Nickel nanocrystals on well-defined supports for the exploration of new heterogeneous catalysis

Abstract

Tuning reactivity of catalysts is of importance both in industries and academia, since it can bring up new catalytic processes and more efficient catalysts. Nickel has been studied for many catalysis due to its ability of hydrogen adsorption. However, there have been critical obstacles in nickel catalysts known to be inevitable. In this thesis, I study two heterogeneous catalysis with nickel nanocrystals in gas and liquid phases in order to explore new catalysis and overcome presented impediments. The first study is about nickel nanocrystals on single crystalline MgO for dry reforming of methane. Nickel has been studied as the alternative of precious metals, but it is known that nickel is vulnerable to carbon formation and sintering. I show nickel-molybdenum nanocrystals migrate to the unstable sites such as edge on single crystalline MgO by proper heating under reactive gas. This phenomenon leads to blocking unstable step edges of single crystalline MgO, making the catalyst exceptionally stable for 850 hours of continuous reaction without coking. In the second study, I explore nickel nanocrystals on porous carbon for direct coupling of nitrobenzene to azobenzene. Highly dispersed nickel nanoparticles on porous carbon was achieved by deposition-precipitation method and carbonization. The catalyst shows high selectivity to azobenzene because of high porosity and dispersity of nickel nanocrystals. It was also found out that the catalyst selectively navigates condensation route due to partially oxidized nickel surface, preventing it from making aniline.