Polyacrylamide-assisted synthesis of highly dispersed Ni nanoparticles wrapped by SAPO-11 molecular sieves for enhanced alkane hydroisomerization performances

A novel polyacrylamide-assisted method for synthesizing the hierarchical SAPO-11-wrapped Ni catalyst was proposed. In this method, firstly, Ni 2+ ions from nickel salts were coordinated with nitrogen atoms in polyacrylamide (HPAM) to form a Ni 2+ -HPAM complex; then, Ni 2+ -HPAM was adsorbed on negative SAPO-11 crystals during the crystallization of SAPO-11, and Ni 2+ -HPAM was wrapped by SAPO-11 crystals with the growth of these crystals; finally, Ni 2+ -HPAM was transformed into NiO nanoparticles (about 2.5 nm) wrapped by SAPO-11 crystals after the HPAM was removed during calcination. This method obtained an in-situ Ni@SAPO-11 assembly with hierarchical pore structures and highly dispersed Ni metals. Compared with both Ni/SAPO-4.0 with the same Ni content synthesized by conventional impregnation and the Ni@SAC-4.0 in which Ni salt was introduced into SAPO-11 in situ without HPAM addition, the as-synthesized catalyst (Ni@SACH-4.0) exhibited a higher Ni dispersion with smaller Ni nanoparticles, and more mesopores and Brønsted (B) acid sites. Consequently, Ni@SACH-4.0 showed a higher C 10 isomer yield (78.2%) and a lower cracking selectivity (9.4%) than Ni/SAPO-4.0 and Ni@SAC-4.0.