Al(3+) centers. The exposure of a CO2-saturated γ-Al2O3 to H2O did not affect any of the adsorbed surface species. The findings of this study will be used to rationalize the results of our ongoing in situ and in operando studies on the reduction of CO2 on supported Pd and Ru catalysts.
研究了二氧化碳和一氧化碳在一种纯γ - 氧化铝载体材料上的吸附情况，该材料已用于钯和钌催化剂中二氧化碳的还原反应。二氧化碳的吸附导致形成碳酸盐、碳酸氢盐和线性吸附的二氧化碳物种。吸附物种的数量和性质取决于氧化铝载体的退火温度。在473K退火的γ - 氧化铝上，主要形成碳酸氢盐，而在这个高度羟基化的表面上未观察到吸附的二氧化碳。随着煅烧温度的升高，表面碳酸盐和线性吸附的二氧化碳的量都增加，但最丰富的表面物种仍然是碳酸氢盐。表面碳酸盐和吸附的二氧化碳可以很容易地从氧化铝表面去除，而碳酸氢盐对升高的温度稳定。一氧化碳与γ - 氧化铝的相互作用比二氧化碳弱得多。在室温下，一氧化碳仅吸附在路易斯酸位点上，并且可以通过抽空很容易地去除。在100K时，一氧化碳可以探测氧化铝表面的不同缺陷位点。在任何条件下，我们都未观察到一氧化碳与纯氧化铝载体相互作用时形成任何碳酸盐或碳酸氢盐。在共吸附实验中，一氧化碳在773K退火的γ - 氧化铝表面上与线性吸附的二氧化碳竞争吸附位点，但这不会导致二氧化碳的解吸，而是导致弱结合碳酸盐的产量增加。去除吸附的一氧化碳后，二氧化碳回到其原始吸附位点，即路易斯酸性的Al(3+)中心。将二氧化碳饱和的γ - 氧化铝暴露于水不会影响任何吸附的表面物种。本研究的结果将用于合理解释我们正在进行的关于负载型钯和钌催化剂上二氧化碳还原的原位和 operando 研究的结果。
