High Methanation Activity Research Articles

Nickel-promoted mesoporous ZSM5 for carbon monoxide methanation

Synergistic effect of Ni and the mZSM5 support led to high methanation activity of Ni/mZSM5. Two possible reaction routes emerged: (1) adsorbed CO may be reacted with H2 to form CH4 and H2O; (2) adsorbed H may be reacted with CO to form CH4 and CO2.

High CO methanation activity on zirconia-supported molybdenum sulfide catalyst

In this study, different methods were used to prepare MoO3/ZrO2 catalysts for sulfur resistant methanation reaction. It was found that MoO3/ZrO2 catalyst prepared by one-step co-precipitation method achieved high methanation performance. CO conversion could reach up to 90% on 25 wt% MoO3/ZrO2 catalyst, much higher than that on the conventional 25 wt% MoO3/Al2O3 catalyst. The Mo-based catalysts were characterized by XRF, XRD, Raman, BET, TEM and H2-TPR etc. It was found that MoO3 particles were highly dispersed on ZrO2 support for 25 wt% MoO3/ZrO2 catalyst prepared at 65–85 °C because of its relatively larger pore size, which contributed to a high CO conversion. Meanwhile, when MoO3 loading exceeded the monolayer coverage, the formed crystalline MoO3 and ZrMo2O8 might block the micropores of the catalyst and make the methanation activity declined. These results are useful for preparing highly efficient catalyst for CO methanation process.

Preparation of Ru nanoparticles on TiO2using selective deposition method and their application to selective CO methanation

Selective CO methanation was investigated over Ru/TiO2 prepared using a selective deposition method with NaOH and NH3 aqueous solution as a pH adjuster. Control of pH by NH3 solution resulted in the small particle size of Ru (average 1.2 nm) and the formation of Na-free Ru/TiO2, leading to high CO methanation activity and a wide temperature window for selective CO methanation at low temperatures.

Effect of metal addition to Ru/TiO2 catalyst on selective CO methanation

Selective CO methanation over Ru/TiO2, Ru-Ni/TiO2, Ru-Co/TiO2, Ru-Fe/TiO2, Ru-La/TiO2, Ru-K/TiO2, and Ru-Ni-La/TiO2 was investigated as a CO removal method from reformate gas for polymer electrolyte fuel cell applications, and the selectivity and activity were examined. The addition of Co and La to Ru/TiO2 improved both CO and CO2 methanation, while the addition of Ni raised only the activity for CO methanation. The addition of La increased the electron density in the Ru species, which likely enhanced the dissociation of the CO bond of CO on Ru probably due to back donation of electrons from Ru to CO. This led to high CO methanation activity over Ru-La/TiO2. The trimetallic catalyst Ru-Ni-La/TiO2 showed the highest CO methanation activity among the prepared catalysts, resulting in a wider temperature range for selective CO methanation at low temperatures compared to Ru/TiO2.

Investigation of sulfur-resistant, highly active unsupported MoS2 catalysts for synthetic natural gas production from CO methanation

This paper reports on an enhanced activity of sulfur-resistant methanation catalyst by introducing sulfur powder instead of toxic H2S in catalyst preparation. Ammonium heptamolybdate (AHM) was a suitable precursor for this catalyst preparation based on consideration of economy and activity. The effect of S/AHM weight ratio and sulfidation atmosphere on catalyst methanation performance was studied and the optimum S/AHM ratio was 3. Sulfidation atmosphere affected not only methanation activity but also the structure and morphology of the catalysts. The catalyst treated in inert atmosphere exhibited relatively the highest methanation activity with CO conversion as high as 88.2%, which was approaching the thermodynamic equilibrium value. The catalysts characterization results indicated that the as-prepared catalyst at S/AHM ratio as 3 had relatively higher specific surface area and larger pore volume than those with other S/AHM ratio. The MoS2 particles were poorly crystallized with long and straight multi-layered slabs. For the catalyst treated in nitrogen environment, more weakly-bonded sulfur species existed on the surface and more sulfur vacancies resided on the edge planes of MoS2 particles, which are considered to be the active sites for methanation.

Ni/CeO2 catalysts with high CO2 methanation activity and high CH4 selectivity at low temperatures

CO2 methanation was performed over 10 wt%Ni/CeO2, 10 wt%Ni/α-Al2O3, 10 wt%Ni/TiO2, and 10 wt%Ni/MgO, and the effect of support materials on CO2 conversion and CH4 selectivity was examined. Catalysts were prepared by a wet impregnation method, and characterized by BET, XRD, H2-TPR and CO2-TPD. Ni/CeO2 showed high CO2 conversion especially at low temperatures compared to Ni/α-Al2O3, and the selectivity to CH4 was very close to 1. The surface coverage by CO2-derived species on CeO2 surface and the partial reduction of CeO2 surface could result in the high CO2 conversion over Ni/CeO2. In addition, superior CO methanation activity over Ni/CeO2 led to the high CH4 selectivity.

The influence of metals and acidic oxide species on the steam reforming of dimethyl ether (DME)

Abstract The performance of catalysts from the platinum group and Cu-based catalysts were compared in the dimethyl ether (DME) steam reforming reaction. Without acidic oxides, Cu-based catalysts formed undesired CH4 via a direct decomposition of DME into methoxy (–OCH3) and methyl (–CH3) groups, followed by the hydrogenation of the methyl group to CH4. However, in the presence of acidic oxides such as Al2O3, practically no CH4 was produced. Therefore we speculate that the MeOH formed on the acidic sites moves onto Cu and is adsorbed as a methoxy group without the co-formation of a methyl group, preventing the formation of CH4 and leading to an even higher yield of H2. Pt/Al2O3 and Ru/Al2O3 showed a relatively high DME conversion, although the undesired production of CH4 was quite high, irrespective of the presence of acidic sites. A high CH4 selectivity can be explained in terms of a high methanation activity. The catalyst formed from CuMn2O4 spinel oxide mixed with Al2O3 showed higher activity and greater durability than commercial CuZnAl catalysts mixed with Al2O3. By replacing Al2O3 with H-ZSM5, the CuMn2O4 spinel oxide showed a further increase in activity resulting in up to 100% conversion even under 300 °C. We attribute this very high activity at relatively low temperature to both the high DME hydration activity of H-ZSM5 and the high MeOH steam reforming activity of CuMn2O4 spinel oxide.

Influence of lanthanum on the performance of Zr-Co/activated carbon catalysts in Fischer-Tropsch synthesis

The influence of La loading on Zr-Co/activated carbon (AC) catalysts has been studied for Fischer-Tropsch synthesis. The catalyst samples were characterized by XRD, TPR, CO-TPD, and temperature programmed CO hydrogenation. The catalytic property was evaluated in a fixed bed reactor. The experimental results showed that CO conversion increased from 86.4% to 92.3% and the selectivity to methane decreased from 14.2% to 11.5% and C 5+ selectivity increased from 71.0% to 74.7% when low La loading (La = 0.2wt%) was added into the Zr-Co/AC catalyst. However, high loadings of La (La = 0.3–1.0 wt%) would decrease catalyst activity as well as the C 5+ selectivity and increase methane selectivity. XRD results displayed that La-modified Zr-Co/AC catalyst had little effect on the dispersion of Co catalyst. But, the results of TPR, CO-TPD, and temperature programmed CO hydrogenation techniques indicated that the extent of cobalt reduction was found to greatly influence the activity and selectivity of the catalyst. The addition of a small amount of La increased the reducibility of the Zr-Co/AC catalyst and restrained the formation of methane and improved the selectivity to long chain hydrocarbons. However, excess of La led to the decrease of the reducibility of Co catalyst thus resulted in higher methanation activity.

Methanation on K+-modified Pt/SiO2: the impact of reaction conditions on the effective role of the promotor

This paper reports on the first study that the authors know of of the effect of alkali promotion of Pt on methanation. Methanation was investigated on a 4.5 wt% Pt/SiO2 catalyst promoted with different amounts of K+ (K+/Pt=0, 0.1, and 0.2) for two different temperature ranges (503-552 K and 573-665 K). The methanation rate was 10-70% lower on the promoted catalysts for reaction temperatures of 573 to 665 K. In this temperature range, the relative decrease in rate upon promotion was a function of K+ loading and did not vary with temperature, \(p_{H_2 } ,p_{{\text{CO}}} \), or time-on-stream. In addition, there was no significant effect of K+-promotion on activation energy (ca. 29 kcal/mol) or methanation reaction orders with respect to CO and H2 (-0.1-0.0 and 0.4-0.6, respectively). However, there was a decrease in the number of methane-destined surface intermediates upon promotion as determined by steady-state isotopic transient kinetic analysis (SSITKA). All these observations lead to the conclusion that, in this higher reaction temperature range, K+ acts mainly as a site-blocking agent for methanation on Pt and does not change the reaction rate of the limiting step, probably hydrogenation. Between 503 and 552 K, the activation energy and reaction orders with respect to H2 and CO were also not affected by K+. However, the catalyst with a K+/Pt ratio of 0.1 showed the highest methanation activity. In this lower temperature range and for all the catalysts, the apparent activation energies were also found to be lower, 18 vs. 29 kcal/mol, compared to those at higher temperatures. The reaction order with respect to CO was higher (0.2-0.3) in comparison with what was observed in the higher temperature range (ca. -0.1-0.0). These results suggest, that, in the low temperature range and for low loadings of K+, K+ affects the rate-determining step resulting in a rate increase greater than the decrease due to the blockage effect. Thus, K+ serves as a rate promoter at low reaction temperatures while its only effective function is site blockage at higher temperatures.

Temperature-programmed methanation on Pd/La 2O 3 and Pd/SiO 2 catalysts

Temperature-programmed reaction and desorption (TPR, TPD) spectra are compared for Pd/La 2O 3 and Pd/SiO 2 catalysts for CO methanation and CO and H 2 coadsorption. A methoxy (CH 3O) species readily forms on the La 2O 3 surface of Pd/La 2O 3 by spillover, and this CH 3O hydrogenates to CH 4 at a higher rate than CO adsorbed on Pd. Carbon also deposits on the catalyst surface during TPR, and then hydrogenates at a slower rate than CH 3O. In contrast, CH 3O does not form on Pd/SiO 2 from CO and H 2, and correspondingly Pd/SiO 2 has a lower methanation activity than Pd/La 2O 3. Isotope labeling, interrupted reaction, activated adsorption, high-temperature TPD/TPR, and CH 3OH adsorption are used to study the surface processes on Pd/La 2O 3. The high methanation activity of Pd/La 2O 3 catalysts during steady-state methanation may be related to the formation and hydrogenation of CH 3O.

Semiconductivity study of ceria-supported nickel related to its methanation catalytic activity

The electrical conductivity study of a ceria-supported nickel catalyst (d≈2.1 nm) showed the presence of anionic vacancies created in ceria by reduction in hydrogen. At reaction temperature, this gas is able to spill over the surface of the oxide. It was also inferred that electrons can migrate from the support to the metal. The catalytic behaviour of Ni/CeO 2 was compared with that of a Ni/SiO 2 homologue. Ni/CeO 2 has a higher methanation activity but the selectivity with respect to methane depends strongly on the reaction temperature and the hydrogen pressure. At low temperature (533 K) and under low P H 2 , a substantial production of carbon dioxide is observed. If the temperature is increased to 573 K and if hydrogen is in large excess (H 2/CO=17), Ni/CeO 2 becomes highly active and selective with respect to methane with good stability of its activity. From the results of electrical conductivity and the variations in the selectivity, it was inferred that the active sites are formed by a surface nickel atom at the metal—support interface in close vicinity to an anionic vacancy on the support. Carbon monoxide chemisorbs on the nickel atom, where it dissociates, the oxygen atom being trapped by the anionic vacancy. For a low H 2/CO ratio, this oxygen atom is removed from the surface by reaction with a carbon monoxide molecule, thus explaining the high amount of carbon dioxide produced. For a high H 2/CO ratio, anionic vacancies are preferentially regenerated by hydrogen, which forms water and prevents the formation of carbon dioxide at the metal—support interface.

Another strong metal–support interaction: high intrinsic methanation activity of an alumina-supported platinum catalyst after high temperature reduction without loss of chemisorption ability

It has been found from pulse surface reaction rate analysis measurements that the intrinsic methanation activity of an alumina-supported platinum catalyst was increased by high temperature reduction without a marked reduction in its chemisorption ability.

Absence of high methanation activity of titania-supported rhodium, ruthenium and iridium catalysts in their strong metal–support interaction state

From pulse surface reaction rate analysis measurements, it was found that the high intrinsic methanation activity of titania-supported rhodium, ruthenium, and iridium catalysts was absent in their strong metal–support interaction state.

The effect of niobia on the methanation activity of a Pt foil

Recent work examining the interaction between titania and transition metals has indicated that a partially reduced titania overlayer can form on the surface of a titania-supported catalyst. In addition, the authors have shown that a Pt foil with a titania overlayer exhibits the same methanation rates as are reported for actual titania-supported Pt catalysts, even though complete suppression of CO and H/sub 2/ adsorption is observed. Unusual support effects are observed for metals on niobia as well. As with titania-supported catalysts, catalysts supported on niobia can exhibit suppressed adsorption of CO and H/sub 2/ while maintaining a high methanation activity. To determine whether an overlayer of niobia was responsible for the properties observed with niobia-supported catalysts, the authors have examined the methanation activity for a Pt foil with a niobia overlayer. The experimental apparatus consists of a sample attached to a magnetically manipulated, linear-motion feedthrough which can be isolated from an ultrahigh vacuum system. This system allows them to measure reaction rates at atmospheric pressures on a sample which can be characterized by Auger electron spectroscopy (AES) both before and after reaction. This system is described in more detail elsewhere. 22 references.

Studies of carbon- and hydrogen-containing adspecies present during CO hydrogenation over unsupported Ru, Ni and Rh

Isotopic tracer studies have been conducted to determine the coverages of adsorbed CO, carbon, and hydrogen on the surfaces of unsupported Ru, Rh, and Ni powders during CO hydrogenation. Two forms of hydrogen are observed on each catalyst at 298 K: a low-energy form which is in equilibrium with the gas phase and is rapidly displaced from the surface by CO adsorption and a high-energy form which is not in equilibrium with the gas phase and is not displaced by CO adsorption. The low-energy form is ascribed to hydrogen adsorbed on the exterior surfaces of the metal powder. It is proposed that the high-energy form may be hydrogen which has migrated along crystal grain boundaries into the interior of the metal powder. Adsorbed carbon and CO are also observed on each catalyst. It is demonstrated that high methanation activity correlates with the surface coverage of active carbon but not with the coverage of adsorbed hydrogen.

Mössbauer spectroscopy and methanation kinetics studies of nickel-iron alloy particles supported on titania and alumina

Nickel-iron alloy particles (Ni:Fe = 10:1) were supported on titania and alumina and studied under methanation reaction conditions: temperatures from 500 to 565 K, H 2:CO ratios from 3 to 15, and pressures near atmospheric. In situ Mössbauer spectroscopy was used to monitor the state of iron in these catalysts after reduction in H 2 at 713 and 773 K. For both supports, a significant fraction of the iron was alloyed with nickel after treatment in H 2, while the remainder was associated with the support as Fe 2+. The extent of alloy formation was greater for the titania-supported samples, indicating that iron is more reducible on titania than on alumina. Under methanation reaction conditions, some of the iron from the NiFe was oxidized to Fe 2+. For titania-supported samples, this process was partially reversible upon switching to H 2 at the same temperature, while the Fe 2+ could not be re-reduced on alumina even after treatment in H 2 at 773 K. The presence of Fe 2+ under methanation reaction conditions suggests that titanium is present as Ti 4+. Compared to NiFe on alumina, the titania-supported NiFe particles showed effects of “strong metal-support interactions” manifested by (i) higher methanation activity, (ii) higher activation energy and hydrogen partial pressure dependence of the methanation rate, (iii) slower deactivation under methanation reaction conditions, and (iv) greater selectivity toward higher hydrocarbons. These effects are explained by the presence of titania species (TiO x ) on the surface of the titania-supported NiFe particles. These species decrease the extent of carbon deposition on the metal surface, thereby increasing the amount of “active” carbon at the expense of “inactive” carbon. The probability of carbon chain-growth on the titania-supported NiFe particles can also be increased by addition of water to the H 2/CO feed.

New catalytica reports

Nickel-iron alloy particles (Ni:Fe = 10:1) were supported on titania and alumina and studied under methanation reaction conditions: temperatures from 500 to 565 K, H2:CO ratios from 3 to 15, and pressures near atmospheric. In situ Mössbauer spectroscopy was used to monitor the state of iron in these catalysts after reduction in H2 at 713 and 773 K. For both supports, a significant fraction of the iron was alloyed with nickel after treatment in H2, while the remainder was associated with the support as Fe2+. The extent of alloy formation was greater for the titania-supported samples, indicating that iron is more reducible on titania than on alumina. Under methanation reaction conditions, some of the iron from the NiFe was oxidized to Fe2+. For titania-supported samples, this process was partially reversible upon switching to H2 at the same temperature, while the Fe2+ could not be re-reduced on alumina even after treatment in H2 at 773 K. The presence of Fe2+ under methanation reaction conditions suggests that titanium is present as Ti4+. Compared to NiFe on alumina, the titania-supported NiFe particles showed effects of “strong metal-support interactions” manifested by (i) higher methanation activity, (ii) higher activation energy and hydrogen partial pressure dependence of the methanation rate, (iii) slower deactivation under methanation reaction conditions, and (iv) greater selectivity toward higher hydrocarbons. These effects are explained by the presence of titania species (TiOx) on the surface of the titania-supported NiFe particles. These species decrease the extent of carbon deposition on the metal surface, thereby increasing the amount of “active” carbon at the expense of “inactive” carbon. The probability of carbon chain-growth on the titania-supported NiFe particles can also be increased by addition of water to the H2/CO feed.