Ceria Promotion Research Articles

Cerium-promoted nickel catalysts supported on yttrium-doped γ-alumina for carbon dioxide methanation

The catalytic performance of the Ni/Al, Y-doped Ni/Al-xY, and Ce-promoted Ni-yCe/Al-15Y catalysts for CO2 methanation was examined. The CO2 conversion and CH4 yield increased in the order of Ni/Al < Ni/Al-5Y < Ni/Al-25Y < Ni/Al-15Y at temperatures below 350 °C. The reduction degree, H2 uptake, and total CO2 adsorption uptake increased in this order for the Ni/Al-xY catalysts, suggesting that doping γ-Al2O3 with a moderate amount of Y improved the interaction between the nickel and the support. When the Ni/Al-15Y catalyst was promoted by Ce with different contents (0–5 wt%), the catalyst with 2 wt% Ce exhibited the highest CO2 conversion (92.5%) and CH4 yield (92.2%) at ≤ 350 °C. As evidenced by catalyst characterization, cerium promoter results in a synergetic Ni–Ce interaction over the combined Al-15Y support, leading to the formation of finely dispersed metal species and numerous active sites for splitting of the stable C–O bond.

Effect of Cerium Promoters on an MCM-41-Supported Nickel Catalyst in Dry Reforming of Methane

Effect of Cerium Promoters on an MCM-41-Supported Nickel Catalyst in Dry Reforming of Methane

Catalysts of ceria supported on copper-chromium oxide: Ceria promotion of the CO-PROX activity

A copper-chromium mixed oxide with Cu:Cr 1:2 ratio has been prepared by a microemulsion method and employed as support of CeO2 in different amounts from 5 to 80 wt%. The catalysts have been characterized by XRD, HRTEM/XEDS, H2-TPR and XPS. The characterization results have been examined in correlation with their catalytic properties for the CO-PROX process complemented by operando-DRIFTS. The catalysts are formed by composites of CuCr2O4 and CuO on which aggregates of CeO2 nanoparticles are dispersed. Incorporation of CeO2 onto the CuCr mixed oxide appreciably enhances the CO-PROX performance of the catalyst. This is related to a promotion of the generation and stabilization of active partially reduced copper sites during the course of the interaction of the catalysts with the reactant mixture and which are evidenced to be formed on both CuCr oxide and CeO2 components of the catalysts.

Construction of Cu-Ce composite oxides by simultaneous ammonia evaporation method to enhance catalytic performance of Ce-Cu/SiO2 catalysts for dimethyl oxalate hydrogenation

The complicated ammonia evaporation method (AEM) involves many steps, such as mixing, evaporating ammonia, drying, and calcining procedures, etc. Thus it is necessary to know in which stage to introduce the promoter is the most beneficial to improve the performance of the Cu-based catalysts. By introducing a cerium promoter at different stages, a series of Ce-Cu-Si-T catalysts were designed for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The effects of the Ce3+ ions introduced at different stages on the structure and properties of the catalysts were revealed by XRD, TEM, XPS and other characterization methods. When the Ce3+ was added with Cu2+ simultaneously at the mixing stage, it was favor to form robust Cu-Ce composite oxides. The Cu-Ce composite oxides can not only provide more active sites, but also enhance the synergy between Cu0 and Cu+. Therefore, the performance of the Ce-Cu-Si-AE catalyst was significantly improved. The average conversion of DMO and the selectivity of EG were 100.0% and 95.3% for 480 h at 458 K under a high weight liquid hourly space velocity (WLHSV) of 1.2gg-catal-1h-1, respectively. However, the cerium promoter were adsorbed or aggregated on the surface of the copper species as the Ce3+ and Cu2+ were not introduced at the same stage, resulting in covering partial active sites and thus decreasing the catalytic performance for DMO hydrogenation. Therefore, this work provides considerable reference value for designing new stable nano copper-based catalysts and establishing an effective introduction mechanism for promoters.

The effects of cobalt and cerium promoters on hydrogen production performance of alumina‐supported nickel catalysts in propane steam reforming

AbstractBACKGROUND: The effects of Co and Ce promoters on the performance of Ni (10 wt%)–Co (0.0, 2.75, 5.5 wt%)/Ce (0.0, 5.0, 10.0 wt%)–Al2O3 catalysts have been studied for steam reforming of C3H8 (SRP). In this work, Ni (NO3)2 and Co (NO3)2 are co‐impregnated on the co‐precipitated Al2O3–CeO2 supports. X‐ray diffraction, N2 adsorption–desorption, H2‐temperature‐programmed reduction, high‐resolution transmission electron microscopy, scanning electron microscopy and thermogravimetric/differential thermal analysis were accomplished to explain the SRP activity of the catalysts. The performance of the resulting catalysts was evaluated under the gas hourly space velocity (GHSV) = 45 000 mL h‐1 gcat−1, T = 600 °C, steam/C3H8 ratio (S/C) = 3 and P = 1 atm.RESULTS: The experimental findings revealed that Ce and Co promoters markedly improved the catalyst activity, stability and H2 yield of Ni/Al2O3 catalyst. The sample with 2.75 wt% Co and 10.0 wt% Ce showed highest C3H8 conversion, while maximum yield of H2 was obtained for catalyst containing 5.5 wt% Co and 5.0 wt% Ce.CONCLUSION: Higher loadings of Co decreased C3H8 conversion and catalyst stability due to more coke formation on the catalyst surface, whereas Ce significantly improved catalyst resistance to coke deposition due to the enhanced Ni metal particles distribution over the support. © 2020 Society of Chemical Industry

Effect of ceria promotion on the catalytic performance of Ni/SBA-16 catalysts for CO2 methanation

The presence of Ce inside the SBA-16 structure promoted the ratio of Ce3+ and medium basic sites and thus favoured CH4 formation.

Reduced graphene oxide supported Ni-Ce catalysts for CO2 methanation: The support and ceria promotion effects

The reduced oxide graphene (RGO) supported Ni-based catalysts is prepared and modified with ceria (Ni-Ce/RGO) for CO2 methanation for the first time in the present work, and compared with the active carbon (AC) and γ-Al2O3 supported samples. The results show that the catalytic activity of the samples without ceria follow the order Ni/RGO > Ni/γ-Al2O3 > Ni/AC, vs. samples with ceria Ni-Ce/RGO > Ni-Ce/γ-Al2O3 > Ni-Ce/AC. The activities of all samples were greatly improved after ceria modification. The Ni-Ce/RGO works the best for CO2 methanation, which could reach the highest CO2 conversion of 84.5% and the highest methane yield of 83.0% at 350 °C with atmospheric pressure. The excellent catalytic performance of Ni-Ce/RGO could be attributed to the special support effect of RGO and the ceria promotion effect. The support effect of RGO could be attributed to its large surface area and surface oxygen-containing functional groups, which results in stable anchoring of the active metal. The addition of ceria promotes the Ni dispersion on the supports as well as to accelerate the positive reaction due to the oxygen vacancies of ceria.

Effects of Ce, La, Cu, and Fe promoters on Ni/MgAl2O4 catalysts in steam reforming of propane

The effects of nickel loading and type of promoter on the performance of xNi/MgAl2O4 (x=5, 10, and 15 wt%) and 10Ni-3M/MgAl2O4 (M=Ce, La, Cu, Fe) catalysts, respectively, in steam reforming of propane (SRP) were investigated. The catalyst support (MgAl2O4) was synthesized by co-precipitation method with a MgO/Al2O3 mole ratio of 1.0. The catalysts were then prepared by impregnation of nitrates of nickel and promoters on the support. The catalysts were characterized by the XRD, nitrogen adsorption-desorption, TPR, SEM, EDX mapping, and TGA, and the SRP performance was evaluated in a fixed bed reactor at reaction temperature=500–700 °C, pressure=1 atm, C3H8:N2: steam feed ratio=1:1:3, and GHSV=30,000 ml/(h·gcat) during 420 min time on stream. The results indicated that C3H8 conversion, H2 yield, and catalyst stability varied significantly with nickel loading and type of promoter in the catalyst. The 10Ni/MgAl2O4 catalyst showed highest C3H8 conversion (78%), H2 yield (49%), and stability (96%) as compared to the other unpromoted catalysts due to optimum nickel loading and less carbon deposition. Moreover, cerium promoter remarkably enhanced the performance of 10Ni-3Ce/MgAl2O4 catalyst (C3H8 conversion=93%, H2 yield=60%, and stability= 100%) via more coke gasification in the course of SRP reaction.

Steam gasification of oat hull pellets over Ni-based catalysts: Syngas yield and tar reduction

Renewable and clean energy generated from agricultural crops wastes can displace fossil fuels in heating and power generation. The abundant and low-value byproduct from agricultural industries can have a positive impact on the economy and environment of agricultural provinces in Canada and elsewhere. In this work, the effects of catalytic and non-catalytic steam gasification of oat hull pellets on syngas production and tar reduction were evaluated. For non-catalytic gasification, the impacts of temperature, between 650 and 850 °C, and steam-to-biomass ratio, between 0.25 and 0.50, were tested. Higher temperature increased fuel gas production and heating value, and decreased tar and char yields. Similar effects were observed with increasing steam-to-biomass ratio, except for char yield, which was not affected. For catalytic gasification, Ni/Al2O3 catalysts, with and without Ce, were synthesized and characterized. All catalytic gasification experiments were performed in a two-stage fixed bed reactor at 650 °C and catalyst-to-biomass ratio of 0.5. Among unpromoted catalysts, 10% Ni loading showed the lowest tar formation. Furthermore, adding cerium promoter increased metal dispersion, decreased reduction temperature, and lowered coke formation as observed in TGA. Increasing catalyst to biomass ratio from 0.2 to 1 reduced tar formation from 2.3 to 1.3% but had insignificant influence on syngas yield. As compared to non-catalytic process, using Ni-based catalysts improved the efficiency of steam gasification of oat hull pellets by increasing syngas production and decreasing tar formation. Improving the efficiency will make steam gasification a promising method to convert the agricultural wastes to a clean energy.

Influence of cerium and cesium promoters on vanadium catalyst for sulfur dioxide oxidation

We studied the catalytic performance of vanadium catalyst promoted with cerium and cesium for sulfur dioxide oxidation. The catalyst samples were characterized by FT-IR, Raman, XRD, SEM, BET and XPS. The results showed that the properties of the catalyst promoted with 4 wt% CeO2 and 7 wt% Cs2SO4 were superior to the commercial V2O5-K2SO4/SiO2 and V2O5-K2SO4-Cs2SO4/SiO2 catalysts, in terms of low temperature activity, thermal stability, SO2 oxidation efficiency and ignition temperature. The FT-IR, Raman, XRD and XPS results evidenced the formation of V2O5-Cs2S2O7 pyrosulfate, CeVO4 and CeO2 crystalline phase in V2O5-K2SO4-Cs2SO4-CeO2/SiO2 catalyst These crystalline phases play an important role in redox reaction at low temperature and can increase the available oxygen for the redox reaction. The characterization results also showed that cerium can promote the formation of pyrosulfate, increase the proportion of large macropores, and improve stability of VV at high temperature. Due to its excellent low-temperature and high-temperature activity, the V2O5-K2SO4-Cs2SO4-CeO2 /SiO2 catalyst appears to be more efficient for the conversion of SO2 in a larger concentration range.

Ceria Promoted Cu-Ni/SiO2 Catalyst for Selective Hydrodeoxygenation of Vanillin.

A ceria (CeO2) promoted Cu-Ni bimetallic catalyst supported on SiO2 (Cu-Ni/CeO2-SiO2) was prepared and evaluated for catalytic hydrodeoxygenation (HDO) of vanillin. Silica supported monometallic Cu and Ni catalysts and bimetallic Cu-Ni catalyst (Cu/SiO2, Ni/SiO2, and Cu-Ni/SiO2), without a ceria promoter, were also synthesized and tested for the same application. The highest conversion of vanillin was achieved with the Cu-Ni/CeO2-SiO2 catalyst. Vanillyl alcohol was the sole product in the initial 2 h, followed by the formation of 2-methoxy-4-methylphenol, which was observed. Characterization of the synthesized catalysts revealed the presence of overlapping crystalline phases of CuO, NiO, and CeO2 on the Cu-Ni/CeO2-SiO2 surface. We extended our study to find out the results of using CeO2 as the support of the Cu-Ni bimetallic catalyst (Cu-Ni/CeO2). Partial incorporation of Cu and Ni cations into the ceria lattice took place, leading to the decrease of specific surface area and a concomitant compromise in the conversion. In the case of the Cu-Ni/CeO2-SiO2 catalyst, the higher conversion was accredited to the facile formation of Cu+ active centers by the synergistic interaction between Ce+4/Ce+3 and Cu+2/Cu+ redox couples and the incorporation of oxygen vacancies on the catalyst surface.

CO2 Methanation in the Presence of Ce-Promoted Alumina Supported Nickel Catalysts: H2S Deactivation Studies

The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO2 methanation reaction was investigated. It was found that the activity of catalysts in CO2 methanation reaction at low reaction temperatures can be improved by the increase in nickel loading and introduction of cerium promoter. The catalysts showed high resistance for sintering and coking at high reaction temperatures. A few stages of catalysts deactivation by H2S in the methanation reaction carried out at 475 °C with the time on stream were identified. It was found that an introduction of H2S to the stream (8 ppm) did not induce rapid decrease of activity. Slight and then strong drop of CO2 conversion and simultaneously the loss of methane selectivity was observed after specific time, depending on the catalysts composition. Deactivation of catalysts was related to the nickel content and the presence of cerium. X-ray diffraction studies indicated small changes of crystallite size with the time on stream. Raman spectroscopy studies pointed out that deactivation of catalysts was not connected with formation of carbon deposits. An in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy studies showed that exposition of catalysts to the reaction mixture containing the traces of H2S led to the blocking of nickel active sites responsible for CO2 and H2 activation and successive transformation to carbonyl and formate species.

Self- regeneration of Au/CeO2 based catalysts with enhanced activity and ultra-stability for acetylene hydrochlorination

Replacement of Hg with non-toxic Au based catalysts for industrial hydrochlorination of acetylene to vinyl chloride is urgently required. However Au catalysts suffer from progressive deactivation caused by auto-reduction of Au(I) and Au(III) active sites and irreversible aggregation of Au(0) inactive sites. Here we show from synchrotron X-ray absorption, STEM imaging and DFT modelling that the availability of ceria(110) surface renders Au(0)/Au(I) as active pairs. Thus, Au(0) is directly involved in the catalysis. Owing to the strong mediating properties of Ce(IV)/Ce(III) with one electron complementary redox coupling reactions, the ceria promotion to Au catalysts gives enhanced activity and stability. Total pre-reduction of Au species to inactive Au nanoparticles of Au/CeO2&AC when placed in a C2H2/HCl stream can also rapidly rejuvenate. This is dramatically achieved by re-dispersing the Au particles to Au(0) atoms and oxidising to Au(I) entities, whereas Au/AC does not recover from the deactivation.

Ni/Ce[sbnd]Al2O3 for optimum hydrogen production from biomass/tar model compounds: Role of support type and ceria modification on desorption kinetics

This communication presents the synergistic role of ceria and alumina support type, in the gasification of glucose/toluene as biomass/tar model compounds over Ni/CeAl2O3. Two catalysts having 20 wt% nickel on a mesoporous Ce(x)-mesoAl2O3 (x = 0 or 1) were prepared via successive incipient wetness impregnation method. Two similar catalysts (i.e. Ni(20)/Ce(x)-γAl2O3, x = 0 or 1), were also prepared using a commercial γ-Al2O3 support. The catalysts show excellent activities for glucose/toluene mix feed as a biomass/tar model species. Physicochemical characterizations indicate that this method produces Ni/CeAl2O3 catalysts of moderate acidity, desirable pore size for biomass/tar conversion to syngas. Activity test in a riser simulator revealed that all the four catalysts are highly active for biomass/tar reforming at moderate temperature (i.e. 700 °C). In particular, Ni(20)/Ce-meso-Al2O3 was the best in terms of hydrogen production at low gasification temperature (i.e. 500 °C). This is due to its unique properties resulting from the synergistic effect of ceria promoter and our methodology for synthesizing Ce-doped-mesoAl2O3. For a 15 wt% mixed glucose/toluene feed at 700 °C and 30 s reaction time, the product composition over the Ni(20)/Ce-meso-Al2O3 catalyst was 74.33 mol% H2, 22.60 mol% COx and 3.06 mol% HC's (i.e. C1, C2, and C2=) with no tar in the product.

Oxy-dry reforming of propane over Ce-promoted Co\u2013Ni/Al2O3 catalyst

This paper reports the production of syngas from two types of O2-assisted dry reforming of propane, namely oxidative (O2-dosed) dry reforming (ODR) and dry (CO2-dosed) partial oxidation (DPOX). Reaction runs were conducted over alumina-supported bimetallic Co–Ni promoted with CeO2 at 120 kPa and 793–893 K. Ceria promotion improved the carbon deposition resilience of the Co–Ni catalyst. Physicochemical attributes were obtained from liquid N2 adsorption, H2 chemisorption and temperature-programmed desorption runs for NH3, CO2, CH4 and C3H8. Rate behavior under ODR, DPOX and pure dry reforming could be described consistently with empirical models that are structurally similar to Langmuir–Hinshelwood type relations. Inferences from these models allowed the postulation of the same overall reaction network for the three types of reactions albeit with variation in rate-controlling steps depending on the different product species. On the whole, DPOX seemed to be a superior option for the manufacturing of syngas for downstream olefin FT production due to reduced variability in the H2:CO ratio and the closeness to unity (0.72–0.95) of the exiting syngas over the range of O2 partial pressure used.

Nickel nanoparticles supported on silica for the partial oxidation of isooctane

A Ni-based nanoparticle catalyst was synthesized over a silica support via wet impregnation using either ethylene glycol or water. X-ray diffraction and transmission electron microscopy analysis showed that the particle size of the Ni catalyst prepared using ethylene glycol as the solvent tended to be smaller than that obtained when water was used. The resulting catalysts were tested for performance toward partial oxidation (POX) of isooctane at high weight hourly space velocities (WHSV). The results were compared with those from a Rh-based catalyst, which is commonly used for the same reaction. At a WHSV of 13.8h−1, a Ni/SiO2 catalyst with an average Ni particle size of 6.8nm exhibits higher catalytic activity and stability with an improved resistance to carbon formation than a Ni/SiO2 catalyst with an average Ni particle size of 16.6nm. The catalyst with the smaller Ni particles outperformed the supported Rh catalyst for the POX of isooctane. To further improve the Ni dispersion and enhance its ability to run at even higher WHSVs with milliseconds of residence time, ceria was used as a promoter. The ceria-promoted Ni catalyst was also prepared by the wet impregnation method using ethylene glycol as the solvent. The addition of ceria corresponded with a further reduction in the size of the Ni nanoparticles and improved Ni dispersion. Using the Ni-Ce/SiO2 catalyst the WHSV could be increased up to 20.0h−1 while still maintaining its good catalytic activity. At this high WHSV of 20.0 h-1, the Ni/SiO2 catalyst without the ceria promoter and the Rh catalyst showed severe deactivation due to the formation of surface carbon deposits.

Ce promoted V2O5 catalyst in oxidation of SO2 reaction

Harmful environmental effects of SO2 on the start-up of the sulfuric acid plant process motivated studying ceria as a promoter for V2O5 catalyst that is employed in SO2 oxidation. Effects of SO2(%), ceria percentage, temperature and O2/SO2 were investigated to optimize ceria loading on V2O5 catalyst. To determine the main and interaction effects, a full factorial design of experiments including 315 experiments was used. The results showed that the catalyst with 7wt% ceria (VaCe7) possessed the highest catalytic performance. To study the effect of more parameters on this catalyst, other 135 post-experiments with full factorial designs were performed after the optimization of Ce contents. The results revealed that mean SO2 conversion increased with increasing SO2 (%) and O2/SO2 ratio, and decreasing GHSV. Also, the maximum mean conversion was found at the reaction temperature of 450°C by the trade-off of kinetic and thermodynamic factors of the reversible exothermic reaction. VaCe7 was found to have more catalyst activities than that the without-ceria (VaCe0) case. The synthesized catalysts were characterized by XPS, BET, FTIR, SEM, XRD and ICP. The SEM mapping revealed that the cerium oxide had better distribution on VaCe7 than VaCe9&11. FTIR, XRD and XPS showed the presence of CeVO4 in the Ce-promoted catalyst and confirmed that ceria promotes V2O5 by the formation of CeVO4 network, reduces the activation energy of reduction–oxidation and increases the rate of SO2 oxidation reaction. The stability tests demonstrated good catalytic performance stability of the synthesized catalyst up to 50h in the reaction. Results at the initial times of the stability tests showed that the catalyst with ceria promoter (VaCe7) had higher activity than VaCe0 at the start-up time. Also, VaCe7 had higher activity at the start-up than its normal conditions, which could be related to the good oxygen storage capacity of ceria because the catalyst at the start-up is faced to the oxygen of air. This high startup activity caused to use it in starting up of sulfuric acid plants that decreases SO2 emission to the environment.

Ce-promoted Co/Al2O3 catalysts for Fischer–Tropsch synthesis

The effect of ceria promotion on the performance of Co/Al2O3 catalyst was evaluated in a high pressure fixed bed reactor for Fischer–Tropsch (FT) synthesis at close industrial conditions. Ce–Al2O3 supports with a molar ratio of Al/Ce = 8 were prepared by two different methods: one by co-precipitation of cerium and aluminum precursors in water-in-oil microemulsion and the other one by aqueous impregnation of cerium nitrate on commercial alumina. These supports, together with the unmodified alumina carrier, were used to prepare four cobalt-based catalysts. These catalysts were characterized by XRD, SEM, EDX, TEM, N2 adsorption/desorption, TPR and chemisorption techniques. The results show that the presence of CeO2 on the surface of the support favors the reducibility of cobalt oxides with a shift down in reduction temperature of about 70 °C. The catalytic evaluation of the catalysts revealed that cerium addition by impregnation increases the activity and selectivity to C5+ catalyst in FTS. The catalyst synthetized by microemulsion show lower catalytic performance. Nevertheless, the catalytic property of this material can be improved by increasing the crystalline micro-domains size of CeO2.

Ceria promotion over Ni-containing hydrotalcite-derived catalysts for CO2methane reforming

The catalytic activity in dry methane reforming of hydrotalcite-derived catalysts with ceria and/or nickel species introduced into hydrotalcite interlayer spaces was examined. The prepared materials were characterized (XRF, XRD, FT-IR, H2-TPR and N2 sorption) and subsequently tested in CO2 methane reforming at 550 °C. The obtained results showed that the incorporation of nickel species between hydrotalcite layers resulted in active catalyst with no sign of carbon deposition. Additionally, a beneficial effect of ceria promotion was observed. Ceria-promoted sample exhibited higher activity, stability and selectivity towards DRM, which may be explained by the formation of small Ni crystallites and prevention of the formation of inactive NiAl2O4 spinel phase.

Renewable hydrogen production from chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers in a fixed-bed reactor

Chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers was carried out at 650 °C under atmospheric pressure in a fixed-bed reactor. The mesoporous support SBA-15 was synthesized via hydrothermal method and the xCeNi/SBA-15 oxygen carriers were prepared by encapsulating CeO2 and NiO nanoparticles in SBA-15 using surfactant-assisted iso-volumetric impregnation method. Some techniques were conducted to characterize the oxygen carriers, including N2 adsorption–desorption, XRD, TEM, H2-TPR, ICP-OES, and DSC-TGA. It was observed that all the oxygen carriers exhibited high specific surface area (>435 m2/g) and large pore volume (>0.64 cm3/g). Small NiO particle size (e.g. 3.2 nm for 12CeNi/SBA-15), high dispersion and strengthened metal-support interaction were achieved by the CeO2 promotion. The ceria promoter not only inhibited the coke formation but facilitated the removal of coke deposition, and the coke deposition could be further eliminated in the air feed step, both of which resulted in long-term stability. Meanwhile, superior redox performance and shorter ‘dead time’ (e.g. 30 s for 12CeNi/SBA-15) were achieved on account of easier reducibility of NiO particles with increasing amount of CeO2. The oxygen carriers exhibited superior sinter resistance capacity and high activity and stability in CLSR process. The highest ethanol conversion (90.0%) and hydrogen selectivity (84.7%) were obtained for 12CeNi/SBA-15 even after 14 cycle stability test.