Fabrication of subnanometric Ni clusters over the Ni/SAPO-11 hydroisomerization catalyst

The preparation of subnanometric non-noble metal catalyst remains difficult especially when the metal loading is more than 1 wt%. Herein, the subnanometric nickel clusters (0.87 nm) were fabricated over the Ni/SAPO-11 catalyst for n-hexane hydroisomerization with Ni loading of 1.8 wt%. They exhibit 3.4 times the content of Ni atoms on corner and step sites than nanoparticles. These special Ni atoms with rich dangling bonds and high surface energy exhibit enhanced ability in activation and breakage of the C-H in n-hexane and H-H bonds in H₂. DFT (density functional theory) results confirm that the activation energy for n-hexane dehydrogenation over Ni atoms on corner or step sites is only 10 and 60% of the one on terrace sites. The projected d-electron density states calculations reveal that the molecular-like electronic state of the nickel clusters are further strengthened when reducing the size to subnanometric level. It leads to the upshifting of the d-band center, which favors the activation of C-H and H-H bonds. All of these geometric and electronic effects generated by the subnanometric Ni clusters endow the Ni/SAPO-11 catalyst 2.3 times the rate of i-C₆ generation and nearly 2.8 times the turnover frequency (TOF) of nanoparticle counterpart.