Cegelski, Lynette | Search NASA

DOE OSTI2024

Unveiling the Stability of Encapsulated Pt Catalysts Using Nanocrystals and Atomic Layer Deposition

Platinum exhibits desirable catalytic properties, but it is scarce and expensive. Optimizing its use in key applications such as emission control catalysis is important to reduce our reliance on such a rare element. Supported Pt nanoparticles (NPs) used in emission control systems deactivate over time because of particle growth in sintering processes. Here, in this work, we shed light on the stability against sintering of Pt NPs supported on and encapsulated in Al 2 O 3 using a combination of nanocrystal catalysts and atomic layer deposition (ALD) techniques. We find that small amounts of alumina overlayers created by ALD on preformed Pt NPs can stabilize supported Pt catalysts, significantly reducing deactivation caused by sintering, as previously observed by others. Combining theoretical and experimental insights, we correlate this behavior to the decreased propensity of oxidized Pt species to undergo Ostwald ripening phenomena because of the physical barrier imposed by the alumina overlayers. Furthermore, we find that highly stable catalysts can present an abundance of under-coordinated Pt sites after restructuring of both Pt particles and alumina overlayers at a high temperature (800 °C) in C 3 H 6 oxidation conditions. The enhanced stability significantly improves the Pt utilization efficiency after accelerated aging treatments, with encapsulated Pt catalysts reaching reaction rates more than two times greater than those of a control supported Pt catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Molecular organization of the E. coli cellulose synthase macrocomplex

Cellulose is frequently found in communities of sessile bacteria called biofilms. Escherichia coli and other enterobacteriaceae modify cellulose with phosphoethanolamine (pEtN) to promote host tissue adhesion. The E. coli pEtN cellulose biosynthesis machinery contains the catalytic BcsA–B complex that synthesizes and secretes cellulose, in addition to five other subunits. The membrane-anchored periplasmic BcsG subunit catalyzes pEtN modification. Here we present the structure of the roughly 1 MDa E. coli Bcs complex, consisting of one BcsA enzyme associated with six copies of BcsB, determined by single-particle cryo-electron microscopy. BcsB homo-oligomerizes primarily through interactions between its carbohydrate-binding domains as well as intermolecular beta-sheet formation. The BcsB hexamer creates a half spiral whose open side accommodates two BcsG subunits, directly adjacent to BcsA’s periplasmic channel exit. The cytosolic BcsE and BcsQ subunits associate with BcsA’s regulatory PilZ domain. As a result, the macrocomplex is a fascinating example of cellulose synthase specification.

59 BASIC BIOLOGICAL SCIENCES↗