Preferential CO oxidation on Ru/Al2O3 catalyst: An investigation by considering the simultaneously involved methanation

The CO removal with preferential CO oxidation (PROX) over an industrial 0.5% Ru/Al₂O₃ catalyst from simulated reformates was examined and evaluated through considering its simultaneously involved oxidation and methanation reactions. It was found that the CO removal was fully due to the preferential oxidation of CO until 383 K. Over this temperature, the simultaneous CO methanation was started to make a contribution, which compensated for the decrease in the removal due to the decreased selectivity of PROX at higher temperatures. This consequently kept the effluent CO content as well as the overall selectivity estimated as the ratio of the removed CO amount over the sum of the consumed O₂ and formed CH₄ amounts from apparently increasing with raising reaction temperature from 383 to 443 K when the CO₂ methanation was yet not fully started. At these temperatures the tested catalyst enabled the initial CO content of up to 1.0 vol.% to be removed to several tens of ppm at an overall selectivity of about 0.4 from simulated reformates containing 70 vol.% H₂, 30 vol.% CO₂ and with steam of up to 0.45 (volume) of dry gas. Varying space velocity in less than 9000 h⁻¹ did not much change the stated overall selectivity. From the viewpoint of CO removal the article thus concluded that the methanation activity of the tested Ru/Al₂O₃ greatly extended its working temperatures for PROX, demonstrating actually a feasible way to formulate PROX catalysts that enable broad windows of suitable working temperatures.     

Promotion of CO2 methanation activity and CH4 selectivity at low temperatures over Ru/CeO2/Al2O3 catalysts

The effect of CeO₂ loading amount of Ru/CeO₂/Al₂O₃ on CO₂ methanation activity and CH₄ selectivity was studied. The CO₂ reaction rate was increased by adding CeO₂ to Ru/Al₂O₃, and the order of CO₂ reaction rate at 250 °C is Ru/30%CeO₂/Al₂O₃ > Ru/60%CeO₂/Al₂O₃ > Ru/CeO₂ > Ru/Al₂O₃. With a decrease in CeO₂ loading of Ru/CeO₂/Al₂O₃ from 98% to 30%, partial reduction of CeO₂ surface was promoted and the specific surface area was enlarged. Furthermore, it was observed using FTIR technique that intermediates of CO₂ methanation, such as formate and carbonate species, reacted with H₂ faster over Ru/30%CeO₂/Al₂O₃ and Ru/CeO₂ than over Ru/Al₂O₃. These could result in the high CO₂ reaction rate over CeO₂-containing catalysts. As for the selectivity to CH₄, Ru/30%CeO₂/Al₂O₃ exhibited high CH₄ selectivity compared with Ru/CeO₂, due to prompt CO conversion into CH₄ over Ru/30%CeO₂/Al₂O₃.     

Methane thermocatalytic decomposition to COx-free hydrogen and carbon nanomaterials over Ni–Mn–Ru/Al2O3 catalysts

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO_x-free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al₂O₃ catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N₂ adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al₂O₃ catalyst using Ru(NO)(NO₃)_x(OH)_y(x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/g_cat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al₂O₃ catalysts.     

Modeling study on a two-stage hydrogen purification process of pressure swing adsorption and carbon monoxide selective methanation for proton exchange membrane fuel cells

A two-stage hydrogen purification process based on pressure swing adsorption (PSA) and CO selective methanation (CO-SMET) is proposed to meet the stringent requirements of H₂-rich fuel for kW-scale skid-mounted or distributed proton exchange membrane fuel cell systems. The reforming gas is purified using dynamic adsorption model of PSA with activated carbon for initial purification and then kinetic model of CO-SMET with 50 wt% Ni/Al₂O₃ for CO deep removal. Sensitive analyses of the gas hourly space velocity, adsorption time and adsorption pressure etc. are studied. The results show that excellent H₂ purity and CO concentration below 1000 ppm for the initial target using the three-bed and four-bed PSA system at shorter adsorption time and higher pressure, and then CO concentration below 10 ppm with H₂ purity over 99.94% on CO-SMET. This work provides a small-scale and hydrogen-saving process for hydrogen purification can be achieved by the two-stage process.     

Comparison of structure and catalytic performance of Pt–Co and Pt–Cu bimetallic catalysts supported on Al2O3 and CeO2 synthesized by electron beam irradiation method for preferential CO oxidation

In order to investigate the effect of transition metal addition to platinum with different support materials on preferential CO oxidation, structure and chemical properties of supported bimetallic catalysts prepared by electron beam irradiation method were correlated to the catalytic performance. On Al₂O₃, decoration of Pt by small amount of Co (Co/Pt ∼ 0.03) drastically increased CO and O₂ conversions while addition of equimolar Cu to Pt increased them only above 100 °C, where the rate-controlling factor was suggested to change from oxygen transport to CO activation. On CeO₂, either addition of Co or Cu to Pt had minor or negative effect on high O₂ conversion inherent to high oxygen transport at Pt–CeO₂ interface. On Pt–Cu/CeO₂, however, metal-CuO_x interface dominates the reaction characteristics to give improved selectivity, which is suitable for deep CO removal in excess O₂/CO condition. The order of selectivity above 100 °C, Pt–CoO_x > Pt(alloy)–CuO_x > Pt–CeO₂ interfaces, was derived from structural analysis and catalytic tests.     

The influence of CO,CO2 and H2O on selective CO methanation over Ni(Cl)/CeO2 catalyst: On the way to formic acid derived CO-free hydrogen

For the first time the influence of CO, CO₂ and H₂O content on the performance of chlorinated NiCeO₂ catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO₂ increases with the increasing H₂ concentration, is independent of CO₂ concentration and decreases with increasing CO and H₂O concentrations; the rate of CO₂ methanation is weakly sensitive to H₂ and CO₂ concentrations and decreases with increasing CO and H₂O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO₂ hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO₂ was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO₂ (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO₂-η-Al₂O₃/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.     

Removing CO and acetaldehyde from hydrogen streams generated by ethanol reforming

It is well known that CO depletion from the hydrogen is compulsory in order to avoid the poisoning of the anode electrocatalyst of the PEM fuel cell. Hydrogen generated by ethanol reforming contains CO and acetaldehyde. The latter can be decomposed on the electrocatalyst generating more CO. The decarbonylation and methanation reactions are proposed by this work in order to eliminate acetaldehyde and CO from the hydrogen stream. Our results show that Ru/Al₂O₃ is more active than Ni/SiO₂ for the methanation reaction. These catalysts also promote the decarbonylation of acetaldehyde generating methane and CO, with Ni/SiO₂ being much more active than the Ru catalyst. The performance of a double-bed reactor in the purification of hydrogen generated by ethanol reforming is described in this contribution. The first layer composed of Ni/SiO₂ decomposes acetaldehyde producing methane and CO, which is then eliminated by the methanation reaction employing Ru/Al₂O₃ in the second layer.     

Design and test of a miniature hydrogen production reactor integrated with heat supply,fuel vaporization,methanol-steam reforming and carbon monoxide removal unit

This study presents a designed and tested integrated miniature tubular quartz-made reactor for hydrogen (H₂) production. This reactor is composed of two concentric tubes with an overall length of 60 mm and a diameter of 17 mm. The inner tube was designed as the combustor using Pt/Al₂O₃ as the catalyst. The gap between the inner and outer tubes is divided into three sections: a liquid methanol-water vaporizer, a methanol-steam reformer using RP-60 as the catalyst and a carbon monoxide (CO) methanator using Ru/Al₂O₃ as the catalyst. The experimental measurements indicated that this integrated reactor works properly as designed. The methanol conversion, hydrogen production rate and CO concentration were found to increase with an increasing methanol/air flow rate in the combustor and decreases with an increasing methanol/water feed rate to the reformer. The methanator experimental results indicated that the CO conversion and H₂ consumption can be enhanced by increasing the Ru loading. It was also found that the CO methanation depends greatly on the reaction temperature. With a higher reaction temperature, the CO methanation, carbon dioxide (CO₂) methanation, and reversed water gas shift reactions took place simultaneously. CO conversion was found to decrease while H₂ consumption was found to increase. At a lower reaction temperature both the CO conversion and H₂ consumption were found to increase indicating that only CO methanation took place. From the experimental results the maximum methanol conversion, hydrogen yield, and CO conversion achieved were 97%, 2.38, and 70%, respectively. The actual lowest CO concentration and maximum power density based on the reactor volume were 90 ppm and 0.8 kW/L, respectively.     

The effects of bimetallic Co–Ru nanoparticles on Co/RuO2/Al2O3 catalysts for the water gas shift and methanation

The effects of Co on RuO₂/Al₂O₃'s activities for water gas shift (WGS) and methanation were studied. Catalysts were characterized with BET, XRD, SEM/EDS, H₂-TPR and CO-TPR. The effects of various parameters, such as calcination temperature, Ru–Co loading, Ru/Co ratio, inlet CO concentration and H₂O/CO ratio on the activities of catalysts were investigated. There existed Co_I (strongly interact with RuO₂) and Co_II (weakly interact with RuO₂). For Co/RuO₂/Al₂O₃ (Ru/Co = 1, AT = 350), only Co_I existed as bimetallic Co–Ru nanoparticles. This unique structure led this catalyst to achieve the highest CO conversion of 98.6% exceeding WGS's theoretical thermodynamic equilibrium limit due to the co-occurrence of methanation. Co/RuO₂/Al₂O₃ was more favorable to catalyze CO methanation than CO₂ methanation. The apparent activation energies of forward and reverse WGS catalyzed by Co/RuO₂/Al₂O₃ were 37.8 and 74.6 kJ mol⁻¹, respectively. The difference was corresponding well to the enthalpy change (−41.1 kJ mol⁻¹) of WGS.     

Catalytic steam reforming of complex gasified biomass tar model toward hydrogen over dolomite promoted nickel catalysts

The complex mixture of gasified tar model (phenol, toluene, naphthalene, and pyrene) was steam reformed for hydrogen production over 10 wt% nickel based catalysts. The catalysts were prepared by co-impregnation method with dolomite promoter and various oxide supports (Al₂O₃, La₂O₃, CeO₂, and ZrO₂). Steam reforming was carried out at 700 °C at atmospheric pressure with steam to carbon molar ratio of 1 and gas hourly space velocity of 20 L/h·g_cat. The catalysts were characterised for reducibility, basicity, crystalline, and total surface area properties. Dolomite promoter strengthened the metal-support interaction and basicity of catalyst. The Ni/dolomite/La₂O₃ (NiDLa) catalyst with mesoporous structure (26.42mn), high reducibility (104.42%), and strong basicity (5.56 mmol/g) showed superior catalytic performance in terms of carbon conversion to gas (77.7%), H₂ yield (66.2%) and H₂/CO molar ratio (1.6). In addition, the lowest amount of filamentous coke was deposited on the spent NiDLa after 5 h.     

Study on water–gas shift reaction performance using Pt-based catalysts at high temperatures

The water–gas shift reaction (WGSR) performance was experimentally studied using Pt-based catalysts for temperature, time factor and steam to carbon (S/C) molar ratio at ranges of 750–850 °C, 10–20 g_cat h/mol_CO, and 1–5, respectively. Al₂O₃ spheres were used as the catalyst support. For the high S/C cases, it was found that CO conversion can be enhanced when Pt/CeO₂/Al₂O₃ catalyst was used as compared with Pt/Al₂O₃. For the low S/C ratio cases, CO conversion enhancement was not significant with the addition of CeO₂. It was also found that CO conversion was not influenced by the CeO₂ amount to a large extent. Using bimetallic Pt–Ni/CeO₂/Al₂O₃ catalyst, it was found that higher CO conversion can be obtained as compared with CO conversions obtained from monometallic catalysts (Pt/Al₂O₃ or Pt/CeO₂/Al₂O₃). The experimental data also indicated that good thermal stability can be obtained for the Pt-based catalysts studied.     

Development of highly effective supported nickel catalysts for pre-reforming of liquefied petroleum gas under low steam to carbon molar ratios

The pre-reforming of commercial liquefied petroleum gas (LPG) was investigated over Ni–CeO₂ catalysts at low steam to carbon (S/C) molar ratios less than 1.0. It was found that the catalytic activity and selectivity depended strongly on the nature of the support and the interaction between Ni and CeO₂. The Ni–CeO₂/Al₂O₃ catalysts, which were prepared by impregnating boehmite (AlOOH) with an aqueous solution of cerium and nickel nitrates, exhibited the optimal catalytic activity and remarkable stability for the steam reforming of LPG in the temperature range of 275–375 °C. The effects of CeO₂ loading, reaction temperature and S/C ratio on the catalytic behavior of the Ni–CeO₂/Al₂O₃ catalysts were discussed in detail. The results showed that the catalysts with 10 wt.% CeO₂ had the highest catalytic activity, and higher S/C ratios contributed to LPG reforming and the methanation of carbon oxides and hydrogen. The XRD and H₂-TPR analyses revealed that the strong interaction between Ni and CeO₂ resulted in the formation of CeAlO₃ in the Ni–CeO₂/Al₂O₃ catalysts reduced. The stability tests of 15Ni–10CeO₂/Al₂O₃ catalyst at 350 °C indicated that the catalyst was stable, and the stability could be enhanced by increasing S/C ratio.     

Oxygen removal from syngas by catalytic oxidation of copper catalyst

The syngas from biomass gasification may contain trace oxygen besides of gaseous hydrocarbons, which will result in the temporarily or even permanently deactivation of Fischer–Tropsch (F–T) catalysts. In this paper, CuO–CeO₂/Al₂O₃ catalyst was developed to efficiently remove the trace oxygen from biomass syngas. The experimental results demonstrated that CuO–CeO₂/Al₂O₃ catalyst was considerably effective in removing oxygen to the level of below 1 ppm, its lifetime and deoxygenation capacity were 160 h and 3000 ml/g, respectively. Moreover, the optimum conditions of CuO–CeO₂/Al₂O₃ catalyst were 200 °C, 3.45 × 10⁵ Pa, and 3000 h⁻¹ gas hourly space velocity.     

Effects of synthesis route on the performance of mesoporous ceria-alumina and ceria-zirconia-alumina supported nickel catalysts in steam and autothermal reforming of diesel

Decline in catalyst performance due to coke deposition is the main problem in diesel steam (SR) and autothermal reforming (ATR) reactions. Good redox potential and strong interaction of CeO₂ with nickel increase activity and coke resistivity of Ni/Al₂O₃ catalysts. In this study, mesoporous Al₂O₃, CeO₂/Al₂O₃, and CeO₂/ZrO₂/Al₂O₃ supported nickel catalysts were successfully synthesized. The highest hydrogen yield, 97.7%, and almost no coke deposition were observed with CeO₂/ZrO₂/Al₂O₃ catalyst (Ni@8CeO₂-2ZrO₂-Al₂O₃-EISA) in SR reaction. The second highest hydrogen yield, 91.4%, was obtained with CeO₂/Al₂O₃ catalyst (Ni@10CeO₂-Al₂O₃-EISA) with 0.3 wt% coke deposition. Presence of ZrO₂ prevented the transformation of cubic CeO₂ into CeAlO₃, which enhanced water gas shift reaction (WGSR) activity. Ni@10CeO₂-Al₂O₃-EISA did not show any decline in activity in a long-term performance test. Higher CeO₂ incorporation (20 wt%) caused lower steam reforming activity. Change of synthesis route from one-pot to impregnation for the CeO₂ incorporation decreased the number of acid sites, limiting cracking reactions and causing a significant drop in hydrogen production.     

The cleanup of CO in hydrogen for PEMFC applications using Pt,Ru, Co,and Fe in PROX reaction

An experimental investigation is performed into the cleanup of CO in hydrogen for proton exchange membrane fuel cell (PEMFC) using Pt/Al₂O₃ and Ru/Al₂O₃ catalysts. Additionally, the effects of adding the transition metals Co and Fe to a Ru/Al₂O₃ catalyst are examined. The results show that as the level of Pt addition is increased, the maximum CO conversion rate is achieved at a lower temperature. With Ru/Al₂O₃ catalysts, the CO conversion rate increases significantly with increasing Ru addition at temperatures lower than 80 °C For both catalysts, the methane yield increases with increasing temperature and increasing noble metal addition. At temperatures in the range of 100–140 °C, the CO conversion rate and methane yield of the Pt- and Ru-based preferential oxidation (PROX) reactions are both insensitive to the density of the honeycomb carrier. The CO conversion rate is significantly improved by the addition of Fe at temperatures lower than 160 °C and by the addition of Co at temperatures higher than 200 °C. Of the two metals, Fe results in a greater reduction of the methane yield at high temperatures. Finally, both catalysts achieve a stable cleanup performance over the course of a 12-h stability test and suppress the CO concentration to an acceptable level for PEMFC applications.     

Biohydrogen synthesis from catalytic steam gasification of furniture waste using nickel catalysts supported on modified CeO2

Present study evaluated the catalytic steam gasification of furniture waste to enhance the biohydrogen production. To do this, 10 wt% nickel loaded catalysts on the variety of supports (Al₂O₃, CeO₂, CeO₂-La₂O₃, and CeO₂–ZrO₂) were prepared by the novel solvent deficient method. The hydrogen selectivity (vol%) order of the catalysts was achieved as Ni/CeO₂–ZrO₂>Ni/CeO₂>Ni/Al₂O₃?Ni/CeO₂-La₂O₃. The best catalytic activity of Ni/CeO₂–ZrO₂ catalyst (~82 vol % H₂ at 800 °C) was ascribed to the smaller size of nickel crystals, finely dispersed Ni on the catalyst surface, and Ce_1-xZr_xO_2-δ solid solution. The role of Ce_1-xZr_xO_2-δ solid solution in Ni/CeO₂–ZrO₂ catalyst was observed as bi-functional; acceleration of water-gas-shift and oxidation of carbon reaction. The high resistance of Ni/CeO₂–ZrO₂ towards the coke formation showed its potential to establish a cost-effective commercial-scale biomass steam gasification process. This study is expected to provide a promising solution for the disposal of furniture wastes for production of clean energy (biohydrogen).     

Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al₂O₃ catalysts with various Co loadings, and the prepared catalysts were used in CO₂ methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al₂O₃ sample with a specific surface area of 129.96 m²/g possessed the highest catalytic performance in CO₂ methanation (76.2% CO₂ conversion and 96.39% CH₄ selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.     

Cyclic molecular designed dispersion (CMDD) of Fe2O3 on CeO2 promoted by Au for preferential CO oxidation in hydrogen

A novel cyclic molecular designed dispersion (CMDD) method was employed to uniformly deposit 0.0–6.5 wt% Fe on CeO₂. The gold catalysts (0.0–3.8 wt%) supported on Fe₂O₃-CeO₂ were tested for CO preferential oxidation (PROX). As the CMDD method involved grafting of Fe (acac)₃ onto the surface –OH groups, 2.7 surface –OH/nm² was determined for the CeO₂ by using the Grignard reagent. The performance of CMDD catalysts was compared with the corresponding catalysts prepared by impregnation. The catalysts were characterized by XPS, XRD, TPR, HRTEM-EDX, BET and ICP. The results suggested that Au/Fe₂O₃-CeO₂ was significantly more active and selective than Au/CeO₂. The CMDD-prepared catalysts with 1.4–2.5 wt% iron showed the highest activity and selectivity, especially at temperatures as low as 323 K. The formation of Ce-Fe solid solution for CMDD catalysts promoted the dispersion of both iron and gold. Highly dispersed gold nanoparticles mainly as small as 2.2 nm were observed in HRTEM.     

Effect of support composition and metal loading on Au catalyst activity in steam reforming of methanol

Gold (Au) supported on CeO₂–Fe₂O₃ catalysts prepared by the deposition-coprecipitation technique were investigated for steam reforming of methanol (SRM). The 3 wt% Au/CeO₂–Fe₂O₃ sample calcined at 400 °C achieved 100% methanol conversion and 74% hydrogen yield due to a strong Ce–Fe interaction in the active solid solution phase, Ce_xFe_1−xO₂. The sintering of Au particles was observed when the highest metal content of 5 wt% was registered, which worsened the SRM activity. According to the TPR and TPO analysis, it was found that the transformation of the α-Fe₂O₃ structure in the mixed oxides and the coke deposition were the main factors for the rapid deactivation of the catalyst.     

Preferential oxidation of CO in H2 stream on Au/CeO2–TiO2 catalysts

A series of Au catalysts supported on CeO₂–TiO₂ with various CeO₂ contents were prepared. CeO₂–TiO₂ was prepared by incipient-wetness impregnation with aqueous solution of Ce(NO₃)₃ on TiO₂. Gold catalysts were prepared by deposition–precipitation method at pH 7 and 65 °C. The catalysts were characterized by XRD, TEM and XPS. The preferential oxidation of CO in hydrogen stream was carried out in a fixed bed reactor. The catalyst mainly had metallic gold species and small amount of oxidic Au species. The average gold particle size was 2.5 nm. Adding suitable amount of CeO₂ on Au/TiO₂ catalyst could enhance CO oxidation and suppress H₂ oxidation at high reaction temperature (>50 °C). Additives such as La₂O₃, Co₃O₄ and CuO were added to Au/CeO₂–TiO₂ catalyst and tested for the preferential oxidation of CO in hydrogen stream. The addition of CuO on Au/CeO₂–TiO₂ catalyst increased the CO conversion and CO selectivity effectively. Au/CuO–CeO₂–TiO₂ with molar ratio of Cu:Ce:Ti = 0.5:1:9 demonstrated very high CO conversion when the temperature was higher than 65 °C and the CO selectivity also improved substantially. Thus the additive CuO along with the promoter and amorphous oxide ceria and titania not only enhances the electronic interaction, but also stabilizes the nanosize gold particles and thereby enhancing the catalytic activity for PROX reaction to a greater extent.