Mind the gaps in CO₂-to-methanol

Catalysts respond to reactive atmospheres, leading to intrinsically distinct active sites and reaction pathways in response to pressure changes. The degree of pressure gap depends on the nanostructure. Now, the gaps and discrepancies in in-situ and operando studies of CO2-to-CH3OH using CuZn catalysts have been rationalized.Accepted Author ManuscriptChemE/Catalysis Engineerin

PEM Electrolysis-Assisted Catalysis Combined with Photocatalytic Oxidation towards Complete Abatement of Nitrogen-Containing Contaminants in Water

Electrolysis-assisted nitrate (NO3−) reduction is a promising approach for its conversion to harmless N2 from waste, ground, and drinking water due to the possible process simplicity by in-situ generation of H2/H/H+ by water electrolysis and to the flexibility given by tunable redox potential of electrodes. This work explores the use of a polymer electrolyte membrane (PEM) electrochemical cell for electrolysis-assisted nitrate reduction using SnO2-supported metals as the active cathode catalysts. Effects of operation modes and catalyst materials on nitrate conversion and product selectivity were studied. The major challenge of product selectivity, namely complete suppression of nitrite (NO2−) and ammonium (NH4+) ion formation, was tackled by combining with simultaneous photocatalytic oxidation to drive the overall reaction towards N2 formation.ChemE/Catalysis Engineerin

Enabling complete conversion of CH₄ and CO₂ in dynamic coke-mediated dry reforming (DC-DRM) on Ni catalysts

Dynamic coke-mediated dry reforming of methane (DC-DRM) is an unsteady-state strategy to overcome the limitations of co-feed operation, including the fast deactivation of the catalysts and the loss of valuable H2 in the reverse water gas-shift reaction. This paper proves the feasibility of DC-DRM on Ni-based catalytic systems, identifying suitable metal oxides supports and evaluating the role of metallic promoters. A La-promoted Ni/ZrO2 catalyst exhibited excellent and stable catalytic performances at 800 °C approaching complete conversion of the CH4 and CO2 reactant pulses in the reaction loop, and separation of the H2 and CO product streams. Adding the redox functionality of reducible oxides (TiO2) in the catalyst support is demonstrated as a powerful tool to enable direct formation of syngas in the methane pulse with control on the H2/CO ratio.ChemE/Catalysis Engineerin

Electrochemical Conversion of NO to NH₃ in a PEM Cell

The continuous electrochemical NO reduction to ammonia in a PEM cell was investigated in this work. We used a ruthenium-based catalyst at the cathode and an iridium oxide catalyst at the anode. The highest ammonia faradaic efficiency was observed at 1.9 V cell voltage. Adjusting the NO flow allowed to achieve 97% NO conversion and 93% ammonia faradaic efficiency for a 5.2% NO/He feed. The ammonia yield was 0.51 mmol cm-2 h-1, among the highest reported to date with the advantage of continuous operation. Experiments with a low NO concentration feed of 983 ppm showed 98% conversion at 0 V vs pseudo-RHE. Achieving this performance under such mild conditions indicates the great potential of the PEM cells for NOx abatement applications and the production of valuable NH3ChemE/Catalysis Engineerin

Catalytic Oxidative Coupling of Methane: Heterogeneous or Homogeneous Reaction?

Direct valorization of methane via oxidative coupling of methane (OCM) is an encouraging alternative to conventional oil-based processes for the production of light hydrocarbons (ethane and ethylene). Abundant, inexpensive simple oxides such as MgO and La2O3 possess the ability to selectively activate methane. However, during OCM, the selective conversion to ethane and the following dehydrogenation to ethylene are threatened by the thermodynamically favored partial and total oxidation reactions to form CO and CO2, respectively. With the aid of spatially resolved operando analysis of temperature and gas concentration along the catalytic bed, we demonstrate the relevance of highly exothermic reaction paths developed in the gas phase, i.e., the homogeneous reaction, during OCM conditions at the front of the catalytic bed, largely determining the total C2 yield obtained on those systems. With the new insights provided by the analysis of temperature and concentration gradients along the bed, we redefine the positive effect of promoters (Li, Sr), which enhance the influence of catalyst surfaces. The effect of promoters is recognized in the suppression of the exothermic oxidation paths leading to undesired COx, thus limiting the formation of hotspots and driving the reaction toward the desired C2 products.ChemE/Catalysis Engineerin

Electrified Conversion of Contaminated Water to Value: Selective Conversion of Aqueous Nitrate to Ammonia in a Polymer Electrolyte Membrane Cell

The application of a polymer electrolyte membrane (PEM) electrolytic cell for continuous conversion of nitrate, one of the contaminants in water, to ammonia at the cathode was explored in the present work. Among carbon-supported metal (Cu, Ru, Rh and Pd) electrocatalysts, the Ru-based catalyst showed the best performance. By suppressing the competing hydrogen evolution reaction at the cathode, it was possible to reach 94 % faradaic efficiency for nitrate reduction towards ammonium. It was important to match the rate of the anodic reaction with the cathodic reaction to achieve high faradaic efficiency. By recirculating the effluent stream, 93 % nitrate conversion was achieved in 8 h of constant current electrolysis at 10 mA cm−2 current density. The presented approach offers a promising path towards precious NH3 production from nitrate-containing water that needs purification or can be obtained after capture of gaseous NOx pollutants into water, leading to waste-to-value conversion.ChemE/Catalysis Engineerin

Greener and facile synthesis of Cu/ZnO catalysts for CO₂hydrogenation to methanol by urea hydrolysis of acetates

Cu/ZnO-based catalysts for methanol synthesis by COx hydrogenation are widely prepared via co-precipitation of sodium carbonates and nitrate salts, which eventually produces a large amount of wastewater from the washing step to remove sodium (Na+) and/or nitrate (NO3-) residues. The step is inevitable since the remaining Na+ acts as a catalyst poison whereas leftover NO3- induces metal agglomeration during the calcination. In this study, sodium- and nitrate-free hydroxy-carbonate precursors were prepared via urea hydrolysis co-precipitation of acetate salt and compared with the case using nitrate salts. The Cu/ZnO catalysts derived from calcination of the washed and unwashed precursors show catalytic performance comparable to the commercial Cu/ZnO/Al2O3 catalyst in CO2 hydrogenation at 240-280 °C and 331 bar. By the combination of urea hydrolysis and the nitrate-free precipitants, the catalyst preparation is simpler with fewer steps, even without the need for a washing step and pH control, rendering the synthesis more sustainable. This journal is ChemE/Catalysis Engineerin

The 12th International Conference on Environmental Catalysis (ICEC2022), Osaka (Japan), July 30th – August 2nd, 2022

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Catalysis Engineerin

Lewis acidic supports promote the selective hydrogenation of carbon dioxide to methyl formate in the presence of methanol over Ag catalysts

Silica-supported silver nanoparticles exhibit outstanding efficiency in the CO2 hydrogenation to methyl formate in the presence of methanol under high pressure. Here, we show that ZrO2 and Al2O3 supports significantly increase the catalyst activity, in line with their higher Lewis acidity. The weight time yield of methyl formate over Ag/ZrO2 is up to 16.2 gMF gAg h−1 without detectable side-products, 25 times higher compared to Ag/SiO2 at the same temperature. Transient in situ and operando DRIFTS studies uncover spillover processes of formate species from Ag onto the acidic support materials and show that the surface formates can further react with adsorbed methanol at the sites near the perimeter between Ag and the support to yield methyl formate.ChemE/Catalysis Engineerin

Mechanistic insights into the CO₂ capture and reduction on K-promoted Cu/Al₂O₃ by spatiotemporal operando methodologies

Integrated CO2 capture and conversion processes bring the promise of drastic abatement of CO2 emission together with its valorisation to chemical building blocks such as CH4 and CO. Isothermal CO2 capture and reduction (CCR) on a K-promoted Cu/Al2O3 was recognised as an effective catalytic strategy for removing CO2 from diluted stream and converting it to syngas (H2 + CO) employing green H2 as reducing agent. The dual functionality of the catalyst is the key of this dynamic process, in which the alkaline metal introduces the capture functionality and copper ensures the selective conversion of the captured CO2 to CO. However, the highly dynamic state of the catalyst at reaction conditions represents a barrier for the identification of the catalytic mechanism of CCR, which is vital for rational process improvement and design. In this work, we conducted a mechanistic investigation of CCR by means of spatiotemporal operando methodologies, gaining insights into dynamic variation of temperature, gas concentration and reactive surface species in the CCR reactor. The results show the unique potassium state exothermically captures CO2 as surface carbonates which can be reduced to CO rapidly under H2 atmosphere. When the surface carbonates are transformed to formates the reaction path is altered and the reduction to CO becomes slower. By designing controlled catalytic experiments, we further demonstrate the active involvement of CO in the capture mechanism and the effectiveness of CO2 capture in presence of an oxidised surface, extending the perspectives and suitability of CCR to treat actual complex effluent streams.ChemE/Catalysis Engineerin