Skip to main content Skip to secondary navigation

In Loving Memory of George "Bud" M. Homsy (1943 - 2024)

Main content start

Aditya Bhan

All that most maddens and torments in catalytic CH4 conversion

University of Minnesota

Event Details:

Monday, November 15, 2021
4:00pm - 5:00pm PST

Location

(In Person) Room Y2E2 111

This event is open to:

Alumni/Friends
Faculty/Staff
Students
Aditya Bhan

Aditya Bhan, Ph.D.
Professor, University of Minnesota
Chemical Engineering
Bhan Research Group

Abstract: All that most maddens and torments in catalytic CH4 conversion
The global chemical industry is in transition as it responds to changes in feedstock availability and type.  The availability of natural gas in the United States has renewed interest in catalytic synthesis of fuels and chemicals from light alkanes. We illustrate the formidable kinetic bottlenecks and thermodynamic constraints in selectivity in activating apolar C-H bonds in oxidative and non-oxidative CH4 conversion routes in context of recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on concepts that tackle these ubiquitous challenges.

The first part of this presentation will discuss our efforts in stabilizing highly reactive metal-oxo species in metal-organic framework materials for low temperature oxidative functionalization of alkanes. Specifically, we report the ability of a biomimetic, high-spin (S=2), Fe(II) site, situated in trimeric iron-oxo based nodes of a series of MOFs (MIL-100(Fe), MIL-127(Fe)/PCN-250) – characterized by in-situ X-ray Absorption and ex-situ Mössbauer spectroscopy – to activate light alkanes, including methane. The reaction kinetics and mechanism deduced by varying reactant concentration, temperature, and batch time compare well with DFT cluster calculations and validate a mechanism involving multiple antiferromagnetically-coupled high-spin iron centers in proximity to the active site. Further, we evince, using in situ FTIR in concert with DFT studies, that methanol, the desired product of methane oxidation, is stabilized as surface methoxy groups on the MOF. Pursuant to this, we added a zeolite (MFI, Si/Al = 11.5) co-catalyst in inter- and intra- pellet mixtures with the MOF, and observe monotonic increases in methanol selectivity with increasing ratio and proximity of zeolitic H+ to MOF-based Fe(II) sites, signaling increased amounts of methanol diffusing from the MOF and being dehydrated and protected within the zeolite. This body of work (i) identifies open Fe(II) in high spin configurations in crystalline MOF materials as a class of non-interacting catalytic sites arranged in organized arrays for methane-to-methanol conversion, (ii) demonstrates the radical-rebound mechanism commonly invoked in this chemistry is insufficient to explain the reactivity of these systems, and (iii) offers a potential strategy to mitigate over-oxidation in these and other similar systems.

The second part of this presentation will discuss our efforts on controlling the rate and reversibility of non-oxidative CH4 dehydroaromatization on Mo/ZSM-5. Well-dispersed carbidic Mo aggregates (MoCx) circumscribed in the pores of a medium-pore zeolite, ZSM-5, catalyze CH4 dehydroaromatization (DHA) with high benzene (>70%) and aromatic (>95%) selectivity at conversions near the ~10% equilibrium limit at ~950 K. Net benzene formation rates are limited by reaction endothermicity and approach zero as methane conversion nears the ~10% equilibrium limit. We (i) leverage the “non-selective” deactivation of MoCx/H-ZSM-5 catalysts to discern the connectivity of the methane to benzene reaction network, (ii) demonstrate Mo is the sole kinetically-relevant active site in MoCx/H-ZSM-5 catalysts, and (iii) circumvent thermodynamic barriers to methane DHA by in-situ H2 removal.

Biography:
Aditya Bhan received his Bachelor of Technology (B. Tech.) in Chemical Engineering from IIT Kanpur in 2000 and his PhD in Chemical Engineering from Purdue University in 2005. From January 2005 to August 2007, he was a postdoctoral scholar at the University of California at Berkeley and since then he has been on the Chemical Engineering and Materials Science faculty at the University of Minnesota where he currently serves as the Shell Chair Professor in Chemical Engineering. He leads a research group that focuses on mechanistic characterization of catalysts useful in energy conversion and petrochemical synthesis. His group at the University of Minnesota has been recognized with the Young Researcher Award from the Acid-Base Catalysis Society and the Ipatieff Prize from the American Chemical Society. He serves as Editor for Journal of Catalysis and as Chair of the ACS Catalysis Science & Technology Division.

Explore More Events