Ni落位对正庚烷加氢异构-氢解竞争的调控作用OA

Using n-heptane(n-C7)as a model molecule,two types of Ni-based bifunctional catalysts,namely Ni-HZSM-22/Al2O3 and Ni-Al2O3/HZSM-22,featuring atomic-and nanoscale metal-acid proximity,respec-tively,were prepared to systematically investigate the effect of Ni placement on the competition between hydroi-somerization and hydrogenolysis.The results show that Ni placement simultaneously regulates the Ni‒support interaction,the surface chemical environment of Ni species,and the distribution of accessible Ni sites.Com-pared with those of Ni-HZSM-22/Al2O3,the Ni2+-related Ni 2p3/2 peaks of Ni-Al2O3/HZSM-22 shift markedly toward higher binding energies,indicating strong Ni-O-Al interactions between Ni and Al2O3.Meanwhile,the Al2O3-supported environment favors the maintenance of a relatively high proportion of accessible Ni sites at moderate-to-high Ni loadings.The n-C7 hydroisomerization results show that the i-C7 yields over both series of Ni-based bi-functional catalyst exhibits a volcano-type variation.At low Ni loadings,the reaction is limited by insufficient dehydrogenation/hydrogenation functionality of the Ni sites,whereas at high Ni loadings,enhanced Ni-mediated hydrogenolysis decreases the isomerization selectivity.Among the catalysts,2.0Ni-Al2O3/HZSM-22 achieves the highest isomer yield of 57.19％.Moreover,the trend in isobutance(i-C4)formation over this catalyst is similar to that over the Pt reference catalyst,while its CH4 yield is relatively low.These findings indi-cate that the Al2O3-supported Ni sites can effectively supress Ni-mediated C-C bond hydrogenolysis while main-taining the required dehydrogenation-hydrogenation functionality.The key to designing Ni-based bifunctional hydroisomerization catalysts is therefore to achieve an appropriate balance between the metal and acid functions while suppressing the hydrogenolysis activity of the Ni sites,rather than simply optimizing metal-acid proximity or metal loading.