Research

The overarching goal of research of Xu lab is to develop efficient and selective heterogeneous thermo- and electro-catalytic processes to enable the production of renewable energy and chemicals. Intellectually, we are curious about the how surface mediated processes enable the thermo- and electro-catalytic transformations on the molecular level. We frequently employ and in many cases develop in-situ/operando spectroscopic techniques, in conjunction with kinetic investigations, to achieve mechanistic understanding. We are also interested in the design, synthesis and characterization of catalytic materials with unique architectures. Below are several directions we are actively pursuing.

 

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Biomass Upgrading

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Key questions:

1) How do the two reaction steps proceed on the molecular level on the catalyst surface?

2) How does solvent affect the properties of catalytic sites and impact reactivity?

3) How to engineer catalyst architecture and site distribution to enable selective tandem catalysis?

 

Below are several recent and ongoing projects in this area:

Encapsulation as a catalyst architecture to enable tandem catalytic upgrading of biomass derived furans

We recently demonstrated that encapsulating metal nanoparticles in zeolites is an effective approach in enabling selective tandem catalysis, e.g., acid catalyzed Aldol condensation followed by metal .mediated hydrogenation.

 

Hydrodeoxygenation (HDO)  of biomass-based furanics to fuels and chemicals via catalytic transfer hydrogenation

We elucidated the reaction mechanism and identified the active sites in the HDO of furfural to 2-methyl furan via isotopic labeling and kinetic studies.

A renewable pathway to adipic acid, a key building block to Nylon, was developed without employing any metal catalyst

Properties of in-situ generated Bronsted acid sites on NaY

Catalytic sites generated via the interaction between reactants and the catalyst could play key roles in selectivity control. For example, in-situ generated Bronsted acid sites are detrimental to the selective dehydration of lactic acid to acrylic acid. We recently determined the Bronsted acid sites generated via the ion-exchange between an organic acid/ester with NaY are fundamentally different from those intrinsic to faujasites. This discovery offers a novel approach to tune the properties of Bronsted acid sites on zeolites. 

 

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Surface-Mediated Electrocatalytic Processes

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013015_kclo4_co_cyc4_vs1100mV_site

Surface enhanced infrared absorption spectroscopy (SEIRAS) results on potential dependent CO adsorption on Pt.

Key questions:

1) How do species in the electrical double layer respond to the applied potential?

2) How do interactions between species in the electrical double layer impact surface mediated electrocatalytic reactions?

3) How are relatively inert molecules activated at the electrochemical interface?

 

Below are several recent and ongoing projects in this area:

Electrochemical Reduction of CO, CO2 and N2

We elucidated the role of bicarbonate in the electrochemical reduction of CO2 on Au.

We identified the active phase of oxide-derived Cu in electrochemical reduction of CO and CO2 to be Cu(100) facet.

We demonstrated VN is an active, selective and durable catalyst for electrochemical N2 reduction, identified the active phase to be the oxynitride, and elucidated the deactivation mechanism.

 

optics

 

 

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Developing Enabling Tools

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Operando Surface Enhanced Infrared Cell

We designed and fabricated the first ever stirred SEIRAS cell, enabling operando investigations.

We constructed a flow ATR cell to investigate the solvent effect on the properties of catalytic sites and reactivity in biomass upgrading.

We built the first liquid phase temperature program desorption and reduction setups.Liquid phase TPD setup.

Liquid phase TPR setup.

 

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Process Intensification Strategies

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We developed the first ever chemical looping reactor for methane dehydroaromatization reaction to circumvent the thermodynamic limitation of non-oxidative methane conversion.


 

Our research is supported by:


NSF DOE

 

eere

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