Advanced Catalysis for Renewable Carbon Conversion: Part 2

The electrochemical CO₂ reduction reaction (CO₂RR) provides a promising pathway to store renewable electricity in chemical bonds; however, operation in strongly acidic media at industrially relevant current densities is typically limited by rapid hydrogen evolution (HER). Here we report a K-doped ZrO₂/CuO reverse heterojunction (denoted K-ZrO₂/CuO) that sustains ampere-class activity in strong acid (pH = 0.5), reaching current densities up to 3.0 A cm^-2 while maintaining suppressed hydrogen production (FE_H₂ ≈ 6% at 2.0 A cm^-2 and ≈ 10% at 3.0 A cm^-2). Compared with CuO and undoped ZrO₂/CuO, the K-modified interface significantly alters the kinetic competition between CO₂RR and HER. By combining theoretical calculations with in situ Raman spectroscopy, we find that K-doping generates a more flexible interfacial water network that facilitates water reorientation and enhances hydrogen proximity to *CO₂, while simultaneously restricting water-mediated proton migration associated with the Volmer process. This selective modulation sustains CO₂ conversion at ampere-class current densities in strongly acidic conditions.

To elucidate CO₂ conversion pathways under mild reaction conditions, we developed a series of Cu-incorporated ZIF (zeolitic imidazolate framework) catalysts for non-thermal plasma–assisted Dielectric barrier-discharge (DBD) reactor for CO₂ hydrogenation at atmospheric pressure and room temperature. By systematically varying the Cu loading (2.5%, 5%, and 10%), the product distribution could be effectively tuned, leading to the formation of CO and CH₄ as primary products, along with the notable generation of C₂H₆. The 10% Cu loaded ZIF catalyst showed promising selectivity towards the formation of C₂H₆. To optimize the process parameters and its effect on C₂H₆ selectivity, the CO₂ hydrogenation reaction is carried out using Design of Experiment (DOE) with Face Centered Composite Design (FCCD). The process parameters considered for DOE study are CO₂ to H₂ ratio (v/v), plasma frequency (kHz) and plasma voltage (kV). Remarkably, the detection of C₂H₆ under ambient conditions is rarely reported in plasma-assisted CO₂ conversion systems, highlighting the unique catalytic behavior of the Cu–ZIF framework. This result indicates a strong synergistic interaction between plasma-induced reactive species and Cu-based active sites, which promotes surface-mediated C–C coupling reactions that are otherwise difficult to achieve under conventional thermal conditions. The porous ZIF structure likely facilitates enhanced dispersion of Cu species and efficient interaction with plasma-activated intermediates, thereby stabilizing carbon-containing radicals and enabling their coupling into higher hydrocarbons. Overall, these findings demonstrate that rational design of metal–organic framework–based catalysts combined with non-thermal plasma offers a promising strategy for low-temperature CO₂ conversion toward value-added C₂ hydrocarbons.

Cyclic and polycarbonate synthesis from CO₂ and epoxides is a promising method of using CO₂ as a C-1 feedstock. Biological sources of unsaturated oils, such as fish and algae oils, can provide olefinic feedstocks, which can be epoxidized via atom-efficient routes. This presentation will describe our efforts to develop catalytic processes that can generate polycarbonates, polyesters and non-isocyanate polyurethanes from a variety of monomers. Catalysts to-date have used a variety of active metal-containing complexes including Zr, Cr, Fe, Co, Ni, Zn-containing systems with diverse multidentate ligands. The amino-bis(phenolate) ligand framework has been our ligand of choice because it is highly modifiable both sterically and electronically. Pairing these ligands is possible with both main group and transition metals and many new complexes have been structurally characterized. A survey of early, mid and late transition metal complexes of amine-bis(phenolate) ligands for polymerization reactions will be described. Co-polymers of CO₂ with epoxides, as well as cyclic ester ring-opening polymerization and ring-opening copolymerization of epoxides with cyclic anhydrides will be presented. Also, the formation of non-isocyanate polyurethanes from the reaction of epoxidized aquatic bio-oils with CO₂ to give cyclic carbonates, followed by curing with polyamine reagents will be discussed.

The growing demand for sustainable chemical processes has aroused interest in studying the conversion of biomass-derived platform molecules, with furfural standing out due to their abundance and versatility. Derived from hemicellulose-rich agricultural residues, furfural serves as a key intermediate for producing fuels, solvents, fine chemicals, and polymers. Among them, the most valuable derivatives are furfuryl alcohol (FA), which is widely used in resins and polymers, and 2-methylfuran (2-MF), a promising biofuel additive with high energy density and favorable combustion properties. However, selective electrochemical hydrogenation (ECH) of furfural to produce 2-MF or FA remains challenging.
This presentation details advancements in the precise synthesis of metal nitride nanoparticles for enhanced electrochemical hydrogenation of furfural. It explores the controllable synthesis, structural characteristics, and catalytic performance of metal nitride nanoparticles for efficient ECH catalysis of furfural. Specifically, it was found that ternary metal nitride is more selective than binary nitride nanoparticles for FF to FA conversion. By exploring the controlled crystal phase and morphologies, we aim to elucidate the structure–activity relationships that govern product selectivity and efficiency of metal nitride nano-catalysts that are crucial for efficient biomass valorization.

Porphyrins are naturally occurring heterocyclic macrocycles that play a central role in oxygen transport, as heme, and in photosynthesis, as chlorophyll. These free-base porphyrins are metalated to form metalloporphyrins and are further modified by adding an electron-donating or withdrawing substituent in the beta positions. These substituents affect the electronic structure of the central metal, and thus, allow the metal-coordinated porphyrins to self-assemble into well-ordered 2D sheets, creating an ideal model system for single-atom catalysis (SAC). In this work, we investigate the self-assembly and electronic behavior of nickel-centered porphyrins with different substituents on Au(111) and Cu(111) surfaces, with particular attention to how the electronically tuned Ni center catalyzes CO₂ adsorption, a key step in activating CO₂ molecules for further conversions. Scanning tunneling microscopy and spectroscopy (STS/STS) were employed to qualitatively probe changes in the local density of states associated with variations in the porphyrin substituents and central metal environment. Subsequent exposure of the assembled monolayers to CO₂ for direct observation of gas surface interactions at well-defined metal centers under confined conditions. The results show that Ni porphyrins form stable, extended two-dimensional networks on both gold and copper substrates characterized by large band gaps. STM and STS measurements indicate that the adsorption of CO₂ molecules is susceptible to influencing the electronic structure of the nickel center, suggesting the ability to finely modulate metal ligand and gas interactions. By isolating and controlling CO₂ interactions at a molecularly defined metal site, this project addresses a key challenge in CO₂ conversion processes. The insights gained contribute to design principles for catalytic systems that rely on precise control of active sites and reaction environments.

Mo⁰ and W⁰ complexes bearing both phosphine and dinitrogen ligands can be synthesized from inexpensive and readily accessible Mo(V) or W(VI) precursors via a one-step, mild reduction. Monodentate, bidentate, and tridentate phosphine ligands were systematically investigated. The distribution of the resulting products is strongly influenced by the coordination environment and the identity of the metal center. The isolated complexes were fully characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopic methods. These studies confirm the coordination modes of the phosphine ligands and the binding of dinitrogen. Importantly, these complexes show potential utility in renewable energy applications, particularly in studies related to olefin metathesis.