Novel functions of composite catalysts derived from Pd and support metal oxides-mechanism and utilization

Pd/ZnO在不同负载Pd催化剂中对甲醇的蒸汽重整和脱氢制HCOOCH_3表现出异常高的催化性能。水蒸气重整和脱氢制HCOOCH_3的选择性分别达到99.5%和80%。其他负载型钯催化剂的水蒸气重整和HCOOCH_3脱氢选择性分别为0 ~ 40%和0%。通过在较高的温度下还原催化剂，Pd/ZnO对蒸汽重整和脱氢的催化性能得到了很大的提高。催化性能的提高是由于催化剂在之前的还原过程中形成了PdZn合金。XP谱分析表明，在PdZn合金的形成过程中，Pd向Zn发生了电子转移。在合金催化剂上，反应中生成的甲醛被- oh或ch3o -有效地攻击，转化为CO_2和H_…More 2或HCOOCH_3。在蒸汽重整和甲醇脱氢反应中，甲醛选择性地分解为CO和H_2。结果表明，在PdZn合金上的反应中，甲醛以eta^1 (O) -形式稳定在带正电荷的Pd位点上，并受到- oh或CH_3O-的亲核加成。在Pd产生新催化功能机理的基础上，开发了新型Pd_<3.1>Zn_<6.9>和PtZn合金催化剂。这些合金对甲醇脱氢制HCOOCH_3和蒸汽重整具有较高的选择性。对不同制备方法制备的Pd/ZnO催化剂进行了实验研究。用Na_2CO_3溶液沉淀Pd （II）和Zn （II）得到的Pd/ZnO （10wt% Pd）是目前研究的Pd催化剂中蒸汽转化性能最好的。Pd/ZnO的活性是Cu/SiO_2 （30wt% Cu）的2倍。少

Pd/ZnO exhibited anomalously high catalytic performance for the steam reforming of methanol and the dehydrogenation to HCOOCH_3 among various supported Pd ctalysts. The selectivities for the steam reforming and the dehydrogenation to HCOOCH_3 were achieved at 99.5% and 80%, respectively. In contraast, the other supported Pd catalysts showed the selectivities of 0-40% and 0%, respectively for the steam reforming and the dehydrogenation to HCOOCH_3. The catalytic performance of Pd/ZnO for the steam reforming and the dehydrogenation was greatly improved by previously reducing the catalyst at higher temperatures. The increased catalytic performace was attributed to PdZn alloys formed in the previous reduction of the catalyst. By XP spectroscopy, it was revealed that electron transfer took place from Pd to Zn in the formation of PdZn alloys. Over the alloyed catalysts, formaldehyde species formed in the reactions were effectively attacked by -OH or CH_3O-, being transformed into CO_2 and H_ … More 2 or HCOOCH_3. Over the other catalysts containing unalloyed Pd, the formaldehyde species decomposed selectively to CO and H_2 in the steam steam reforming and the dehydrogenation of methanol. It was suggested that formaldehyde species were stabilized on positively charged Pd sites in eta^1 (O) -form in the reactions over PdZn alloys, and subjected to the nucleophilic addition of -OH or CH_3O-. On the basis of the proposed mechanism of the generation of new catalytic function of Pd, novel Pd_<3.1>Zn_<6.9> and PtZn alloy catalysts were developed. These alloys showed high selectivity for the dehydrogenation of methanol to HCOOCH_3 as well as the steam reeforming. Experimemts were carried out over Pd/ZnO catalysts prepared by various preparation methods. Pd/ZnO (10wt% Pd) obtained by precipitation of Pd (II) and Zn (II) with a Na_2CO_3 solution exhibited best performance for the steam reforming among the Pd catalysts so far studied. The activity of Pd/ZnO was twice that for Cu/SiO_2 (30wt% Cu) previously studied. Less