Insight into deactivation of the carbon-/sintering-resistant Ni@Silicalite-1 for catalytic partial oxidation of methane to syngas

Ni-based catalysts show good activity and selectivity for the catalytic partial oxidation of methane (CPOM) to syngas, but still suffer from carbon deposition and Ni-sintering. Herein, Ni nanoparticles of 3-7 nm are successfully embedded inside the crystal of silicalite-1 (S-1) zeolite via one-pot hydrothermal synthesis. The Ni@S-1 catalysts, with high activity/selectivity, show high carbon-/sintering-resistance but still deactivates fast. The surface of Ni nanoparticles involved in the reaction is oxidized to form intermediate NiO species, which may react with the circumambient SiO2 (from S-1) in the presence of water vapor (by-product and/or intermediate-product of CPOM reaction) to form a dense Ni-3(Si2O5)(2)(OH)(2) layer around Ni nanoparticles. The formed Ni-3(Si2O5)(2)(OH)(2) compounds are hard to be reduced (even in H-2 at 800 degrees C; thus losing capacity to involve catalytic reaction cycle) while completely blocking the Ni-0 sites from contacting with reactants, which is the main cause for the Ni@S-1 deactivation. Not surprisingly, such deactivation problem can be solved easily by replacing Ni with highly anti-oxidative metals such as Rh.

Automated summary

Ni-based catalysts with Ni nanoparticles embedded in S-1 zeolite show high activity/selectivity and resistance to carbon deposition and Ni-sintering. However, they still suffer from deactivation due to the formation of a dense Ni-3(Si2O5)(2)(OH)(2) layer that blocks the contact between Ni and reactants.