Promoted Synergic Catalysis between Metal Ni and Acid-Base Sites toward Oxidant-Free Dehydrogenation of Alcohols

In a number of heterogeneous catalysis processes, synergic catalysis of metal and acid-base sites of supports is of vital importance and remains a challenge to obtain largely improved catalytic performance. Herein, an acid-base-promoted Ni nanocatalyst supported on Ni/Al mixed metal oxide (denoted as Ni/NiAl-MMO) was prepared on the basis of the in situ structural topotactic transformation of NiAl-layered double hydroxide (NiAl-LDH) precursor. In situ studies including XRD, Raman, and EXAFS verify that the cubic NiO-like phase (Al3+-doped NiO species), with medium-strong acid-base sites (Ni delta+-O delta- pair), are well-distributed in the amorphous Al2O3 to form NiAl-MMO support. The concentration of Ni active site and acid-base sites can be simultaneously enhanced by precisely tuning the in situ structural topotactic transformation parameters of LDH precursor as revealed by CO pulse chemisorption, CO2-TPD, and NH3-TPD, so as to achieve a promoted synergic catalysis between metal Ni and acid-base sites. The resulting Ni/NiAl-MMO(400) shows largely enhanced catalytic performance (formation rate of 2-octanone: 78.5 mmol g(-1) h(-1)) toward oxidant-free dehydrogenation of 2-octanol to 2-octanone, which is 3.9 times larger than the conventional Ni/Al2O3 catalyst (formation rate of 2-octanone: 20.1 mmol g(-1) h(-1)). Studies on the structure-property correlation based on operando time-resolved EXAFS spectra and kinetic isotope effect (KIE) measurements reveal that such an excellent catalytic performance is attributed to the optimized synergic catalysis between Ni0 and medium-strong acid-base sites of support, which accelerates the bond cleavage of kinetically key steps: alpha-C-H and O-H, respectively.