Professors Friederike Jentoft and Wei Fan of the Chemical Engineering Department collaborated on a team of chemists and chemical engineering researchers that received a $259,528 grant from the National Science Foundation (NSF) and its Major Research Instrumentation program to acquire a new, state-of-the-art “powder X-ray diffractometer” (PXRD). The team is led by Kevin Kittilstved, assistant professor of chemistry. The College of Engineering and College of Natural Sciences are also cooperating with the Office of the Vice Chancellor for Research and Engagement to contribute another $111,227 toward the purchase of the new apparatus, expected to go into service in early 2018.
In general, Jentoft will utilize the new diffractometer to study and understand the phase chemistry in metal carbide catalysts, while Fan will use the instrument to investigate the crystallization processes during zeolite synthesis.
“I am excited that we will have the in-house capability to watch catalysts form and transform by PXRD and thereby gain novel insights about catalytically active phases,” says Jentoft. “I also believe the instrument will create new opportunities for collaboration.”
In addition to Jentoft and Fan, Kittilstved’s other co-investigator on the successful NSF proposal is Dhandapani Venkataraman of the Chemistry Department.
As Kittilstved explains, “A powder X-ray diffractometer probes solid materials with X-rays to reveal their internal composition and structure. Successful research conducted with this instrument enables investigators to synthesize new materials with the potential to promote society’s transition to sustainable fuels and energy.”
A PXRD is an important instrument for catalysis research because a large fraction of solid catalysts are composed of crystalline inorganic materials. Two major uses of the in situ PXRD are: studying the formation of crystalline phases during catalyst synthesis; and monitoring the alteration or degradation of crystalline phases during a catalytic process. In addition, PXRD measurements are routinely used to guide catalyst synthesis and can, for example, be performed to determine whether the correct phase was obtained or sufficient dispersion of the supported species was obtained.
Research in the Jentoft and Fan research groups would benefit in several ways from the use of a PXRD. According to the successful NSF proposal, the Jentoft group studies transition metal carbides, meaning the phase transformations during synthesis and catalytic operation. Specifically, the Jentoft group is developing synthesis methods for mixed metal carbides and oxycarbides.
As the NSF proposal states: “Motivation for this research comes from transition metal carbides such as Mo₂C and W₂C which exhibit catalytic properties similar to those of noble metals; for example, they catalyze hydrocarbon transformations including isomerization, hydrogenation, and dehydrogenation and hydrogenolysis. Since they are less expensive and often more robust than noble metals, transition metal carbides have been considered as catalysts in a number of applications.”
For instance, transition metal carbides are used in the industrially important process of hydrotreating, that is, hydrodesulfurization and hydrodenitrogenation of conventional feedstocks. More recently, such carbides have been employed in the hydrodeoxygenation of renewable, biomass-derived feedstocks. Another intriguing application is the use of carbides as electrodes or electrode supports in fuel or solar cells.
However, “notwithstanding the potential of carbides, only few materials have been synthesized with high surface area and extensively tested and characterized,” as the NSF proposal notes. Consequently, “the objectives of the Jentoft group’s proposed research are to gain insights in carbide phase formation and to use this knowledge to develop synthesis methods for new families of high-surface area carbides and to understand the dynamic character of carbides during catalytic operation.”
In situ PXRD would allow the group to base carbide synthesis on fundamental understanding of the underlying phase chemistry and develop guidelines for the rational synthesis of new families of catalysts for a variety of important applications. In addition, PXRD analysis and insight into the catalyst phase chemistry will allow the optimization of the catalytic operation and an informed synthesis of the bimetallic carbides under study.
The PXRD will also be invaluable for the research into sustainable fuels being performed by Fan’s group. “The overarching goal of the proposed work and the other research in the Fan group is the rational synthesis of zeolite catalysts with tunable structure, composition, and morphology for applications in catalysis, in particular, the conversion of biomass into sustainable chemicals,” explains the NSF proposal.
As the NSF proposal describes, the ever increasing need for sustainable fuels, chemicals, and medicines has motivated the discovery of advanced materials such as new zeolites and mesoporous silica solids. Zeolites are silica-based porous materials with various heteroatoms and different catalytic active sites. Because of their stability, selectivity, and activity, zeolites have become the most highly used catalysts by mass in the world. As just one example, zeolites are used for the conversion of biomass into sustainable chemicals and carbon-neutral liquid transportation fuels.
The challenge in the development of zeolites with new structure, composition, and morphology is lack of fundamental understanding of the zeolite crystallization process and the capacity of controlling the ring structures of the synthesis gel at molecular levels, as the NSF proposal notes.
Fan’s section of the proposal concludes that “Using the in situ powder X-ray diffractometer proposed in this MRI proposal, we will in situ study the crystallization process of zeolites and control the structures of the synthesis gel by introducing different heteroatoms and organic structure directing agents.” (August 2017)