Fe2O3添加对钛基SCR催化剂表面硫酸氢铵分解行为的影响规律

采用共沉淀法合成了TiO_2及TiO_2-Fe_2O_3载体,并对硫酸氢铵与上述载体之间的相互作用及硫酸氢铵的具体分解行为进行了研究.结果表明,催化剂载体表面含硫官能团主要以双齿硫酸盐的形式存在,含氮官能团以铵根离子的形式存在.当硫酸氢铵沉积于催化剂载体表面时,由于硫酸根离子具有较强的电负性,Ti原子及Fe原子处于电子缺失状态.对于TiO_2载体,硫酸根离子主要与Ti原子相连;而对于TiO_2-Fe_2O_3载体,Ti原子及Fe原子均为硫酸根离子主要的附着位点.采用热分析方法及原位红外对硫酸氢铵在TiO_2及TiO_2-Fe_2O_3载体表面的分解行为进行了研究,发现铁氧化物的添加显著促进了硫酸氢铵在低温区间内的分解行为;与铵根离子相比,硫酸根离子具有更高的热稳定性.催化剂稳定性测试结果表明,铁氧化物的添加显著提高了低温抗硫抗水性能,为实现低温SCR技术的工业应用提供了理论基础.

Investigation of the effect of Fe2O3 addition on the decomposition behavior of NH4HSO4 on the TiO2-based SCR catalyst surfaces

In this study, TiO₂ and TiO₂-Fe₂O₃ supports used for the selective catalytic reduction of NO with NH₃ were synthesized using the co-precipitation method. The interactions between NH₄HSO₄ and these supports, together with the detailed decomposition behavior of NH₄HSO₄ on the series catalyst supports, were investigated. On the catalyst support surfaces, sulfate species existed as bidentate SO₄^2- and N-containing functional groups were presented in the form of NH₄⁺. Given that NH₄HSO₄ was deposited on the catalyst surfaces, Ti and Fe atoms were present in an electron-deficit state because of the stronger electronegativity of SO₄^2-. In the case of TiO₂ support, Ti atoms functioned as a reservoir for the accommodation of sulfate anions. While for TiO₂-Fe₂O₃ mixed support, both Ti and Fe atoms sometimes interacted with sulfate species. Compared with NH₄HSO₄ deposited on the Ti support surface, the decomposition behavior of NH₄HSO₄ was promoted through adding Fe₂O₃. In situ DRIFTS results demonstrated that SO₄^2- possessed a higher thermal stability than NH₄⁺. Finally, the deactivation of catalysts by SO₂ and H₂O could be impeded in a certain extent by introducing Fe₂O₃, suggesting that Fe₂O₃-modified catalysts would be typically used in the low-temperature SCR systems in the future.