硫化NiW/Al2O3上H2同时催化还原SO2和NO的反应机理

研究了硫化NiW/Al2O3催化剂上的NO分解反应、H2还原NO反应以及H2同时还原NO和SO2反应.在活性评价及XRD和XPS表征的基础上提出了H2同时催化还原SO2和NO的反应机理.结果表明,NO在硫化催化剂上可以完全分解,但由于催化剂晶格硫遭到严重氧化,因此还伴随着SO2的生成.该氧化作用导致了催化剂中晶格硫的大量流失和催化剂的失活;在NO反应体系中引入等摩尔的H2后,晶格硫的流失速度减缓,流失程度得到一定抑制.这是因为H2能与晶格硫竞争消耗NO解离出的Oad,此外,被氧化的晶格硫一部分还可进一步被还原,返回到催化剂晶格;在SO2和NO同时还原体系中,550℃时,SO2和NO的转化率都可达到100%,单质硫产率超过90%.稳定性测试表明,10 h后催化剂仍能保持高活性,没有发生失活.这主要是因为反应气中的SO2能够被H2还原为元素硫物种,从而可以对晶格硫进行源源不断的补充.

The Mechanism for Simultaneous Reduction of SO2 and NO over sulfided NiW/Al2O3 Catalyst

The decomposition of NO, the reduction of NO and the simultaneous reduction of NO and SO2 by H2 over sulfided NiW/Al2O3 were investigated, respectively. The mechanism of the simultaneous reduction of SO2 and NO by H2 was proposed based on the activity tests of catalyst and its characterization of XRD and XPS. The experimental results showed that NO was decomposed completely over sulfided catalyst accompanied with the formation of SO2, which resulted from the oxidation of lattice sulfur. This oxidation of lattice sulfur led to the loss of lattice sulfur and the deactivation of catalyst. After the addition of equivalent H2 to NO stream, the loss rate of lattice sulfur was slowed down and the loss degree was abated due to the competitive consumption of Oad by H2 and lattice sulfur as well as the reduction of part oxidized lattice sulfur and return to lattice. In the system of simultaneous reduction of SO2 and NO, the conversions of both SO2 and NO approached nearly 100 % and the yield of sulfur was over 90 % at 550 ℃. The stability test at 550 ℃ shows that the catalyst still maintained high activity after 10 h and no deactivation was observed, which was principally owing to the continuous reduction of SO2 in feeding gas by H2 to elemental sulfur species to replenish lattice sulfur.