Effect Of Preparation Conditions On Structure And Catalytic Performance Of Co-Mo/MgAl-LDO Sulfur-resistant Catalyst For Water-gas Shift Reaction

Hydrogen is an important green energy,and the most effective hydrogen generation process is water-gas shift（WGS）reaction.The raw materials of hydrogen generation are changing to bituminous or brown coal,heavy oil and residual oil with poor quality and high sulfur.The gasification of these raw materials is taken by all kinds of advanced pressurized gasification technologies,and the gasification gas contains high concentration of CO,water vapor,and sulfur content.Therefore,in order to obtain clean and high efficient hydrogen production,the key issue is to develop efficient sulfur resistance shift catalyst.In view of the poor low temperature activity of CoMo sulfur resistant shift catalyst,a series of CoMo sulfur resistant shift catalysts with good low temperature activity were prepared in this study by varying the nature of support,the content of active metal and additives.Meanwhile,the as-prepared samples were characterized by X-ray powder diffractometer（XRD）,N₂ physical adsorption at low temperature,temperature programmed reduction（H₂-TPR）,temperature programmed desorption（CO₂-TPD）,Laser Raman spectroscopy（Raman）,transmission electron microscopy（TEM）as well as WGS tests to study the the structure and catalytic performance of these catalysts.Firstly,we developed a novel Co-Mo sulfur-resistant shift catalyst using Mg-Al layered double oxide（MgAl-LDO）as support.MgAl-LDO with different Mg/Al molar ratios（Mg/Al=3～6）were prepared from Mg-Al layered double hydroxides by co-precipitation method.It was found that the catalytic activity of CoMo/MgAl-LDO increases with increasing the Mg/Al ratio from 2 to 5 and then decreases with further increasing the Mg/Al ratio,The highest activity was obtained on the CoMo/MgAl-LDO catalyst with the Mg/Al ratio equal to 5,which is much higher than that of a commercial CoMo/MgAl₂O₄ catalyst.The characterization results show that the catalytic activity is related to the sulfidation degree of active metal and the amount of sulfide phase.Secondly,according to that the brucite-like host layers consist of divalent and trivalent metal cations that can be changed not only in quantity but also in kinds,a series of Co（x）MgAl-LDO[x=n Co²⁺/(nCo²⁺+nMg²⁺),(nCo²⁺+nMg²⁺)/Al³⁺=5]supports were prepared from hydrotalcite-like compounds by co-precipitation method,and the influences of Co contend and addition method on the physicochemical properties and catalytic performance of Mo/Co（x）MgAl-LDO for WGS was investigated.The catalytic activity of sulfided Mo/Co（x）MgAl-LDO increases with increasing the Co content from 1%to 5%and then decreases with further increasing the Co content.The Mo/Co（5%）MgAl-LDO catalyst shows much higher activity than the CoMo/MgAl-LDO catalyst with the same metal content.The results showed that appropriate Co content could improve the dispersion of active phase MoS₂.Finally,the effect of Nb content on the physicochemical properties and catalytic performance of CoMo/Nb（x）MgAl-LDO for WGS was investigated.we developed a series of CoMo sulfur resistant shift catalyst by using Nb（x）MgAl mixed oxide[x=nNb²⁺/(nNb²⁺+nMg²⁺),(nNb²⁺+nMg²⁺)/nAl³⁺=5]as catalyst support,which is prepared from Nb-modified MgAl-hydrotalcite by co-precipitation method.The highest activity was obtained on the CoMo/Nb（5%）MgAl-LDO catalyst.It was found that adding the appropriate amount of acidic Nb oxide can significantly improve the catalytic activity at a low temperature.