Nickel catalysts supported on the perovskite oxide CaTiO3 (CTO) were prepared by an impregnation method for CO methanation to produce synthetic natural gas (SNG). X-Ray diffraction, nitrogen adsorption, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, H2-temperature programmed reduction and desorption, and X-Ray photoelectron spectroscopy were employed for the characterization of samples. The results revealed that the Ni/CTO catalysts showed a better performance than Ni/Al2O3 for CO methanation at various reaction conditions. The life time test at 600 °C and 3.0 MPa indicates that Ni/CTO is also more active, thermally stable and resistant to carbon deposition. This is because of the relatively weak Ni–CTO support interaction, highly stable CTO support, the absence of acidic sites on the surface of CTO and the proper Ni particle size of about 20–30 nm. The work is important for the development of effective methanation catalysts for SNG production.

A series of α-Al2O3-supported Ni catalysts with different Ni particle sizes (5–10, 10–20, and 20–35 nm) were prepared and applied in the CO methanation reaction for the production of synthetic natural gas (SNG). The catalytic tests showed that the Ni nanoparticles influenced the catalytic performance in the CO methanation, and the catalyst with a Ni nanoparticle size of 10–20 nm showed the highest CO conversion, CH4 yield, and turnover frequency, and the lowest carbon deposition, demonstrating the possibility of improving the Ni/α-Al2O3 catalysts in the CO methanation for SNG production by controlling their Ni particle size.

We report the simple preparation of the barium hexaaluminate (BaO·6Al2O3, BHA) with high surface area (BHA-HSA) (>100 m2 g−1) through a coprecipitation method using carbon black as the hard template. Ni catalysts supported on BHA-HSA (Ni/BHA-HSA) with different NiO loadings (10, 20, and 40 wt%) were investigated in CO methanation for the production of synthetic natural gas (SNG). The CO methanation reaction was carried out at 0.1 and 3.0 MPa with a weight hourly space velocity of 30000 mL g−1 h−1. It was found that Ni/BHA-HSA catalysts showed increased activity at low temperature (240–400 °C) compared with more conventional Ni/BHA catalysts with the same NiO loadings. A highest CH4 yield of 95.7% can be obtained over Ni/BHA-HSA (40 wt% of NiO loading) at 400 °C and 3.0 MPa, and a lifetime test shows that, at 500 °C and 3.0 MPa, it is more stable than Ni/BHA. The serious aggregation of Ni nanoparticles is the major reason for the deactivation of the latter. The work demonstrates that BHA-HSA can be effectively prepared using carbon black as the hard template and is more suitable as a Ni catalyst support for CO methanation.

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 H2/CO (and H2/CO2), and the addition of other compounds (H2O, O2, 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 H2/CO (and H2/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 O2 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.

CO methanation reaction over the Ni/Al2O3 catalysts for synthetic natural gas production was systematically investigated by tuning a number of parameters, including using different commercial Al2O3 supports and varying NiO and MgO loading, calcination temperature, space velocity, H2/CO ratio, reaction pressure, and time, respectively. The catalytic performance was greatly influenced by the above-mentioned parameters. Briefly, a large surface area of the Al2O3 support, a moderate interaction between Ni and the support Al2O3, a proper Ni content (20 wt %), and a relatively low calcination temperature (400 °C) promoted the formation of small NiO particles and reducible β-type NiO species, which led to high catalytic activities and strong resistance to the carbon deposition, while addition of a small amount of MgO (2 wt %) could improve the catalyst stability by reducing the carbon deposition; other optimized conditions that enhanced the catalytic performance included high reaction pressure (3.0 MPa), high H2/CO ratio (≥3:1), low space velocity, and addition of quartz sand as the diluting agent in catalyst bed. The best catalyst combination was 20–40 wt % of NiO supported on a commercial Al2O3 (S4) with addition of 2–4 wt % of MgO, calcined at 400–500 °C and run at a reaction pressure of 3.0 MPa. On this catalyst, 100% of CO conversion could be achieved within a wide range of reaction temperature (300–550 °C), and the CH4 selectivity increased with increasing temperature and reached 96.5% at a relatively low temperature of 350 °C. These results will be very helpful to develop highly efficient Ni-based catalysts for the methanation reaction, to optimize the reaction process, and to better understand the above reaction.

We report the preparation and characterization of Ni nanoparticles supported on barium hexaaluminate (BHA) as CO methanation catalysts for the production of synthetic natural gas (SNG). BHA with a high thermal stability was synthesized by a coprecipitation method using aluminum nitrate, barium nitrate, and ammonium carbonate as the precursors. The Ni catalysts supported on the BHA support (Ni/BHA) were prepared by an impregnation method. X-ray diffraction, nitrogen adsorption, transmission electron microscopy, thermogravimetric analysis, H2 temperature-programmed reduction, O2 temperature-programmed oxidation, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy are used to characterize the samples. The CO methanation reaction was carried out at pressures of 0.1 and 3.0 MPa, weight hourly space velocities (WHSVs) of 30 000, 120 000, and 240 000 mL·g–1·h–1, with a H2/CO feed ratio of 3, and in the temperature range 300–600 °C. The results show that although the BHA support has a relatively low surface area, Ni/BHA catalysts displayed much higher activity than Al2O3-supported Ni catalysts (Ni/Al2O3) with a similar level of NiO loading even after high temperature hydrothermal treatment. Nearly 100% CO conversion and 90% CH4 yield were achieved over Ni/BHA (NiO, 10 wt %) at 400 °C, 3.0 MPa, and a WHSV of 30 000 mL·g–1·h–1. Long time testing indicates that, compared to Ni/Al2O3 catalyst, Ni/BHA is more stable and is highly resistant to carbon deposition. The superior catalytic performance of the Ni/BHA catalyst is probably related to the relatively larger Ni particle size (20–40 nm), the high thermal stability of BHA support with nonacidic nature, and moderate Ni–BHA interaction. The work demonstrates BHA would be a promising alternative support for the efficient Ni catalysts to SNG production.

The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g−1·h−1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 °C (Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.The correlation between the phase structures and surface acidity of the Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in CO methanation is systematically investigated.Download full-size image

Nickel catalysts supported on the perovskite oxide CaTiO3 (CTO) were prepared by an impregnation method for CO methanation to produce synthetic natural gas (SNG). X-Ray diffraction, nitrogen adsorption, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, H2-temperature programmed reduction and desorption, and X-Ray photoelectron spectroscopy were employed for the characterization of samples. The results revealed that the Ni/CTO catalysts showed a better performance than Ni/Al2O3 for CO methanation at various reaction conditions. The life time test at 600 °C and 3.0 MPa indicates that Ni/CTO is also more active, thermally stable and resistant to carbon deposition. This is because of the relatively weak Ni–CTO support interaction, highly stable CTO support, the absence of acidic sites on the surface of CTO and the proper Ni particle size of about 20–30 nm. The work is important for the development of effective methanation catalysts for SNG production.

A series of α-Al2O3-supported Ni catalysts with different Ni particle sizes (5–10, 10–20, and 20–35 nm) were prepared and applied in the CO methanation reaction for the production of synthetic natural gas (SNG). The catalytic tests showed that the Ni nanoparticles influenced the catalytic performance in the CO methanation, and the catalyst with a Ni nanoparticle size of 10–20 nm showed the highest CO conversion, CH4 yield, and turnover frequency, and the lowest carbon deposition, demonstrating the possibility of improving the Ni/α-Al2O3 catalysts in the CO methanation for SNG production by controlling their Ni particle size.