Effect of carbonization temperature on the nickel crystallite size of a Ni/C catalyst for catalytic hydrothermal gasification of organic compounds

Abstract

A carbon based nickel (Ni) catalyst was prepared by ion exchanging Ni ions with the ion exchangeable sites in an ion exchange resin followed by carbonization of the resin. Effect of carbonization parameters such as temperature and time on nickel crystallite size and dispersion were studied. Samples were prepared at 500, 600, 700 and 800 °C to investigate the effect of carbonization temperature. The XRD pattern and TEM images of the catalysts showed that Ni particles become bigger in size as carbonization temperature increases. No effect of carbonization time on particle size was observed. The catalytic hydrothermal gasification (CHTG) experiments with 0.2% TOC organic water at 350 °C, 20 MPa, and 50 h −1 liquid hourly space velocity (LHSV) showed that the conversion or activity decreased as particle size increased, from 99% for Ni500 (3.3 nm) to 25% for Ni800 (21.5 nm). The extended time experiments showed that the conversion or activity was stable for both Ni500 and Ni700 for 50 h run time. The XRD and TEM patterns of the two catalysts after 50 h gasification run showed that Ni500 with smaller particle size shows slightly higher sintering rate than Ni700 with bigger particles.