The role of nanosized nickel particles in microwave-assisted dry reforming of lignin

Abstract

Dry reforming (DR) of lignin with supported Ni nanoparticles under microwave irradiation (MWI) with plasma generation has been studied. Nickel depositing on the lignin surface was carried out by two different procedures. According to the first procedure, Ni was deposited from an aqueous solution of nickel acetate by impregnation. The second procedure included depositing a colloid solution of nickel particles in toluene preliminary obtained by metal vapor synthesis (MVS). As a result in both cases Ni particles of 6nm size were formed on the lignin surface. Both types of nanocatalysts govern the microwave (MW)-assisted DR of lignin. MW treatment of the mechanical mixture of a carbon sorbent with a high dielectric loss factor, and a Ni-containing lignin sample obtained by the first method resulted in the 65wt.% lignin conversion to synthesis gas with the H2/CO ratio of ∼1/1. The content of syngas in the products was 8090wt.%. It was found that MW treatment sharply increases the yield of syngas in the reforming as compared with the convective heating. The Ni-containing lignin samples before and after reforming were investigated by XRD, TEM, EDA, and magnetic measurements. It was established that different depositing procedures lead to the formation of X-ray amorphous Ni particles with markedly different magnetic properties. In contrast to entirely paramagnetic sample obtained from nickel acetate solution, superparamagnetic Ni0 particles formed by MVS exhibited a high capacity for absorption of MWI, sufficient for plasma to be generated and the reforming temperature to be reached without an additional sorbent.