Mohamed MM, Ichikawa M
Faculty of Science, Chemistry Department, Benha University, Benha, Egypt
J Colloid Interface Sci. 2000 Dec 15;232(2):381-388. doi: 10.1006/jcis.2000.7176.
The surface species formed from the reaction of CO+H(2)O and CO+O(2) and decomposition of HCOOH on Au incorporated into H-mordenite zeolite have been studied by means of in situ FTIR spectroscopy. On H-mordenite, a bidentate formate species (2912, 1536, and 1390 cm(-1)) is produced upon exposure to the CO+H(2)O gas mixture at 323 K, as well as different carbonate-like species (1956, 1852, 1705, and 1360 cm(-1)). The latter species was extensively formed in a short time and was responsible for hindering the CO(2) adsorbed species. However, Au/H-mordenite presented different vibration modes of formate species with a high emphasis on the monodentate ones (2950, 2916, 2896, 1690, and 1340 cm(-1)). The HCOOH adsorption on Au/H-mordenite showed two bands at 1622 and 1590 cm(-1) of the nu(as)(OCO) species, suggesting the formation of two types of formate species. The decomposition rate of the formate species formed on Au moieties was faster than that formed on H-mordenite. This was consistent with the calculated activation energies of CO(2) formation that showed a lower value (40.1 kJ/mol) on the former sample than on the latter one (63.3 kJ/mol). A dehydrogenation mechanism is proposed (HCOOH-->H(2)+CO(2)) for the decomposition of HCOOH on the Au/H-mordenite catalyst. On the other hand, the Au/H-mordenite catalyst activated the CO oxidation reaction. This reaction proceeded mainly through the formation of carboxylate species at first, which tended to obviate with time, preferring the formate species. The latter species resulted from the interaction of CO with OH stretching of the zeolite assisted by the presence of gas phase O(2). The formate species is further decomposed with time to carbonate species. Copyright 2000 Academic Press.
通过原位傅里叶变换红外光谱法研究了负载于氢型丝光沸石中的金上由CO+H₂O、CO+O₂反应以及HCOOH分解所形成的表面物种。在氢型丝光沸石上，于323K下暴露于CO+H₂O气体混合物时会产生一种双齿甲酸盐物种（2912、1536和1390cm⁻¹），以及不同的类碳酸盐物种（1956、1852、1705和1360cm⁻¹）。后一种物种在短时间内大量形成，并导致阻碍CO₂吸附物种。然而，Au/氢型丝光沸石呈现出甲酸盐物种的不同振动模式，其中单齿甲酸盐物种（2950、2916、2896、1690和1340cm⁻¹）占主导。HCOOH在Au/氢型丝光沸石上的吸附在1622和1590cm⁻¹处显示出ν(as)(OCO)物种的两条谱带，表明形成了两种类型的甲酸盐物种。在金部分上形成的甲酸盐物种的分解速率比在氢型丝光沸石上形成的要快。这与计算得出的CO₂形成活化能一致，前者样品的值（40.1kJ/mol）低于后者（63.3kJ/mol）。提出了一种在Au/氢型丝光沸石催化剂上HCOOH分解的脱氢机理（HCOOH→H₂+CO₂）。另一方面，Au/氢型丝光沸石催化剂活化了CO氧化反应。该反应首先主要通过形成羧酸盐物种进行，随着时间推移羧酸盐物种趋于消除，而更倾向于甲酸盐物种。后一种物种是由CO与沸石的OH伸缩振动相互作用在气相O₂存在的辅助下产生的。甲酸盐物种随着时间进一步分解为碳酸盐物种。版权所有2000年学术出版社。
