Molecular transition metal corrole as an efficient electrocatalyst for the heterogeneous CO2 electroreduction: A theory study

Carbon dioxide electrochemical reduction (eCO₂RR) has been regarded as an important solution for low-carbon economy. However, challenges remain for searching low-cost and high selectivity catalysts. Here, we investigated electrocatalytic activity of molecular catalysts containing transition metal single atom supported on corrole as the eCO₂RR catalysts (TM/SACC) by DFT. Various C₁ products can be produced on the 14 TM/SACC, including methane (CH₄), formic acid (HCOOH) and CO. We found CO and formic acid are major products on TM/SACC (TM = Ni, Pd, Zn, Cu, Au, Ag) at higher overpotentials, while methane are major eCO₂RR products on TM/SACC (TM = Mn, Cr, Nb, Mo, Zr, V, Ti, Cd) at lower overpotentials. Our studies indicate Mn/SACC gives high selectivity for methane formation. Due to the lowest overpotential value of 0.46 V, Mn/SACC can be a quite promising catalyst with excellent performance for reduction of CO₂ to methane along the most favorable pathway: CO₂ → COOH1 → CO1 → CHO1 → CH₂O1 → CH₂OH1 → CH₃OH1→CH₃1→CH₄1→CH₄(g), among which the hydrogenation of CHO1 to CH₂O1 and CH₃OH1 to CH₃1 and H₂O are the limiting-potential step and rate-determining step, respectively. The study shows corrole with different transition metal could adjust the catalytic performance of electrocatalysts, which offer a hopeful strategy for the design of molecular catalysts.     

Insight into the mechanism of ethanol steam reforming on TM/Mo6S8 clusters catalysts: A theoretical investigation

Density functional theory (DFT) calculations were carried out to investigate the reaction mechanism of ethanol steam reforming (ESR) reaction on TM/Mo₆S₈ (TM = Rh, Ir) clusters. We investigated the reaction mechanism of TM/Mo₆S₈ catalyzed ESR by studying the cleavage of C–H, C–C, and O–H bonds and the formation of hydrogen, and explored the catalytic activity of TM/Mo₆S₈ in order to find superior catalyst. Our results indicate that ESR is first decomposed by ethanol and then subjected to water-gas shift (WGS) reaction to produce H₂ and CO₂. In addition, we found that the formation of CH₄ and CO is favored as the products of ethanol decomposition, the O–H bond cleavage of OH* is considered as the key step in ESR. According to our calculations, we found that Ir/Mo₆S₈ was more favorable for catalyzing ethanol decomposition and Rh/Mo₆S₈ was beneficial for catalyzing WGS. However, for the whole reaction, Rh/Mo₆S₈ exhibits better catalytic performance than Ir/Mo₆S₈ because of low energy barrier of rate-determining step. A comparison of microkinetic modeling, the metals d-band and projected density of state (DOS) show that Rh/Mo₆S₈ is superior catalyst. This approach provides theoretical insight into the reaction mechanism for suppressing the carbon formation on TM/Mo₆S₈ (TM = Rh, Ir) and is expected to have a significant implication on general methods of the ESR catalyst design in order to have better activity and stability.     

Combined dry reforming and partial oxidation of methane to synthesis gas on noble metal catalysts

In this paper CO₂ reforming of methane combined with partial oxidation of methane to syngas over noble metal catalysts (Rh, Ru, Pt, Pd, Ir) supported on alumina-stabilized magnesia has been studied. The catalysts were characterized by using BET, XRD, SEM, TEM, TPR, TPH and H₂S chemisorption techniques. The H₂S chemisorption analysis showed an active metal crystallite size in the range of 1.8-4.24 nm for the prepared catalysts. The obtained results revealed that the Rh and Ru catalysts showed the highest activity in combined reforming and both the dry reforming and partial oxidation of methane. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50 h of reaction. In addition, the H₂/CO ratio was around 2 and 0.7 over different catalysts for catalytic partial oxidation and dry reforming, respectively.     

Assessment of coal and graphite electrolysis on carbon fiber electrodes

Novel carbon fiber electrodes prepared by plating of noble metals (Pt, Rh, Pt–Rh, Pt–Ir, Pt–Ir–Rh) on carbon fibers were evaluated for the electrolysis of coal and graphite under galvanostatic conditions. Graphite was used as a baseline to compare its performance with coal. The electrodes were tested on a sandwich configuration coal electrolytic cell (CEC) designed to reduce the ohmic resistance of the system. Among Pt, Rh, Pt–Rh, Pt–Ir, and Pt–Ir–Rh electrodes with the same loading (5 mg cm⁻¹ of fiber bundle), Pt and Pt–Ir seemed to produce the highest CO₂ Faradaic efficiency. Factorial design was used to determine the effect of loading and composition on the electrooxidation of coal and graphite to CO₂. The effect of abrasion on the coating of the electrodes was determined by performing weight change analysis. Most electrodes were not significantly affected by abrasive effect (about 2% weight loss); however, Pt and Pt–Rh electrodes were significantly affected by erosion (above 10% weight loss). The presence of graphite had a positive effect on the electrooxidation of coal to CO₂ in a graphite–coal slurry mixture. The energy consumption for the production of hydrogen from the electrolysis of coal was about 22 Wh g⁻¹ of H₂ for all the electrodes tested (50% lower than that for hydrogen production by electrolysis of water under similar operating conditions). This fact shows that coal electrolysis is a competitive method for in situ hydrogen generation.     

IrRuOx/TiO2 a stable electrocatalyst for the oxygen evolution reaction in acidic media

Proton Exchange Membrane Electrolysis of Water (PEMWE) stands out as a scalable, CO₂-free process to produce H₂ for energy delivery and industrial applications. Due to the limited Ir and Ru worldwide availability, one of the main challenges for the GW-scale PEMWE implementation is the loading reduction of these metals in the anodic catalytic layer. Here, Ir–Ru loading (5 wt%Ir-40 wt%Ru) was deposited through their impregnation over TiO₂, followed by a thermal-oxidative treatment, obtaining IrRuO_x/TiO₂ catalyst. SEM-EDS and HR-TEM confirmed the homogeneous dispersion of IrRuO_x on TiO₂. The supported catalyst showed a 1.4-fold higher mass activity (85 mA/mg Ir–Ru) for the oxygen evolution reaction (OER) than a mechanical mixture of IrO₂–RuO₂ 1:3 (54 mA/mg_Ir+Ru) in H₂SO₄ 0.5 M, at 1.52 V/RHE. Furthermore, the supported catalyst retains 90% of its catalytic activity after 100 reaction cycles suggesting the RuO₂ intermediate species stabilization by IrO_x, which can avoid its irreversibly transform into hydrous RuO_x.     

H2 evolution by water SPLITTING on Rh/La2O3

The physicochemical and electrochemical properties of rhodium catalysts supported on La₂O₃ denoted XRhLa (X = 1 and 5% wt. Rh) prepared by impregnation using RhCl₆H₂O as precursor salt were studied. The solids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal analysis (TG/TDA) and hydrogen chemisorption (HC) to evaluate the dispersion of the metal phase. The temperature-programmed reaction with hydrogen (H₂-TPR), carbon monoxide (CO-TPR) or methane (CH₄-TPR) were carried out to elucidate there effects on catalytic reaction. The adsorption and decomposition of H₂O has been investigated on the surface catalysts. The number of reduced centers of lanthanum in Rh/La₂O₃ catalysts was measured by in situ oxidation of these centers at oxydation temperature of water (T_OXtov) by water pulses according to the following reaction (Reduced centers + H₂O→Oxidized center + H₂). The amount of hydrogen Q(H), evolved in the reaction allows us to calculate the number of reduced centers of the support since the Rh metal is not oxidized. The results showed that although the conversion rate of water to H₂ is low, the 5% wt. Rh catalyst is a promising candidate in the water adsorption and dissociation compared to the 1% wt.     

Single transition metal atom catalysts on Ti2CN2 for efficient CO2 reduction reaction

Electrochemical CO₂ reduction reaction (CO₂RR) is an efficient way in the utilization of CO₂. In this work, single transition-metal (TM) atom (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) anchored on two-dimensional (2D) Ti₂CN₂ are designed for CO₂RR using density-functional-theory (DFT) calculation. We show that Ti₂CN₂ serves as an excellent substrate to support single atom catalysts (SACs), compared to Ti₂CO₂ and Ti₂CF₂. We find that the Sc, Ti and V supported on Ti₂CN₂ show high catalytic activities to produce CO with a low overpotential of 0.37, 0.27, and 0.23 eV, respectively. Differently, the Mn and Fe on Ti₂CN₂ are catalytically active for the production of HCOOH with a low overpotential of 0.32 and 0.43 eV, respectively. We further show that the negatively charged TM-Ti₂CN₂ can capture and activate CO₂ more effectively, and the catalytic activity and selectivity can be significantly tuned by injecting extra electrons.     

Simultaneous production of H2 and C2 hydrocarbons by using a novel configuration solid-electrolyte + fixed bed reactor

A novel combined single chamber solid electrolyte plus fixed bed reactor configuration was developed for the simultaneous production of H₂ and C₂ hydrocarbons from a humidified CH₄ atmosphere. Hence, a Pt/YSZ/Ag solid electrolyte cell was placed on the top of an active oxidative coupling catalyst powder bed Ce–Na₂WO₄/SiO₂. H₂ was produced via steam electrolysis in a Pt cathode of the solid electrolyte cell (H₂O + 2e⁻ → H₂ + O²⁻). Simultaneously, the produced O²⁻ ions were electrochemically pumped to the Ag anode, leading to the C_2s production, via oxidative coupling of CH₄ (4CH₄ + 3O²⁻ → C₂H₄ + C₂H₆ + 3H₂O + 6e⁻). Additionally, non-reacted O²⁻ molecules desorbed to the gas phase (2O²⁻ → O₂+4e⁻) and reacted with CH₄ in the catalyst bed leading to an increase of C_2s yield. The influence of different reaction parameters was investigated together with long-term reaction experiments, confirming the stability of this configuration for its practical application. The obtained results demonstrated that the addition of an active catalyst bed strongly enhances both: the efficiency of the single chamber steam electrolysis and the oxidative coupling process.     

An alkaline direct NaBH4–H2O2 fuel cell with high power density

A high performance alkaline direct borohydride–hydrogen peroxide fuel cell with Pt–Ru catalyzed nickel foam as anode and Pd–Ir catalyzed nickel foam as cathode is reported. The electrodes were prepared by electrodeposition of the catalyst components on nickel foam. Their morphology and composition were analyzed by SEM–EDX. The effects of concentrations of NaBH₄ and H₂O₂ as well as operation temperature on the cell performance were investigated. The cell exhibited an open circuit voltage of about 1.0 V and a peak power density of 198 mW cm⁻² at a current density of 397 mA cm⁻² and a cell voltage of 0.5 V using 0.2 mol dm⁻³ NaBH₄ as fuel and 0.4 mol dm⁻³ H₂O₂ as oxidant operating at room temperature. Electrooxidation of NaBH₄ on Pt–Ru nanoparticles was studied using a rotating disk electrode and complete 8e⁻ oxidation was observed in 2 mol dm⁻³ NaOH solution containing 0.01 mol dm⁻³ NaBH₄.     

High selective and efficient Fe2–N6 sites for CO2 electroreduction: A theoretical investigation

Developing high efficient and cheap electrocatalysts for carbon dioxide reduction reaction (CO₂RR) is the key to achieve CO₂ transformation into clean energy. Herein, a series of transition metal dimer and nitrogen codoped graphene (M₂N₆-Gra, M = Cr–Cu) acting as electrocatalysts for CO₂RR are investigated based on the density functional method. For M₂N₆-Gra (M = Cr, Mn), the selectivity is poor and CO poisoning is serious. Fe₂N₆-Gra is the best CO₂RR catalyst due to the good selectivity and catalytic activity. The calculated overpotential is very small, i.e., 0.03 V for COOH channel, 0.05 V for HCOO channel. Hydrogen evolution reaction is also refrained on the Fe₂N₆-Gra surface, which further supports its high catalytic performance. For M₂N₆-Gra (M = Co, Ni, Cu), the catalytic activity is poor due to large overpotentials. These results indicate that if designed carefully, the transition metal dimer and nitrogen codoped graphene would be good candidate for the high efficient and selective CO₂RR catalyst.     

Enhanced alkaline water splitting on cobalt phosphide sites by 4d metal (Rh)-doping method

The construction of effective water-splitting electrocatalysts in alkaline conditions is challenging due to lower water dissociation efficiency than in acidic conditions. In this study, we investigated the effect of doping 4d and 5d metals into the 3d metal active site of cobalt phosphide (Co_xP) on the water-splitting reaction. Introducing Ru slightly improved hydrogen evolution efficiency, but Rh doping significantly enhanced the catalytic parameters with an overpotential of 0.03 V at 10 mA/cm². Rh regulated the electronic structure of Co_xP to improve proton reduction. The Rh-Co_xP electrode showed a comparable catalytic efficiency to that of a Pt/C standard. Ir doping slightly improved catalytic reactivity, but not as much as Rh. Our results showed that doping 4d metal from the same group as Co maximizes the doping effect during hydrogen evolution. A lab-scale water electrolyzer built with Rh-Co_xP successfully demonstrated catalytic water splitting in alkaline electrolyte.     

Hydrogen production from an ethanol reformer with energy saving approaches over various catalysts

The reforming of ethanol for hydrogen production was carried out in this study. The effects of ethanol supply rate, catalysts, O₂/EtOH and different energy-saving approaches on the reforming temperature, H₂ + CO (syngas) concentration and thermal efficiency were investigated. The results showed that the best H₂ + CO concentration of 43.41% could be achieved by using rhodium (Rh), while the next best concentration of about 42.08% could be obtained using ruthenium (Ru). The results also showed that the conversion efficiency of ethanol, concentrations of H₂ and CO, and the energy loss ratio could be improved by heat insulation and heat recycling; and the improvement in the reforming performance was greater by the Ru catalyst rather than by the Rh catalyst with the energy-saving approaches. The greatest improvement in hydrogen production was achieved when using the Ru catalyst with the addition of steam and heat recycling system under an O₂/EtOH ratio of 0.625 and S/C ratio of 1.0.     

Ultrafine Ru nanoparticles derived from few-layered Ti3C2Tx MXene templated MOF for highly efficient alkaline hydrogen evolution

It is meaningful to search high-efficient and inexpensive electrocatalysts for hydrogen evolution reaction (HER) due to the energy crisis and environmental pollution. Here, we report the preparation of ultrafine Ru nanoparticles from a hybrid of ZIF-L(Co) MOF and polydopamine coated few-layered Ti₃C₂T_x MXene (FL-Ti₃C₂T_x). FL-Ti₃C₂T_x is used as a template to grow regular leaf-shaped ZIF-L(Co) nanosheets through the reaction of Co ions anchored on the MXene surface with 2-methylimidazole. The obtained hybrid is then doped with Ru ions through ion exchange between Ru and Co ions, followed by thermal annealing at a temperature of 350 °C in an Ar atmosphere to produce ultrafine Ru nanoparticles. The obtained Ru@ZIF-L(Co)/FL-Ti₃C₂T_x nanocomposite shows outstanding HER performance with a low overpotential of 16.2 mV at a current density of 10 mA cm^?2, a small Tafel slope of 21.0 mV dec^?1 and excellent stability in 1.0 M KOH solution. This work provides a new strategy for the design and synthesis of highly efficient HER catalyst via MOFs with tunable composition and structure.     

Catalysts for H2 production using the ethanol steam reforming (a review)

This review aims to provide an overview of the main catalytic studies of H₂ production by ethanol steam reforming (ESR). The reaction is endothermic and produces H₂, CO₂, CH₄, CO and coke. The conversion and H₂ selectivity of these products depended greatly of the physicochemical properties of the catalysts, active metal, promoters, temperature, long-term reaction, water/ethanol ratio, space velocity, contact time, and presence of O₂. Initial total conversion has been reported in all catalysts evaluated between 300 and 850 °C. The noble catalysts with high selectivity to H₂ (more than 80%) were: Rh, Ru, Pd and Ir and non-noble metal catalysts were: Ni, Co and Cu. The support materials include CeO₂, ZnO, MgO, Al₂O₃, zeolites-Y, TiO₂, SiO₂, La₂O₂CO₃, CeO₂–ZrO₂ and hydrotalcites. The impregnation method produced the best noble metal catalysts in terms of selectivity and conversion. The decrease of coke was related with the presence of basic sites on the support.     

Metal foam-supported Pd–Rh catalyst for steam methane reforming and its application to SOFC fuel processing

Pd–Rh/metal foam catalyst was studied for steam methane reforming and application to SOFC fuel processing. Performance of 0.068 wt% Pd–Rh/metal foam catalyst was compared with 13 wt% Ni/Al₂O₃ and 8 wt% Ru/Al₂O₃ catalysts in a tubular reactor. At 1023 K with GHSV 2000 h⁻¹ and S/C ratio 2.5, CH₄ conversion and H₂ yield were 96.7% and 3.16 mol per mole of CH₄ input for Pd–Rh/metal foam, better than the alumina-supported catalysts. In 200 h stability test, Pd–Rh/metal foam catalyst exhibited steady activity. Pd–Rh/metal foam catalyst performed efficiently in a heat exchanger platform reactor to be used as prototype SOFC fuel processor: at 983 K with GHSV 1200 h⁻¹ and S/C ratio 2.5, CH₄ conversion was nearly the same as that in the tubular reactor, except for more H₂ and CO₂ yields. Used Pd–Rh/metal foam catalyst was characterized by SEM, TEM, BET and CO chemisorption measurements, which provided evidence for thermal stability of the catalyst.     

Photoelectrocatalytic reduction of CO2 to methanol over CuFe2O4@PANI photocathode

The present study was aimed to convert CO₂ into methanol which not only addresses the potential solution for controlling the CO₂ concentration level in the atmosphere but also offers an alternative approach for the production of renewable energy source. In this perspective, a hybrid photocatalyst, PANI@CuFe₂O₄ was synthesized, characterized and used as a photocathode for photoelectrocatalytic (PEC) reduction of CO₂ to methanol in aqueous medium at an applied potential of ?0.4 V vs NHE under visible light irradiation. The combination of PANI with CuFe₂O₄ greatly increased the PEC CO₂ reduction to methanol owing to enhance the CO₂ chemisorption capacity by the photocathode surface and at the same time facilitated the separation of photogenerated electron-hole (e^?/h⁺) pairs. The incident photon to current efficiency (IPCE) and quantum efficiency (QE) for methanol formation in PEC CO₂ reduction could be achieved as 7.1 and 24.0% respectively. The rate of formation of methanol in PEC CO₂ reduction was found as 49.3 μmol g^?1h^?1 with 73% Faradaic efficiency. Compared to photocatalytic reaction, the PEC results demonstrated that the applied potential could effectively separate the photogenerated e^?/h⁺ pairs and therefore, enhanced the PEC CO₂ reduction activity of the hybrid photocatalyst.     

Highly efficient photocatalytic hydrogen evolution by using Rh as co-catalyst in the Cu/TiO2 system

Cu/TiO₂ was modified by adding Rh as co-catalyst and used as a highly efficient photocatalyst for the hydrogen evolution reaction. A low amount of Rh was loaded onto Cu/TiO₂ by the deposition-precipitation with urea (DPU) method to observe the effect on the hydrogen production displayed by different samples. The Rh–Cu/TiO₂ oxide structure exhibited a remarkably high photocatalytic hydrogen evolution performance, which was about twofold higher than that of the Cu/TiO₂ monometallic photocatalyst. This outstanding performance was due to the efficient charge carrier transfer as well as to the delayed electron-hole recombination rate caused by the addition of Rh. The influence of the different parameters of the photocatalyst synthesis and reaction conditions on the photocatalytic activity was investigated in detail. Hydrogen evolution was studied using methanol, ethanol, 2-propanol and butanol as scavengers with an alcohol:water ratio of 20:80. The methanol-water system, which showed the highest hydrogen production, was studied under 254, 365 and 450 nm irradiation; Rh–Cu/TiO₂ showed high photocatalytic activity with H₂ production rates of 9260, 5500, and 1940 μmol h^?1 g^?1, respectively. The Cu–Rh/TiO₂ photocatalyst was active under visible light irritation due to its strong light absorption in the visible region, low band gap value and ability to reduce the electron (e^?) and hole (h⁺) recombination.     

Phosphatizing engineering of heterostructured Rh2P/Rh nanoparticles on doped graphene for efficient hydrogen evolution in alkaline and acidic media

A wide diversity of phosphides of platinum-group metal including Rh, Ru and Ir exhibit intriguing electrocatalytic activity toward hydrogen evolution reaction (HER). The phosphidation degree, namely the P dosage in these phosphides shows pronounced influence on the catalytic performance but is hard to control. In this work we developed a reliable strategy to synthesize Rh₂P-based nanoparticles with controlled phosphidation degree, and investigated the influence of phosphidation degree on HER. It is found that the heterostructured Rh₂P/Rh nanoparticle, i.e., the P-deficient composite with mixed metallic and phosphide phases, outperforms either the metallic Rh or pure Rh₂P nanoparticles. As-synthesized Rh₂P/Rh nanoparticles supported on P/N co-doped graphene (denoted as Rh₂P/Rh-G) display remarkable HER activity with tiny overpotential of 17 and 19 mV at 10 mA cm^?2 current density in alkaline and acid, efficiently surpassing its Rh-based rivals and benchmark Pt/C catalyst. Meanwhile it illustrates a large mass-specific activity (3.23 and 6.26 A mg^?1 @50 mV overpotential in alkaline and acid, respectively) due to its high activity and low metal loading. Density functional theory (DFT) calculation indicates that the Rh₂P/Rh heterostructured interface possesses the optimal close-to-zero value of hydrogen adsorption energy and water dissociation process is accelerated, and thus boosts HER activity.     

Enhancement of hydrogen adsorption by alkali-metal cation doping of metal-organic framework-5

Over the past decade, metal-organic frameworks (MOFs) have been extensively studied as a novel approach to store hydrogen. The large surface area and volume of micropores that are intrinsic to MOFs make them ideal for gas adsorption. In addition, we chemically reduced MOF-5 by doping it with alkali metals (Li, Na, and K). We found that the H₂ uptake capacity of MOF-5 materials doped with Li, Na, and K exceeded that of a neutral framework by 24%, 68%, and 70%, respectively. Notably, at the same levels of doping, the Li⁺-doped framework exhibited the strongest H₂ binding, and the binding strength decreased sequentially in the order Li⁺ > Na⁺ > K⁺.     

Utilization of CO2 for syngas production by CH4 partial oxidation using a catalytic membrane reactor

In this research, a synthetic flue gas mixture with added methane was used as the feed gas in the process of dry reforming with partial oxidation of methane using a laboratory scale catalytic membrane reactor to produce hydrogen and carbon monoxide that can present the starting point for methanol or ammonia synthesis and Fischer-Tropsch reactions. 0.5% wt% Rh catalyst was deposited on a γ-alumina support using rhodium (III) chloride precursor and incorporated into a shell and tube membrane reactor to measure the yield of synthesis gas (CO and H₂) and conversion of CH₄, O₂ and CO₂ respectively. These measurements were used to determine the reaction order and rate of CO₂. The conversion of CO₂ and CH₄ were determined at different gas hourly space velocities. The reaction order was determined to be a first-order with respect to CO₂. The rate of reaction for CO₂ was found to follow an Arrhenius equation having an activation energy of 49.88 × 10⁻¹ kJ mol⁻¹. Experiments were conducted at 2.5, 5 and 8 ml h⁻¹ g⁻¹ gas hourly space velocities and it was observed that increasing the hourly gas velocities resulted in a higher CO₂ and CH₄ conversions while O₂ conversion remained fairly constant. CO₂ had a high conversion rate of 96% at 8 ml h⁻¹ g⁻¹. The synthesized catalytic membrane was characterized by Scanning Electron Microscopy (SEM) and the Energy Dispersive X-ray Analysis (EDXA) respectively. The micrographs showed the Rh particles deposited on the alumina support. Single gas permeation of CH₄, CO₂ and H₂ through the alumina support showed that the permeance of H₂ increased as the pressure was increased to 1 × 10⁵ Pa. The order of gas permeance was H₂ (2.00 g/mol) > CH₄ (16.04 g/mol) > N₂ (28.01 g/mol) > O₂ (32 g/mol) > CO₂ (44.00 g/mol) which is indicative of Knudsen flow mechanism. The novelty of the work lies in the combination of exothermic partial oxidation and endothermic CO₂ and steam reforming in a single step in the membrane reactor to achieve near thermoneutrality while simultaneously consuming almost all the greenhouse gases in the feed gas stream.