Catalytic activity of mono- and bimetallic Ni based catalysts supported on Ce-M (M=Sm,Gd) mixed oxides for hydrogen production

Monometallic Ni/doped-ceria and bimetallic NiRe/doped-ceria supported catalysts were evaluated by water gas shift (WGS) reaction. The effect of support preparation methods and rare earth metals addition were investigated. A sol-gel, and combustion methods were used for the preparation of doped ceria (rare earth metals : Sm, Gd) supports and then Ni was added onto supports by impregnation method. Moreover, the influence of Re on WGS activity was investigated. It was found that an addition of rare earth metal into Ni/CeO2 enhances the surface area and assists Ni dispersion on ceria surface. Furthermore, the presence of rare earth metal reduces the crystallite size of CeO2 and increases the reducibility of Ni species at the surface. An increase of metallic Ni surface area and the Ni dispersion facilitate the CO adsorption on ceria surface. Furthermore, an addition of Re into 5%Ni/CeO2 leads to an improvement of WGS activity. The 1%Re4%Ni/Ce-5%Sm-O prepared by combustion method exhibits the highest CO conversion at 97%. From XANES results, it shows that Sm and Re donate electron to ceria, hence leading to a decrease in Ce oxidation state. An existence of Ce3+ generates greater oxygen vacancies and facilitates the Ce3+/Ce4+ redox cycle at ceria surface which results in enhancing the WGS catalytic performance.

本研究通过水煤气变换（Water Gas Shift, WGS）反应，对单金属镍/掺杂氧化铈负载型催化剂与双金属镍铼/掺杂氧化铈负载型催化剂的性能进行了评价。考察了载体制备方法与稀土金属掺杂对催化剂性能的影响：掺杂氧化铈载体的制备采用溶胶-凝胶法与燃烧法，所掺杂的稀土金属为钐（Sm）、钆（Gd），随后通过浸渍法将镍负载至载体表面；此外还探究了铼（Re）的添加对水煤气变换反应活性的影响。研究发现，在镍/氧化铈催化剂中掺杂稀土金属，可提升载体比表面积并促进镍在氧化铈表面的分散；同时，稀土金属的掺杂可减小氧化铈的晶粒尺寸，并提升表面镍物种的还原性能。金属镍比表面积的提升与镍分散性的改善，可促进一氧化碳（Carbon Monoxide, CO）在氧化铈表面的吸附。此外，在5%镍/氧化铈催化剂中添加铼，可进一步提升其水煤气变换反应活性。通过燃烧法制备的1%Re4%Ni/Ce-5%Sm-O催化剂，其一氧化碳转化率最高可达97%。X射线吸收近边结构（X-ray Absorption Near Edge Structure, XANES）测试结果表明，钐与铼会向氧化铈转移电子，从而降低铈的氧化态；三价铈（Ce³+）的存在可产生更多氧空位，并促进氧化铈表面的Ce³+/Ce⁴+氧化还原循环，进而提升水煤气变换反应的催化性能。