Modulated Ni Particle Size Of Mesoporous Ni/MgO Catalyst And Research On Its Catalytic Performance

The regulation of active component particle size exerts decisive role in designing and preparing desired catalyst for enhancing activity and stability of catalysts.A series of mesoporous MgO supported Ni catalysts（Ni_x/MgO）was prepared with various particle size（3.6-8.8 nm）.The catalysts were characterized by N₂ adsorption,H₂-TPR,XRD,XPS,and TEM.SR of pure butanol and a specific mixture（acetone-butanol-ethanol=3/6/1,mass ratio）assumed as a model of bio-butanol raw mixture have been researched,in order to study the particle size effect of active component.The results showed that the butanol conversion increased with the increase of Ni particle size.The volcano-like curves were observed when the H₂ yield and H₂selectivity were plotted as a function of the nickel particle size in butanol steam reforming（BSR）and acetone-butanol-ethanol steam reforming（ABESR）reactions.Prepared mesoporous Ni_0.12/MgO catalysts exhibited the highest catalytic performance in two model reaction systems.Surprisingly,the Ni particle size effects in BSR developed difference with counterpart in ABESR.Specifically,the catalytic performance of mesoporous Ni_0.20/MgO（Ni particle size is 8.83 nm）even outperform that of mesoporous Ni_0.08/MgO（Ni particle size is 4.87 nm）catalyst with respect to lower by-products selectivity and higher hydrogen yield in ABESR compared to BSR results.Considering the difference of catalytic performance of same catalysts in BSR and ABESR,this could be explained by the following facts.In the absence of Ni ensembles,acetone,butanol,and ethanol would compete for Ni active sites which were used to facilitate cleavage of chemical bonds.If acetone known as carbon precursor preferentially adsorbed on a limited number of Ni ensembles,which not only hindered butanol and ethanol molecules access to the active sites of the catalyst,but also easier formed carbon covering Ni active sites.As a consequence,the reactants and intermediates could be incompletely reformed over the active sites to desired gaseous products.In the present case,comparing the Ni particles size effect in two model catalytic reactions of BSR and ABESR,we came to a conclusion that the reactant molecules structure also played a crucial role in metal particle size effects.Combined with literature regarding SR of organics,on the basis of available data,a plausible reaction scheme for BSR is illustrated.