RWGS Reaction Research Articles

Optimizing reverse water gas shift catalysis: Minimizing metal loading and enhancing performance with Pt/ZrO2 catalysts through Rh incorporation

In this study, the optimization of catalysts for the reverse water gas shift reaction by minimizing metal loading and enhancing the performance of supported Pt catalysts through Rh incorporation was done. The catalysts were synthesized by the wet impregnation method, in which the metal noble load in bimetallic samples decreased by approximately one-third compared to the reference platinum catalyst, with varying Rh-Pt ratios. In all materials, m-ZrO2, obtained by the hydrothermal method, was used as support. In the catalytic tests in a continuous packed-bed flow reactor at atmospheric pressure, all samples were active to catalyze CO2 reduction between 200 and 300 °C. Bimetallic samples, particularly those with an Rh-Pt atomic ratio of 20–80, exhibited superior performance in the RWGS reaction despite their lower metal content. Based on the results of H2-TPR, FTIR in situ, and XPS, we propose that the enhanced CO production in bimetallic samples compared to Pt/ZrO2 catalysts can be attributed to Rh increasing the reduction extent of supported Pt. This enhancement facilitates the hydrogenation of bicarbonate species into formate species, which subsequently evolve into Pt0-CO and ultimately into CO. Additionally, Rh incorporation enables an alternative pathway for CO generation, where Pt0-carbonyls, known for their CO-producing capability, are formed via CO2 dissociation on the Pt0 surface. However, higher Rh concentrations favor the CO2 methanation rather than the RWGS reaction.

CuOx supported LaCoO3 perovskite for the photoassisted reverse water gas shift reaction at low temperature

CuOx/LaCoO3 systems have been studied for the rWGS reaction under thermal assisted photocatalytic conditions within low temperature range of 180–330 ºC. CuOx species deposited from chemical reduction method over LaCoO3 homogeneously covered the perovskite surface. The reduction pretreatment before reaction leads to the partial Co reduction and the complete reduction of Cu. A significant improvement on CO production has been attained upon Cu incorporation. In addition, upon UV–vis irradiation the CO production is also enhanced. Best results have been obtained for 5 wt% Cu. The highest synergistic effect was observed for the lowest temperature, for which catalytic contribution is negligible. Thus, a good compromise is attained at 300 ºC for which a CO production of 5.45 mmol/h·g and 92 % selectivity, showing a good synergistic effect between thermo and thermo-photocatalytic activity.

Selective reduction of CO2 to CO over alumina-supported catalysts of group 5 transition metal carbides

We show the applicability of a preparation method, previously reported for obtaining tailored bulk VCx catalysts, for alumina-supported G5TMCs. The characteristics of the G5TMCs/Al2O3 catalysts and their behaviour in the selective reduction of CO2 to CO through the RWGS reaction is reported. VCx/Al2O3 catalysts were active, stable and highly selective; meanwhile NbC/Al2O3 and TaC/Al2O3 were not active. VCx/Al2O3 catalysts exhibited selectivity to CO over 99.5 % at temperature above 773 K. The characteristics of alumina-supported vanadium carbide particles depended on the vanadium precursor and on the atmosphere used during the catalyst preparation. XPS characterization of VCx/Al2O3 catalysts revealed the presence of carbide species on surface before and after RWGS reaction. The catalytic behaviour of VCx/Al2O3 is analysed in the light of their characteristics and compared with bulk VCx counterparts. The most performant catalyst, VC(Pr)/Al2O3, was stable over 4 days at 723 K, with ∼100 % selectivity to CO and CO2 conversion of ∼11 %.

CO2 hydrogenation to methanol on efficient Pd modified α-MoC1−x catalysts

It is a potentially desirable process of utilizing CO2 as a feedstock to make valuable chemicals such as methanol. Results from the current study demonstrate Pd modified α-MoC1−x is a high active and selective catalyst for CO2 hydrogenation to methanol. α-MoC1−x is active for both methanol synthesis and RWGS reaction. The addition of 0.1 wt% Pd to α-MoC1−x decreases the CO2 hydrogenation reaction activation energy and increases the CH3OH selectivity due to the H2 spillover effect of Pd. RWGS + CO-hydro pathway as a non-competitive parallel pathway to the dominant formate pathway is verified on Pd/α-MoC1−x/C-N, which increases threefold methanol STY compared with α-MoC1−x/C-N catalyst. This work supplies a feasible strategy for creating a dual active site to enhance the efficiency of methanol synthesis.

Effect of Contact Time on Carbon Deposition and Catalytic Activity of Nickel Alumina Catalysts for Dry Reforming of Methane

AbstractDry reforming of methane (DRM) reaction is advantageous in producing syngas with a low H2/CO, relevant to many industries. Effect of contact time on catalytic activity and carbon deposition is studied for DRM using Ni−Al catalysts, along with the effect of metal loading, reaction temperature, and reactant partial pressure (CO2/CH4). Maximum CH4 conversion (58 %) and CO2 (59 %) were achieved at a higher contact time of 4.009 kg‐cat . h/kgCH4. A maximum of 46 % CH4 conversion was achieved at 1023 K with a contact time of 0.134 kg‐cat . h/kgCH4. Higher CH4 and CO2 conversion were achieved with an excellent H2 and CO yield due to the RWGS reaction with increased metal (Ni) loading (10–30 wt . %). When the reactant partial pressure (CO2) changed from 0.1–0.3, the CH4 conversion increased whereas CO2 conversion decreased. FESEM images revealed the formation of whisker‐like carbon fibers for all loadings. For the best syngas output and stability in a Ni‐based catalyst, a combination of a basic support (alumina) at a higher contact time (~4.009 kg‐cat . h/kgCH4) and a CO2/CH4 ratio of 1–1.5 at a moderate temperature of 873 K may provide best CO2 adsorption with minimal coking.

Deciphering the dynamic structural evolution of oxygen vacancies enriched SrFe12O19 for efficient reverse water gas shift reaction

The Reverse Water-Gas Shift (rWGS) reaction is recognized as a potentially promising pathway to serve the dual purpose, possible shifting of CO2 from a linear economy to a circular and positive economic impact in the current industrial process. This study is engaged to develop a series of oxygen vacancies enriched M−type strontium hexaferrite (SrFe12O19) catalysts via doping of transition metals like Cu, Zn, Co, and Ni for the rWGS reaction. Cu-doped SrFe12O19 exhibited 100 % CO selectivity and a CO production rate of 2850 mmol h−1 gcat-1, at a comparatively lower temperature (500 °C), outpacing the performance of almost all non-precious metal-based catalytic systems. Moreover, the catalyst was active without the requirement of the H2 pre-reduction procedure and displayed remarkable stability tested up to 200 h without any significant deactivation, making it more industrially relevant. The characterization of as-prepared catalysts indicates the enrichment of oxygen vacancies and reducibility after the involvement of the dopant in the SrFe12O19 system. The formation of various iron species (Fe3O4, Fe3C, and Fe5C2) was revealed by the in-situ studies and post-reaction characterizations of the catalyst system, and their relative amounts were significantly affected by the nature of doping elements, which subsequently influenced the CO selectivity. The dynamic structural evolution and surface-adsorbedspecies were identified usingin-situ Raman and DRIFTS studies. Finally, the structure–activity relationship was rationalized through not only several ex-situ/in-situ characterization techniques but also an in-detailed Density functional theory (DFT) study.

Experimental investigation of photo-thermal catalytic reactor for the reverse water gas shift reaction under concentrated irradiation

An upscaled photo-thermal catalytic reactor for the heterogeneously catalysed reverse Water Gas Shift (rWGS) reaction is tested under simulated concentrated irradiation. The reactor is equipped with an aperture of 144 cm2 area covered by a quartz window, where it receives irradiation flux densities of up to 80 kW/m2 corresponding to an irradiation power input of 1 kW thereby directly irradiating a RuO2 based photo-thermal catalyst that is deposited on a porous support. The system was operated under simulated concentrated sunlight for a total of 45.5 h with 35.4 h of chemical operation. A peak CO production rate of 1.6 mol/h was achieved with an average light concentration factor of 80 in the centre of the catalyst layer. This corresponds to a solar-to-chemical efficiency – defined by the ratio of the product of molar CO production rate and reaction enthalpy for the rWGS reaction and the irradiation power input – of 1.69 %. A calculation approach to determine the catalyst surface temperature under irradiation was introduced and utilised for performance analysis leading to the discussion of design modifications and operating strategies towards performance enhancement.

Diarylformamides as a safe reservoir and room temperature source of ultra-pure CO for a 'green' rWGS reaction.

Diarylformamides are shown to be a safe reservoir and source of CO. Perfectly selective decarbonylation is achieved in solution at room temperature with potassium and cesium diarylamide catalysts. Moreover,solvent-freedecarbonylations may be run either in a diphenylformamide melt at 70 ºC or, when the bisformamide9is used, in thesolid stateat 88 ºC in virtue of its improved atom economy. These These simple and practicaltransition-metal-freereactions afford ultra-pure (i.e.dry and solvent-free) CO at moderate temperatures and the byproduct diarylamines are recycled as pure compounds. In the absence of catalysts, diarylformamides1and9are long-term stable at > 200 ºC.DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph2NC(O)H and a barrier-free CO elimination from Ph2NC(O)-.

Core–Shell catalyst particles for tandem catalysis: An experimental/numerical approach towards optimal design

Tandem catalysis is a promising approach to intensify chemical processes and increase their efficiency. On the other hand, the design of efficient, optimal and targeted tailored tandem catalysts is yet so challenging as the optimal catalyst loading is difficult to assess a priori. In this article, we present a concise route towards the design of optimal core–shell tandem catalyst particles on the example of coupled RWGS and FTS reactions for any specific spherical morphology. The route features five consecutive steps including: tandem system identification, catalyst synthesis, i.e. mono- and tandem-functional, catalyst characterization and initial performance test, kinetic modeling with parameter estimation if necessary, and optimal design of catalysts. The initial step features thermodynamic equilibrium calculations for RWGS and FTS showing a common operational window. Then, Pt and Co are selected as active metals and the formulation of the tandem catalyst is designed. For the second step, the synthesis route for the tandem catalyst Pt,CeO2@SiO2-Co, and the mono-functional catalysts, Pt@SiO2 and CeO2@SiO2-Co are presented. For the third step, all catalysts were tested for CO2 hydrogenation as an exemplary tandem process. A reduced transport model from literature was adjusted for RWGS and FTS reactions with kinetic expression from literature to enable numerical optimization. The kinetic parameters are estimated based on the performance tests of the mono-functional reference materials, i.e. Pt@SiO2 for RWGS and CeO2@SiO2-Co for FTS. The model is validated by cross comparison to the data from the tandem reaction setup. In the fifth step, the model was used for the numerical optimization of the catalyst loading on core and shell leading to the identification of the optimal design, resulting in a significant increase of C2+ Yield.

Selectivity control between reverse water-gas shift and fischer-tropsch synthesis in carbon-supported iron-based catalysts for CO2 hydrogenation

CO2 hydrogenation to chemicals and fuels has the potential to alleviate CO2 emissions and displace fossil resources simultaneously via consecutive RWGS and FTS reactions, also known as CO2-FTS. As Fe-based catalysts are active and selective for both reactions, their bifunctionality requires a delicate balance between the RWGS and FTS. In this work, we investigated the thermodynamic constraints of RWGS and CO2-FTS, the influence of CO2 conversion on selectivity and the influence of Fe nanoparticle size within the range of 4.7 to 10.3 nm. An inert carbon support was selected to rule out metal-support interaction and promoting effects of the support. Catalytic performance was evaluated at 300 °C, 11 bar, H2/CO2/Ar = 3/1/1, 600 to 72000 mL·gcat-1·h-1. At a CO2 conversion level below RWGS equilibrium conversion of 23 %, RWGS was found to be the primary and dominant reaction. No primary Sabatier reaction was observed. At higher CO2 conversion till the CO2-FTS threshold of 42 %, the secondary FTS reaction became dominant. Notably, a non-linear relation between CO2 conversion and CO selectivity was discovered. Comparing two catalysts with identical 5 wt% Fe loading but different average Fe nanoparticle size (6.6 and 8.4 nm), the 8.4 nm Fe catalyst was at least two times more active than the 6.6 nm Fe catalyst. In situ Mössbauer spectroscopy suggested a positive correlation between particle size, carburization and selectivity towards long-chain hydrocarbons. For these potassium-promoted carbon-supported Fe-based catalysts, nanoparticles of at least 8 nm are required for the formation of Fe carbides and improved reactivity.

Integrated CO2 capture and conversion by Cu/CaO dual function materials: Effect of in-situ conversion on the sintering of CaO and its CO2 capture performance

The integrated carbon capture and utilization (ICCU) technology has been considered a prospective strategy for mitigating carbon emissions issues. Compared to conventional CO2 capture and utilization, the ICCU process reduces transporting, product purification, construction, and operation costs. However, few works focus on investigating the effect of in-situ CO2 conversion on the sintering of CaO at high temperatures. In this work, Cu/CaO dual functional materials (DFMs) were synthesized and used in the Calcium Looping-Reverse Water-Gas Shift (CaL-RWGS) process at 650 °C. The results showed that it is thermodynamically feasible to couple the CaL with the RWGS reaction. In the cyclic CO2 capture test, Ca1Cu0.1 DFMs showed desirable CO2 capture performance (11.34 mmol/gDFMs) and self-activated phenomenon in the first 15 cycles. Moreover, Cu nanoparticle catalysts in the DFMs effectively inhibited the sintering of CaO by accelerating the desorption of CO2 from the CaO surface and converting it to CO during the conversion stage. In-situ DRIFTS of Ca1Cu0.1 DFMs revealed that formates might be the RWGS intermediates in CaL-RWGS.

Transforming CO2 to valuable feedstocks: Emerging catalytic and technological advances for the reverse water gas shift reaction

Current conditions suggest that to mitigate climate change, carbon neutrality must be achieved. Despite efforts to reduce carbon dioxide emissions, existing strategies remain inadequate. Thus, it is inevitable that carbon dioxide utilization will play a crucial role in the fight against climate change. Among the conversion routes available, the reverse water–gas shift reaction (RWGS) is promising as it allows the conversion of CO2 to CO, which can then be further converted to other valuable feedstocks while utilizing renewable H2. However, this route presents several challenges, as the RWGS reaction requires high energy input and is less favored over the methanation reaction at lower temperatures. Hence, the development of novel catalysts and advanced technologies is necessary to achieve high conversions and selectivity. This review summarizes the most recent progress and advances in heterogenous catalyst systems and emerging technologies explored for the RWGS reaction. Techniques to enhance catalyst performance, alter reaction mechanisms, and improve catalyst stability are discussed. Novel technologies and their recent developments to achieve equilibrium conversions and improve CO yield are also given focus and compared. This review thus provides insight into the possibilities available for improving the RWGS reaction as a practical carbon mitigation route.

Coupling and electronic synergistic effects of Fe/CeO2 composite to achieve high efficiency and selectivity for RWGS reaction

Transition metal iron, because of its high oxygen mobility, excellent thermal stability and low price, is often used in the study of RWGS reaction. However, the bottleneck problem of iron-based catalysts is the poor CO2 conversion rate. Herein, the Fe/CeO2 composite catalyst with Fe-O-Ce was successfully constructed, which has both high CO2 conversion and high CO selectivity for the low-temperature RWGS reaction. Furthermore, the influence of Fe0 contents is studied, and the result indicated that the CO2 conversion rate and CO selectivity are up to 50.05% and 100% at 500 ºC by the use of 20Fe/CeO2. Moreover, CeO2 is the best catalyst holder than the others. The physical and chemical properties of the catalysts are investigated by in-situ XPS, XRD, low-temperature N2 absorption-desorption (BET) and CO2-TPD. Nano zero-valent iron (Fe0) is the main active center for the RWGS reaction, which easily releases the outer electrons to activate reactant molecules. The introduction of the CeO2 is conducive to the high dispersion of Fe0 nanoparticles and the formation of abundant active centers. With the increase of Fe loading, the electron-rich Fe0 induces a strong electronic effect on the electron-deficient CeO2. The regularity of catalyst are changed by a large amount of zero-valent iron entering into the CeO2 lattice, then formed a lot of Fe-O-Ce solid solution. A large amount of zero-valent iron enter into the CeO2 lattice, inhibiting the grain growth and aggregation of monometallic species, and promoting nano Fe species highly dispersed on CeO2 carriers, leading more active centers exposure. Meanwhile, the abundant oxygen vacancy on xFe/CeO2 surface is advantage for the adsorption and activation of H2 and CO2 molecules. Therefore, the coupling and electronic synergistic effects of the active component Fe0 and the carrier CeO2 make xFe/CeO2 becoming a promising candidate catalyst for RWGS reaction.

A 3D-printed CuNi alloy catalyst with a triply periodic minimal surface for the reverse water-gas shift reaction

A monolithic CuNi alloy catalyst with a typical triply periodic minimal surface, which is fabricated using 3D printing technology, exhibits significantly enhanced mass and heat transfer as well as exceptional stability towards the RWGS reaction.

Non-oxidative calcination enhances the methane dry reforming performance of Ni/CeO2−x catalysts under thermal and photo-thermal conditions

Calcination in hydrogen or argon improved nickel dispersion and increased the abundance of oxygen vacancies in ceria nanorods. Visible light both accelerated the methane reforming rate and improved H2 selectivity by retarding the RWGS reaction.

Engineering Pt–CeO2interfaces for reverse water-gas shift (RWGS) reaction

Pt–CeO2interfaces with superhydrophobic and highly reducible CeO2are designed with improved properties for the RWGS reaction.

Stabilized inverse Y2O3/Cu interfaces boost the performance of the reverse water–gas shift reaction

Sintered Cu species are applied to fabricate an inverse Y2O3/Cu catalyst with notable RWGS reaction performance. Inverse Y2O3/CuOx/Cu interfaces promote the metal–support interaction in the Y2O3/Cu catalyst to achieve excellent catalytic stability.

Ternary Fe- or Mo-Au-Ni/GDC as Candidate Fuel Electrodes for the Internal Dry Reforming of CH4: Physicochemical and Kinetic Investigation

The present study deals with the physicochemical and catalytic/kinetic investigation of Fe, Au, Fe-Au, and Mo-Au modified Ni/GDC electrocatalysts towards their performance for the DRM, RWGS, and CH4 decomposition reactions. For this purpose, Au-NiO/GDC (where Au = 1 or 3 wt.%), Fe-NiO/GDC (where Fe = 0.5 or 2 wt.%), 0.5Fe-3Au-NiO/GDC, and 0.4Mo-3Au-NiO/GDC were synthesized via deposition (co-) precipitation. There is discussion on the structural properties of the electrocatalysts on the oxidized and reduced state, as well as their use as electrolyte-supported (half) cells. A key remark after H2-reduction is the formation of binary or ternary solid solutions. Ni/GDC was the most active for the catalytic CO2 reforming of CH4 and the CH4 decomposition reactions and as a result the most prone to carbon deposition. On the other hand, the modified 3Au-Ni/GDC, 0.5Fe-3Au-Ni/GDC, and 0.4Mo-3Au-Ni/GDC exhibited the following properties: (i) the highest Ea,app for the non-desired RWGS reaction, (ii) high tolerance to carbon formation due to lower activity for the CH4 decomposition, and (iii) were also less active for H2 and CO production. Finally, 0.4Mo-3Au-Ni/GDC seems to perform the DRM reaction through a different mechanism when compared to Ni/GDC. Overall, the above three samples are proposed as potential fuel electrodes for further electrocatalytic measurements for the SOFC internal DRM process.

Small Cobalt Nanoparticles Favor Reverse Water‐Gas Shift Reaction Over Methanation Under CO2 Hydrogenation Conditions**

AbstractCobalt‐based catalysts are well‐known to convert syngas into a variety of Fischer–Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO2 hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co‐NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC‐derived Co‐NPs display significantly different catalytic performances under CO2 hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water‐gas shift (rWGS) reaction, the larger nanoparticles (2.1–3.0 nm) favor the expected methanation activity. Operando X‐ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO2 hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water‐gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO2 hydrogenation conditions.

Small Cobalt Nanoparticles Favor Reverse Water-Gas Shift Reaction Over Methanation Under CO2 Hydrogenation Conditions.

Cobalt-based catalysts are well-known to convert syngas into a variety of Fischer-Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO2 hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co-NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC-derived Co-NPs display significantly different catalytic performances under CO2 hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water-gas shift (rWGS) reaction, the larger nanoparticles (2.1-3.0 nm) favor the expected methanation activity. Operando X-ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO2 hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water-gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO2 hydrogenation conditions.