Synthetic natural gas (SNG) can be obtained via methanation of synthesis gas (syngas). Many thermodynamic reaction details involved in this process are not yet fully understood. In this paper, a comprehensive thermodynamic analysis of reactions occurring in the methanation of carbon oxides (CO and CO2) is conducted using the Gibbs free energy minimization method. The equilibrium constants of eight reactions involved in the methanation reactions were calculated at different temperatures. The effects of temperature, pressure, ratio of H-2/CO (and H-2/CO2), and the addition of other compounds (H2O, O-2, CH4, and C2H4) in the feed gas (syngas) on the conversion of CO and CO2, CH4 selectivity and yield, as well as carbon deposition, were carefully investigated. In addition, experimental data obtained on commercial Ni-based catalysts for CO methanation and three cases adopted from the literature were compared with the thermodynamic calculations. It is found that low temperature, high pressure, and a large H-2/CO (and H-2/CO2) ratio are favourable for the methanation reactions. Adding steam into the feed gas could alleviate the carbon deposition to a large extent. Trace amounts of O-2 in syngas is unfavourable for SNG generation although it can lower carbon deposition. Additional CH4 in the feed gas almost has no influence on the CO conversion and CH4 yield, but it leads to the increase of carbon formed. Introduction of a small amount of C2H4, a representative of hydrocarbons in syngas, results in low CH4 yield and serious carbon deposition although it does not affect CO conversion. CO is relatively easy to hydrogenated compared to CO2 at the same reaction conditions. The comparison of thermodynamic calculations with experimental results demonstrated that the Gibbs free energy minimization method is significantly effective for understanding the reactions occurring in methanation and helpful for the development of catalysts and processes for the production of SNG.

A thermodynamic analysis of methanation reactions of carbon oxides for the production of synthetic natural gas

CO2 methanation over heterogeneous catalysts: recent progress and future prospects

Recent progress in selective CO removal in a H2-rich stream

Mesostructured silica nanoparticles (MSN) and Ni loaded onto MSN (Ni/MSN) for the methanation of CO2 were prepared by the sol–gel and impregnation methods. Catalytic testing was conducted in the temperature range of 423–723 K under atmospheric pressure in the presence of H2. Ni supported on MSN was compared with others types of support such as MCM-41 (Mobile Crystalline Material), HY (protonated Y zeolite), SiO2 and γ-Al2O3. The activity of CO2 methanation followed the order: Ni/MSN > Ni/MCM-41 > Ni/HY > Ni/SiO2 > Ni/γ-Al2O3. The nitrogen physisorption and pyrrole adsorbed IR spectroscopy results indicated that the high activity of Ni/MSN is due to the presence of both intra- and inter-particle porosity which led to the high concentration of basic sites. In addition, the correlation between N–H band intensity and the turnover frequency revealed that the methanation activity increased with increasing of the concentration of basic sites. The presence of defect sites or oxygen vacancies in MSN was responsible for the formation of surface carbon species, while Ni sites dissociated hydrogen to form atomic hydrogen. The surface carbon species then interacted with atomic hydrogen to form methane. The Ni/MSN catalyst performed with good stability and no deactivation up to 200 h.

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Highly active Ni-promoted mesostructured silica nanoparticles for CO2 methanation

Preferential oxidation of CO (PROX) is an important reaction for removing small amounts of CO to a parts-per-million level from the hydrogen-rich stream, which will be ultimately supplied as a fuel to polymer–electrolyte membrane fuel cells. The key to the application of PROX is to develop a highly active and selective catalyst that operates well in a wide temperature window (e.g., 80–180 °C) and has good resistance to CO2 and steam. In the past decades, various catalyst formulations have been developed, among which platinum group metal catalysts, including Pt, Ru, and Ir—in particular, those modified with promoters such as alkali metals and reducible metal oxides—have received a great deal of attention for their significantly improved catalytic activities in the low-temperature range. In this minireview, the recent advances of the platinum group metal catalysts for the PROX reaction are summarized, including performances of unpromoted and promoted catalysts, reaction mechanisms, and kinetics. In addition...

Recent Advances in Preferential Oxidation of CO Reaction over Platinum Group Metal Catalysts

Hydrodynamics and solid-liquid contacting effectiveness in trickle-bed reactors

Open issues in oxidative catalysis for diesel particulate abatement

Abstract Selective CO methanation (CO-SMET) as a strategy for complete CO removal in fuel processing applications was investigated over Ru-based catalysts. The CO-SMET, in fact, seems to be a good alternative to the CO preferential oxidation (CO-PROX) for the applications on polymer electrolyte membrane fuel cells (PEM FCs) to transportation vehicles, boats, yachts and residential co-generators, as a CO-SMET reactor is inherently easier to control than the CO-PROX one. The present paper deals with the study on complete removal of CO in H 2 -rich gas stream through CO-SMET over Ru-based catalysts supported on γAl 2 O 3 carrier. All the catalysts, loaded with 3%, 4% and 5% Ru, respectively, were prepared by a conventional impregnation method and their CO removal performance was determined at the powder level in a fixed bed reactor. Starting from a synthetic reformate mixture of 0.5% CO, 40% H 2 , 18% CO 2 , 15% H 2 O in He, the obtained results showed that CO complete conversion (residual outlet concentration lower than 2 ppmv, the analytical detection limit) was reached in a suitable temperature range where simultaneously both the CO 2 methanation was kept at a low level and the reverse water gas shift reaction was negligible. The best results were obtained with 4% Ru–γAl 2 O 3 in the range of 300–340 °C.

CO-selective methanation over Ru-Al2O3 catalysts in H2-rich gas for PEM FC applications

Even traces of CO in the hydrogen-rich feed gas to proton exchange membrane fuel cells (PEMFC) poison the platinum anode electrode and dramatically decrease the power output. In this work, a variety of catalytic materials consisting of noble metals supported on A zeolites were synthesised, characterised and tested under realistic conditions in the quest of a catalyst for the removal of CO via the CO preferential oxidation (CO-PROX) reaction. Pt, Pd and Ru-based catalysts, prepared by wet impregnation and characterised by XRD and HRTEM, were investigated in a fixed bed reactor, by determining CO conversion and selectivity through the outlet concentrations of CO and O2. In contrast to supported Pd and Ru catalysts, Pt-catalysts showed complete CO-conversion and a comparatively high selectivity. The 1% Pt-3A catalyst showed the best performance: it kept the complete CO-conversion in a wide temperature range, showing the highest selectivity for CO oxidation with minimal involvement in side reactions, such as H2 oxidation and RWGS reaction. Experimental data proved that the RWGS outcome is directly related to the support structure. The rather high temperature (≈260 °C) at which complete CO conversion is achieved by the 1% Pt-3A catalyst enables to locate the CO-PROX unit immediately after the low temperature water-gas shift unit of the fuel processor converting hydrocarbons into hydrogen-rich gas.

Vito Specchia

Papers

Hydrodynamics and solid-liquid contacting effectiveness in trickle-bed reactors

Open issues in oxidative catalysis for diesel particulate abatement

CO-selective methanation over Ru-Al2O3 catalysts in H2-rich gas for PEM FC applications

Development of A zeolites-supported noble-metal catalysts for CO preferential oxidation: H2 gas purification for fuel cell

Development of A zeolites-supported noble-metal catalysts for CO preferential oxidation: H2 gas purification for fuel cell