Rational Design of the Heterogeneous Catalysts and Their Opportunities in Renewable Fuels

Abstract:

A sustainable economy requires the development of alternative energy to replace the energy based on fossil fuels, thus the hydrogen production and the biomass conversion attract a lot of research attentions recently to make the world sustainable.  The objective of the research is to develop novel catalysts and processes for the hydrogen production and the upgrading biomass-derived oxygenated compounds to useful chemicals and fuels.  The nanoparticle impregnation method was developed to prepare supported nanopartilce (np) catalysts with controlled particle sizes and composition.  And these np catalysts were applied for the non-oxidative dehydrogenation of methane for the production of CO_x-free hydrogen and sequestering carbon as potentially value-added by-product carbon nanotubes (CNTs).  Monosized Fe_0.65Ni_0.35 oxide nanoparticles with an average particle size of 9 nm were prepared by thermal decomposition of an Fe, Ni oleate-surfactant complex in octadecene under reflux; these nanoparticles were dispersed onto a Mg(Al)O support to form a Fe-Ni np/Mg(Al)O catalyst.  Compared with the Fe-Ni IW/Mg(Al)O catalyst, the nanoparticle catalyst was more easily reduced and exhibited enhanced methane dehydrogenation and 5 times longer life-times.  Each reduced Fe-Ni nanoparticle functioned as an active site for the growth of CNTs.  An invar-like Fe-Ni-C alloy phase is believed to be more active phase for methane dehydrogenation than Fe-Ni austenitic phase, Fe metal and metastable Fe-C carbides.  Another effort was the combination of computational and experimental approaches to design shape selective solid base catalysts for the liquid phase furaldehydes condensations with ketones, where the zeolites with desired pore structures and sizes were nitrided in ammonia at the elevated temperatures to replace the bridging oxygens to lower electronegativity nitrogens for the generation of the strong basic sites.  In one of these researches, the nitrogen-substituted NaY showed comparable catalytic activity to MgO-ZrO₂, but higher selectivity to furadehyde acetone monomer product, indicating the shape selective significance of nitrogen-substituted NaY.  The combination of advanced material synthesis with computation, characterization, temperature programmed surface reactions, and kinetic studies provide a useful tool to rational design heterogeneous catalysts.

 

Keywords:  Non-oxidative methane dehydrogenation; monodispersed nanoparticles; nanoparticle catalysts; solid base catalysts; nitrogen-substituted zeolites