59th Annual Report on Research 2014

Background This project focuses on (1) understanding the interactions of reactants and catalyst surfaces and then (2) connecting the structures of reactants and catalytic sites to the kinetic parameters for hydrogenation and C-N bond activation during deep hydrodenitrogenation (HDN) on well-defined, dispersed Ru clusters because of their higher reactivities than conventional Ni or Co promoted Mo based catalysts. We seek to answer the following questions: (1) how do the catalytic surface structures response to changing sulfur chemical potentials, (2) what are the reaction pathways, identity of the kinetically-relevant step, and most abundant surface intermediates, and (3) how does sulfur solvation into the cluster bulk affect the individual rate parameters for the various pathways during hydrodenitrogenation reactions? We address these questions through kinetic, isotopic exchange, and spectroscopic methods. The overall objective is to pinpoint relevant thermochemical properties of catalyst sites as kinetic descriptors and then demonstrate the use of this knowledge to tune the catalyst properties, thus increasing the yields and minimizing hydrogen consumption during hydrodenitrogenation. Research Progress In this reporting period, we explored (1) catalyst synthesis methods to disperse nanometer-sized Ru clusters on inert supports and (2) design and construct a high pressure trickle bed catalytic reactor testing system. Synthesis of Supported Ru Clusters. Several methods of synthesizing well-defined, dispersed Ru catalysts were explored in order to disperse Ru clusters uniformly on high surface area supports. A precipitation method based on the addition of supports (e.g. silica) to aqueous solution containing Ru precursor and NaOH solution at different concentrations of NaOH and temperatures was used to prepare the Ru catalysts and compared with the reference sample prepared from the standard incipient wetness impregnation method. The catalysts were sulfated in a flowing gas mixture of hydrogen sulfide and hydrogen at different hydrogen to hydrogen sulfide ratios, which set the chemical potential of sulfur. The initial dispersion of the Ru clusters was determined using hydrogen chemisorption methods, the sulfur contents after the sulfation step with temperature programmed desorption in flowing hydrogen, and the chemical state of the samples during the various stages were quantified by x-ray photoelectron spectroscopy (XPS). Catalytic System Design, Construction and Startup. A team of undergraduate students, led by a post-doctoral degree candidate, has participated in the design and construction of a high pressure, trickle bed catalyst reactor system, equipped with flow and temperature controls, a high pressure syringe pump, and the appropriate safety measures. A complete process flow diagram with detailed drawings is produced and the construction is completed. The various process flow parameters of the system is calibrated and the system is currently under evaluation using a standard hydrotreating catalyst with 2-methylpyridine or 2-methylpyrrole as the key reactant in hydrogen and hydrogen sulfide mixtures. Preliminary Findings The preliminary findings from the initial phase of the project are: (1) Catalyst preparation, in particular, the pretreatment of the samples after Ru deposition is critical for the decomposition of Ru precursors and their subsequent aggregation to create Ru clusters with narrow size distributions. Uniform Ru clusters are achieved from controlled NaOH addition, drying, and then heating under flowing hydrogen using a slow temperature ramping step. The size distributions and average cluster diameters were confirmed from TEM and hydrogen chemisorption. (2) The extent of sulfation, measured by the amount of sulfur incorporated into the Ru cluster bulk, is related directly to the ratio of hydrogen sulfide-to-hydrogen, and the solvation of sulfur into the bulk appears to be a transport restricted step. Impact on Career of PI and Students This grant has allowed the PI to initiate a new line of research, training i) four undergraduate students (partially supported by departmental research fellowships), ii) a post-doctoral candidate, and iii) a PhD student. The undergraduate students presented their work at the Faculty’s Annual Engineering Research Day in August 2014, and one of them received a practical training opportunity (an internship year) with a catalyst company, in part due to the training in catalysis research provided by this project. The PI has initiated new research collaboration in the parallel area of tandem hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) with Imperial Oil. This grant also enables students to travel to Canadian Light Source next year to carry out in-situ x-rays absorption studies in order to probe the solvation of sulfur into Ru clusters.