高活性耐硫MoO_(3)改性NiO-Al_(2)O_(3)催化剂用于焦炉煤气甲烷化

Highly active and sulfur-tolerant MoO_(3)modified NiO-Al_(2)O_(3)catalysts for coke oven gas methanation

采用双水解共沉淀法结合浸渍法合成了系列的MoO_(3)改性的xMoO_(3)/Ni O-Al_(2)O_(3)催化剂(x%为MoO_(3)的质量分数),利用固定床装置对催化剂的甲烷化反应活性和耐硫性能进行评价,并对失活前后催化剂进行详细表征。结果表明,随着MoO_(3)含量的升高MoO_(3)改性后的催化剂甲烷化活性有所下降,但MoO_(3)的掺杂显著提升了催化剂的耐硫性能。催化剂低温甲烷化活性降低的原因在于MoO_(3)负载量的增加降低了催化剂的活性比表面积,但MoO_(3)的引入也为硫化物提供了一个竞争吸附位点,进而延缓了活性位点的硫中毒过程。当MoO_(3)负载量(质量分数)为12.5%时,12.5MoO_(3)/Ni O-Al_(2)O_(3)催化剂在143 mg·m^(-3)H_(2)S/H_(2)气氛下运行时间长达7 h,远高于其他催化剂。12.5MoO_(3)/Ni O-Al_(2)O_(3)催化剂吸收硫的量(质量分数)达到0.71%,是Ni O-Al_(2)O_(3)催化剂硫吸附量的1.48倍。XPS表征进一步发现12.5MoO_(3)/Ni O-Al_(2)O_(3)催化剂表面生成的Mo S2最多,这说明在此负载量下Mo优先吸附了更多的硫而保护了活性位点。此外,MoO_(3)负载量为12.5%时,MoO_(3)在催化剂表面接近单层分散阀值,当竞争吸附发生时,为硫化物提供更多的吸附位点。

A series of xMoO_(3)/NiO-Al_(2)O_(3)catalysts(x%represented the mass fraction of MoO_(3))were prepared by double hydrolytic co-precipitation method combined with impregnation method.The methanation reaction activity and sulfur resistance of catalysts were evaluated using a fixed-bed reactor,and the catalysts were characterized in detail fresh and after deactivation.The results showed that the low-temperature methanation activity of the catalyst decreased with the increase in MoO_(3)loading,whereas the sulfur resistance of the catalyst was significantly enhanced after MoO_(3)doping.The decrease in catalyst activity for low-temperature methanation was attributed to the fact that the increase in MoO_(3)loading reduced the active specific surface area of the catalyst,but the introduction of MoO_(3)also provided a competitive adsorption site for sulfide,which can delay sulfur poisoning at the active site.The xMoO_(3)/NiO‑Al_(2)O_(3)catalyst with 12.5%MoO_(3)loading(mass fraction)maintained the highest methanation activity for 7 h in the presence of 143 mg·m^(-3)H_(2)S/H_(2)(81.1%CO conversion,550℃).The sulfur chemisorption content of 12.5MoO_(3)/NiO‑Al_(2)O_(3)catalyst reaching 0.71%(mass fraction)was 1.48 times that of NiO‑Al_(2)O_(3)catalyst and further XPS also confirmed that the amount of MoS2 generated was the highest,which indicated that Mo preferentially adsorbs more sulfur and protects the active site.In addition,at a MoO_(3)loading of 12.5%,MoO_(3)on the surface of the catalyst reached the threshold of monolayer dispersion,which can provide more adsorption sites for sulfides when competitive adsorption occurs.