Project description:The production of carbon-neutral fuels from CO2 presents an avenue for causing an appreciable effect in terms of volume toward the mitigation of global carbon emissions. To that end, the production of isoparaffin-rich fuels is highly desirable. Here, we demonstrate the potential of a multifunctional catalyst combination, consisting of a methanol producer (InCo) and a Zn-modified zeolite beta, which produces a mostly isoparaffinic hydrocarbon mixture from CO2 (up to ∼85% isoparaffin selectivity among hydrocarbons) at a CO2 conversion of >15%. The catalyst combination was thoroughly characterized via an extensive complement of techniques. Specifically, operando X-ray absorption spectroscopy (XAS) reveals that Zn (which plays a crucial role of providing a hydrogenating function, improving the stability of the overall catalyst combination and isomerization performance) is likely present in the form of Zn6O6 clusters within the zeolite component, in contrast to previously reported estimations.
Project description:Porous organic frameworks (POFs) with a heteroatom rich ionic backbone have emerged as advanced materials for catalysis, molecular separation, and antimicrobial applications. The loading of metal ions further enhances Lewis acidity, augmenting the activity associated with such frameworks. Metal-loaded ionic POFs, however, often suffer from physicochemical instability, thereby limiting their scope for diverse applications. Herein, we report the fabrication of triaminoguanidinium-based ionic POFs through Schiff base condensation in a cost-effective and scalable manner. The resultant N-rich ionic frameworks facilitate selective CO2 uptake and afford high metal (Zn(ii): 47.2%) loading capacity. Owing to the ionic guanidinium core and ZnO infused mesoporous frameworks, Zn/POFs showed pronounced catalytic activity in the cycloaddition of CO2 and epoxides into cyclic organic carbonates under solvent-free conditions with high catalyst recyclability. The synergistic effect of infused ZnO and cationic triaminoguanidinium frameworks in Zn/POFs led to robust antibacterial (Gram-positive, Staphylococcus aureus and Gram-negative, Escherichia coli) and antiviral activity targeting HIV-1 and VSV-G enveloped lentiviral particles. We thus present triaminoguanidinium-based POFs and Zn/POFs as a new class of multifunctional materials for environmental remediation and biomedical applications.
Project description:Supported metal catalysts have shown to be efficient for CO2 conversion due to their multifunctionality and high stability. Herein, we have combined density functional theory calculations with microkinetic modeling to investigate the catalytic reaction mechanisms of CO2 hydrogenation to CH3OH over a recently reported catalyst of Cd4/TiO2. Calculations reveal that the metal-oxide interface is the active center for CO2 hydrogenation and methanol formation via the formate pathway dominates over the reverse water-gas shift (RWGS) pathway. Microkinetic modeling demonstrated that formate species on the surface of Cd4/TiO2 is the relevant intermediate for the production of CH3OH, and CH2O# formation is the rate-determining step. These findings demonstrate the crucial role of the Cd-TiO2 interface for controlling the CO2 reduction reactivity and CH3OH selectivity.
Project description:A new class of TiO2-doped CeO2 nanorods was synthesized via a modified hydrothermal method, and these nanorods were first used as catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH in a fixed-bed reactor. The micromorphologies and physical-chemical properties of nanorods were characterized by transmission electron microscopy, X-ray diffraction, N2 adsorption, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The effects of the TiO2 doping ratio on the catalytic performances were fully investigated. By doping TiO2, the surface acid-base sites of CeO2 nanorods can be obviously promoted and the catalytic activity can be raised evidently. Ti0.04Ce0.96O2 nanorod catalysts exhibited remarkably high activity with a methanol conversion of 5.38% with DMC selectivity of 83.1%. Furthermore, kinetic and mechanistic investigations based on the initial rate method were conducted. Over the Ti0.04Ce0.96O2 nanorod catalyst, the apparent activation energy of the reaction was 46.3 kJ/mol. The reaction rate law was determined to be of positive first-order to the CO2 concentration and the catalyst loading amount. These results were practically identical with the prediction of the Langmuir-Hinshelwood mechanism in which the steps of CO2 adsorption and activation are considered as rate-determining steps.
Project description:A straightforward one-step process was developed, in which CO2 gas is directly converted into multi-layer graphene via atmospheric pressure chemical vapor deposition (APCVD). A bimetallic alloy film based on Cu and Pd was employed as the catalyst and substrate. In this study, we found that the quantity of Cu required for the CO2 conversion process is high (>82 at %). The findings gained in this study serve as a foundation for further studies of metallic alloys for the thermo-reduction of CO2 to graphene under CVD conditions.
Project description:Direct oxidation of methane to value-added C1 chemicals (e.g. HCHO and CO) provides a promising way to utilize natural gas sources under relatively mild conditions. Such conversions remain, however, a key selectivity challenge, resulting from the facile formation of undesired fully-oxidized CO2. Here we show that B2O3-based catalysts are selective in the direct conversion of methane to HCHO and CO (~94% selectivity with a HCHO/CO ratio of ~1 at 6% conversion) and highly stable (over 100 hour time-on-stream operation) conducted in a fixed-bed reactor (550 °C, 100 kPa, space velocity 4650 mL gcat-1 h-1). Combined catalyst characterization, kinetic studies, and isotopic labeling experiments unveil that molecular O2 bonded to tri-coordinated BO3 centers on B2O3 surfaces acts as a judicious oxidant for methane activation with mitigated CO2 formation, even at high O2/CH4 ratios of the feed. These findings shed light on the great potential of designing innovative catalytic processes for the direct conversion of alkanes to fuels/chemicals.
Project description:Although enormous progress has been made in C1 chemistry and CO2 conversion in recent years, it is still a challenge to develop new carbon resource transformation protocols especially those lead to the production of liquid fuels with high selectivity under mild conditions (e.g., under low temperature and using benign solvent). Herein, we present a novel and energy-efficient catalytic route to directly transform CO and H2O to liquid fuels (i.e., liquid hydrocarbons) at low temperature (≤200 °C) in aqueous phase (i.e., in a benign solvent), in which H2O served as both hydrogen source and solvent for the liquid fuel production. The key to the catalytic process is the construction of a highly efficient tandem catalyst Pt-Mo2C/C + Ru/C, which can directly convert CO and H2O in aqueous phase to liquid hydrocarbons with a production rate of 8.7 mol-CH2- molRu-1 h-1 and selectivity up to 68.4% of C5+ hydrocarbons at 200 °C.
Project description:Capture and conversion of CO2 from oceanwater can lead to net-negative emissions and can provide carbon source for synthetic fuels and chemical feedstocks at the gigaton per year scale. Here, we report a direct coupled, proof-of-concept electrochemical system that uses a bipolar membrane electrodialysis (BPMED) cell and a vapor-fed CO2 reduction (CO2R) cell to capture and convert CO2 from oceanwater. The BPMED cell replaces the commonly used water-splitting reaction with one-electron, reversible redox couples at the electrodes and demonstrates the ability to capture CO2 at an electrochemical energy consumption of 155.4 kJ mol-1 or 0.98 kWh kg-1 of CO2 and a CO2 capture efficiency of 71%. The direct coupled, vapor-fed CO2R cell yields a total Faradaic efficiency of up to 95% for electrochemical CO2 reduction to CO. The proof-of-concept system provides a unique technological pathway for CO2 capture and conversion from oceanwater with only electrochemical processes.
Project description:The capture and catalytic conversion of CO2 into value-added chemicals is a promising and sustainable approach to tackle the global warming and energy crisis. The nitrogen-rich porous organic polymers are excellent materials for CO2 capture and separation. Herein, we present a nitrogen-rich heptazine-based microporous polymer for the cycloaddition reaction of CO2 with epoxides in the absence of metals and solvents. HMP-TAPA, being rich in the nitrogen site, showed a high CO2 uptake of 106.7 mg/g with an IAST selectivity of 30.79 toward CO2 over N2. Furthermore, HMP-TAPA showed high chemical and water stability without loss of any structural integrity. Besides CO2 sorption, the catalytic activity of HMP-TAPA was checked for the cycloaddition of CO2 and terminal epoxides, resulting in cyclic carbonate with high conversion (98%). They showed remarkable recyclability up to 5 cycles without loss of activity. Overall, this study represents a rare demonstration of the rational design of POPs (HMP-TAPA) for multiple applications.
Project description:In recent years, bifunctional catalysts for the syngas-to-olefins (STO) reaction via the oxide-zeolite (OX-ZEO) strategy has been intensively investigated. However, the bifunctional catalyst containing H-SSZ-13 with a 100% H+-exchanging degree for the STO reaction has not been developed because of the high selectivity to paraffin. Here, we report a ZnCrO x + H-SSZ-13 bifunctional catalyst, which contains the submicron H-SSZ-13 with adequate acidic strength. Light olefins in hydrocarbon reached 70.8% at a CO conversion of 20.9% over the ZnCrO x + H-SSZ-13(23S) bifunctional catalyst at 653 K, 1.0 MPa, and GHSV = 6000 mL·g-1·h-1 after 800 min of STO reaction. The effect of CO and H2 on the C-C coupling was discussed by carrying out the methanol-to-olefins (MTO) reaction under a similar atmosphere as that of the STO reaction. H2 and CO should play a more dominant role than the conventional hydrogen transfer reaction on the undesired high selectivity of paraffins. These findings provide new insight into the design of the bifunctional catalyst for the STO process via the OX-ZEO strategy.