Proteomes reveal metabolic capabilities of Yarrowia lipolytica for biological upcycling of polyethylene into high-value chemicals.

IMPORTANCE: Sustainable processes for biological upcycling of plastic wastes in a circular bioeconomy are needed to promote decarbonization and reduce environmental pollution due to increased plastic consumption, incineration, and landfill storage. Strain characterization and proteomic analysis revealed the robust metabolic capabilities of Yarrowia lipolytica to upcycle polyethylene into high-value chemicals. Significant proteome reallocation toward energy and lipid metabolisms was required for robust growth on hydrocarbons with n-hexadecane as the preferential substrate. However, an apparent over-investment in these same categories to utilize complex depolymerized plastic (DP) oil came at the expense of protein biosynthesis, limiting cell growth. Taken together, this study elucidates how Y. lipolytica activates its metabolism to utilize DP oil and establishes Y. lipolytica as a promising host for the upcycling of plastic wastes.

Control of Selectivity through a New Hydrogen-Transfer Mechanism in Photocatalytic Reduction Reactions: Electronically Relaxed Neutral H and the Role of Electron-Phonon Coupling.

Controlling the fate of hydrogen in photocatalytic synthesis reactions has been an ongoing challenge in CO2 reduction by H2O and nitrogen fixation efforts. Our studies have identified catalysts (SiC) that exhibit dramatically improved selectivity toward hydrogenation and a photocatalytically active ground-state neutral H that is transferred via vibrational excitation through electronic-vibrational coupling with excited states. This new species and mechanism have been directly connected to the fate of H by comparing GaN and SiC and purposefully manipulated over a single catalyst (SiC) to illustrate generality. Studies included surface reaction modeling using density functional theory (DFT), experimental performance, 1H NMR spectroscopy, and deuterium kinetic isotope effect. The discovery of this mechanism may have considerable impact on the direction of photocatalytic synthesis, the understanding of the coupling of thermal and photoelectrochemical reaction steps, and electronic-vibrational spectrum coupling in energy sequestration.

Selective and Stable Non-Noble-Metal Intermetallic Compound Catalyst for the Direct Dehydrogenation of Propane to Propylene.

A non-noble intermetallic compound catalyst consisting of Ni3Ga nanoparticles supported on Al2O3 that exhibits high selectivity (∼94%), comparable activity (TOF = 4.7 × 10-2 s-1), good stability (∼94% to 81% over the 82 h test), and regenerability in the direct dehydrogenation of propane to propylene at 600 °C has been developed. Through synthesis techniques that stabilize the Ni3Ga phase, the surface composition of the catalytic nanoparticles could be tuned by Ni and Ga loading such that improved selectivity toward propylene may be achieved. Comparisons with well-defined silica-supported Ni3Ga and NiGa catalysts and Ni3Ga/Al2O3 with a range of Ni:Ga loading suggested that a specific surface composition range was most promising for propylene production. The presence of Ni at the active particle surface was also found to be critical to drive dehydrogenation and enhance conversion, whereas the presence of Ga was necessary to attenuate the reactivity of the surface to improve selectivity and catalyst stability.

Geometric and electronic characteristics of active sites on TiO2-supported Au nano-catalysts: insights from first principles.

Quantum chemical and ab initio thermodynamic calculations were used to investigate the mechanism of CO oxidation on Au/TiO(2) and the geometric and electronic character of active sites. We show that CO oxidation over Au/TiO(2) might proceed via a two site mechanism with oxygen adsorbing and dissociating at the Au/oxide interface or the perimeter of Au particles and CO adsorbing on Au sites away from the interface. The electronic fingerprint of active Au is a function of external conditions, and it is likely that most Au atoms are populated by CO and electronically neutral. Under highly oxidizing conditions, the Au/oxide interface can accommodate oxygen adsorbates, and these Au atoms will have a cationic fingerprint due to their interaction with oxygen. The choice of precursors used to synthesize catalysts as well as the catalyst preparation and pretreatment procedures significantly affect the electronic characteristics and catalytic activity of Au nano-structures. Based on our first-principles analysis we propose a hypothesis that might help us understand these experimental observations.

Oxidation catalysis by oxide-supported Au nanostructures: the role of supports and the effect of external conditions.

Oxide-supported Au nanostructures are promising low-temperature oxidation catalysts. It is generally observed that Au supported on reducible oxides is more active than Au supported on irreducible oxides. Recent studies also suggest that cationic Au(delta+) is responsible for the unique Au/oxide catalytic activity, contrary to the conventional perception that oxide supports donate electronic charge to Au. We have utilized density functional calculations and ab initio thermodynamic studies to investigate the oxidation state of Au nanostructures deposited on reducible and irreducible supports. We find that there are fundamental differences in the electronic structure of Au deposited on the different oxides. We propose a simple model, grounded in the first principles calculations, which can explain the oxide-specific catalytic activity of Au nanostructures and which can account for the presence and the role of cationic Au(delta+).