Enhanced hybrid photocatalytic dry reforming using a phosphated Ni-CeO2 nanorod heterostructure.

Operating the dry reforming reaction photocatalytically presents an opportunity to produce commodity chemicals from two greenhouse gases, carbon dioxide and methane, however, the top-performing photocatalysts presented in the academic literature invariably rely on the use of precious metals. In this work, we demonstrate enhanced photocatalytic dry reforming performance through surface basicity modulation of a Ni-CeO2 photocatalyst by selectively phosphating the surface of the CeO2 nanorod support. An optimum phosphate content is observed, which leads to little photoactivity loss and carbon deposition over a 50-hour reaction period. The enhanced activity is attributed to the Lewis basic properties of the PO43- groups which improve CO2 adsorption and facilitate the formation of small nickel metal clusters on the support surface, as well as the mechanical stability of CePO4. A hybrid photochemical-photothermal reaction mechanism is demonstrated by analyzing the wavelength-dependent photocatalytic activities. The activities, turnover numbers, quantum efficiencies, and energy efficiencies are shown to be on par with other dry-reforming photocatalysts that use noble metals, representing a step forward in understanding how to stabilize ignoble nickel-based dry reforming photocatalysts. The challenges associated with comparing the performance of photocatalysts reported in the academic literature are also commented on.

Solar Urea: Towards a Sustainable Fertilizer Industry.

Urea, an agricultural fertilizer, nourishes humanity. The century-old Bosch-Meiser process provides the world's urea. It is multi-step, consumes enormous amounts of non-renewable energy, and has a large CO2 footprint. Thus, developing an eco-friendly synthesis for urea is a priority. Herein we report a single-step Pd/LTA-3A catalyzed synthesis of urea from CO2 and NH3 under ambient conditions powered solely by solar energy. Pd nanoparticles serve the dual function of catalyzing the dissociation of NH3 and providing the photothermal driving force for urea formation, while the absorption capacity of LTA-3A removes by-product H2 O to shift the equilibrium towards urea production. The solar urea conversion rate from NH3 and CO2 is 87 µmol g-1 h-1 . This advance represents a first step towards the use of solar energy in urea production. It provides insights into green fertilizer production, and inspires the vision of sustainable, modular plants for distributed production of urea on farms.

Anchoring BaII to Pd/Hy WO3-x Nanowires Promotes a Photocatalytic Reverse Water-Gas Shift Reaction.

Surface deposition of BaII on Pd/Hy WO3-x nanowires was developed by using a solution-phase atomic layer deposition process. The procedure involves the generation of Brønsted surface OH sites by H2 spillover on Pd/WO3 , which can then hydrolytically condense with Ba(OEt)2 to produce surface BaII . At just 0.2 at % Ba, CO production by the light-assisted activity of the reverse water-gas shift (RWGS) reaction was observed to increase by about 300 %. In situ DRIFTS studies suggested enhanced CO2 capturing capabilities of a Ba-decorated surface. This study further exemplifies the importance of surface chemistry in optimizing materials for catalysis.

Hybrid Photo- and Thermal Catalyst System for Continuous CO2 Reduction.

Heterogeneous thermal catalytic processes are vital for industrial production of fuels, fertilizers, and other chemicals necessary for sustaining human life. However, these processes are highly energy-intensive, requiring a vast consumption of fossil fuels. An emerging class of heterogeneous catalysts that are thermally driven but also exhibit a photochemically enhanced rate can potentially reduce process energy intensity by partially substituting conventional heat (where fossil fuels are needed) with solar energy. Such catalyst systems have yet to be practically utilized. Here, we demonstrate a compact electrically heated photo- and thermal annular reactor module to reduce CO2 to CO, via the reverse water gas shift reaction. A first-principles-based design approach was taken in developing a SiO2 on an Al photo- and thermal catalyst system for the model photo- and thermal indium oxide hydroxide (In2O3-x(OH)y) catalysts. A 5-fold light enhancement in the CO production rate and over 70 h of stable CO production were achieved. This represents the highest light enhancement effect reported for this model photocatalyst to date. The reactor presented herein allows continuous operation and a significant reduction of 31% in heater power consumption when provided with an additional 2 suns of irradiation, demonstrating the strong photo- and thermal-harvesting performances of the catalyst system developed in this work.

Cu Atoms on Nanowire Pd/HyWO3-x Bronzes Enhance the Solar Reverse Water Gas Shift Reaction.

Nanowire hydrogen bronzes of WO3 nanowires decorated with Pd (Pd/HyWO3-x) were previously demonstrated to effectively capture broadband radiation across the ultraviolet to near-infrared wavelength range and catalyze the reverse water gas shift reaction (RWGS). Herein, we report a synthetic strategy to enhance the performance of this class of photocatalysts by conformally coating Cu atoms onto the surface of Pd/HyWO3-x by anchoring Cu(I)OtBu to the Brønsted acidic protons of the bronze. The resulting materials are characterized by a suite of analytical methods, including electron microscopy and X-ray absorption spectroscopy. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated that for the light-driven RWGS reaction, as little as 0.2 at. % Cu facilitates the formation of surface carboxylate species from CO2, resulting in a 300-500% enhancement in the rate of CO production. This metal anchoring method enables atom precise modification of the surfaces of metal oxide nanomaterials for catalytic applications, circumventing the need for complex and expensive atomic layer deposition processes.

Nickel@Siloxene catalytic nanosheets for high-performance CO2 methanation.

Two-dimensional (2D) materials are of considerable interest for catalyzing the heterogeneous conversion of CO2 to synthetic fuels. In this regard, 2D siloxene nanosheets, have escaped thorough exploration, despite being composed of earth-abundant elements. Herein we demonstrate the remarkable catalytic activity, selectivity, and stability of a nickel@siloxene nanocomposite; it is found that this promising catalytic performance is highly sensitive to the location of the nickel component, being on either the interior or the exterior of adjacent siloxene nanosheets. Control over the location of nickel is achieved by employing the terminal groups of siloxene and varying the solvent used during its nucleation and growth, which ultimately determines the distinct reaction intermediates and pathways for the catalytic CO2 methanation. Significantly, a CO2 methanation rate of 100 mmol gNi-1 h-1 is achieved with over 90% selectivity when nickel resides specifically between the sheets of siloxene.

Pd@H yWO3- x Nanowires Efficiently Catalyze the CO2 Heterogeneous Reduction Reaction with a Pronounced Light Effect.

The design of photocatalysts able to reduce CO2 to value-added chemicals and fuels could enable a closed carbon circular economy. A common theme running through the design of photocatalysts for CO2 reduction is the utilization of semiconductor materials with high-energy conduction bands able to generate highly reducing electrons. Far less explored in this respect are low-energy conduction band materials such as WO3. Specifically, we focus attention on the use of Pd nanocrystal decorated WO3 nanowires as a heretofore-unexplored photocatalyst for the hydrogenation of CO2. Powder X-ray diffraction, thermogravimetric analysis, ultraviolet-visible-near infrared, and in situ X-ray photoelectron spectroscopy analytical techniques elucidate the hydrogen tungsten bronze, H yWO3- x, as the catalytically active species formed via the H2 spillover effect by Pd. The existence in H yWO3- x of Brønsted acid hydroxyls OH, W(V) sites, and oxygen vacancies (VO) facilitate CO2 capture and reduction reactions. Under solar irradiation, CO2 reduction attains CO production rates as high as 3.0 mmol gcat-1 hr-1 with a selectivity exceeding 99%. A combination of reaction kinetic studies and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements provide a valuable insight into thermochemical compared to photochemical surface reaction pathways, considered responsible for the hydrogenation of CO2 by Pd@H yWO3- x.

Heterogeneous catalytic hydrogenation of CO2 by metal oxides: defect engineering - perfecting imperfection.

Metal oxides with their myriad compositions, structures and bonding exhibit an incredibly diverse range of properties. It is however the defects in metal oxides that endow them with a variety of functions and it is the ability to chemically tailor the type, population and distribution of defects on the surface and in the bulk of metal oxides that delivers utility in different applications. In this Tutorial Review, we discuss how metal oxides with designed defects can be synthesized and engineered, to enable heterogeneous catalytic hydrogenation of gaseous carbon dioxide to chemicals and fuels. If this approach to utilization and valorization of carbon dioxide could be developed at industrially significant rates, efficiencies and scales and made economically competitive with fossil-based chemicals and fuels, then carbon dioxide refineries envisioned in the future would be able to contribute to the reduction of greenhouse gas emissions, ameliorate climate changes, provide energy security and enable protection of the environment. This would bring the vision of a sustainable future closer to reality.

Efficient Electrocatalytic Reduction of CO2 by Nitrogen-Doped Nanoporous Carbon/Carbon Nanotube Membranes: A Step Towards the Electrochemical CO2 Refinery.

Herein we introduce a straightforward, low cost, scalable, and technologically relevant method to manufacture an all-carbon, electroactive, nitrogen-doped nanoporous-carbon/carbon-nanotube composite membrane, dubbed "HNCM/CNT". The membrane is demonstrated to function as a binder-free, high-performance gas diffusion electrode for the electrocatalytic reduction of CO2 to formate. The Faradaic efficiency (FE) for the production of formate is 81 %. Furthermore, the robust structural and electrochemical properties of the membrane endow it with excellent long-term stability.

Amine(imine)diphosphine iron catalysts for asymmetric transfer hydrogenation of ketones and imines.

A rational approach is needed to design hydrogenation catalysts that make use of Earth-abundant elements to replace the rare elements such as ruthenium, rhodium, and palladium that are traditionally used. Here, we validate a prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines, with isopropanol as the hydrogen donor, at turnover frequencies as high as 200 per second at 28°C. We present a direct synthetic approach to enantiopure ligands of this type that takes advantage of the iron(lI) ion as a template. The catalytic mechanism is elucidated by the spectroscopic detection of iron hydride and amide intermediates.