CeO2 Loading Research Articles

Mechanistic and DFT studies on the degradation of metronidazole by cerium oxide-loaded iron-cobalt layered double hydroxide-activated calcium sulfite

In this study, Co3Fe-LDHs loaded with CeO2 were synthesized via a hydrothermal method, and the synthesized Co3Fe-LDHs@CeO2 exhibited excellent surface properties and structural stability. Moreover, Co3Fe-LDHs@CeO2 was first applied to activate CaSO3 for metronidazole (MNZ) degradation. The effects of the catalyst preparation ratio, initial pH, and coexisting substances in the system on MNZ degradation were investigated. At an initial pH of 7.0, when 0.2 g/L Co3Fe-LDHs@CeO2 and 2 mM CaSO3 were combined, 99 % of the MNZ at a concentration of 20 mg/L was eliminated in 60 min. The experimental results revealed the rapid activation of CaSO3 on the catalyst surface, where Ce plays a key role in the redox cycle between Co and Fe atoms. The loading of CeO2 enhanced the catalytic performance of Co3Fe-LDHs, as confirmed by density functional theory (DFT) calculations. The loading of Ce promoted the chemisorption of CaSO3 on the surface of Co3Fe-LDHs@CeO2, leading to the transfer of 1.48 electrons from sulfite to Co3Fe-LDHs@CeO2. These findings were consistent with the results of the electrochemical tests. SO4•- and •OH were identified as the primary active substances through electron paramagnetic resonance (EPR) and chemical probe experiments, accounting for 60.73 % and 32.81 %, respectively. By combining LC–MS and DFT calculations, three potential degradation pathways of MNZ were identified, with the intermediates found to be either nontoxic or have low toxicity. Even after being recycled five times, MNZ still showed 88 % degradation, demonstrating its exceptional reusability. Co3Fe-LDHs@CeO2 shows great potential for practical use in treating antibiotic wastewater due to its outstanding catalytic properties, anti-interference ability, reusability, and stability.

Optimization of greenhouse gas valorization over ceria‐promoted Co–Ni/graphene oxide catalytic materials using response surface methodology

AbstractBackgroundThe mitigation of global warming effect requires intensified research efforts to reduce greenhouse gas emissions. This study was aimed at investigating the valorization of two principal greenhouse gases, namely carbon dioxide (CO2) and methane (CH4), over CeO2‐doped Co–Ni/GO catalytic materials. The CeO2‐doped Co–Ni/GO catalysts were synthesized using a sequential wet impregnation method and employed for CO2 reforming of CH4. The catalytic materials were characterized using various instrumental techniques. Response surface methodology (RSM) was employed to investigate the impact of process factors, namely reaction temperature (ranging from 700 to 800 °C), CeO2 loading (ranging from 5% to 15%) and feed flowrate (ranging from 10n to 50 mL min−1), on the CH4 conversions.ResultsThe three factors were observed to have significant influence on the CH4 conversion based on analysis of variance. The analysis of the RSM quadratic model revealed that the optimum conditions of 800 °C, 14.22% and 10.00 mL min−1 were obtained for the reaction temperature, CeO2 loading and feed flowrate resulting in maximum CH4 conversion of 98.24%. The desirability function for these results was calculated to be 0.934. The predicted process parameters aligned with the results of the actual experimental analysis.ConclusionThis study has demonstrated that the conversion of CH4 to value‐added products such as syngas can be optimized using RSM. The optimum conditions obtained could be used to improve the process performance. © 2024 Society of Chemical Industry (SCI).

Preparation of ZIF-67 derived Co3O4 composite non-homogeneous catalysts with cerium oxide for the efficient degradation of Rhodamine B

The textile printing and dyeing industry produces a significant amount of wastewater, which is challenging to degrade due to its high organic concentration, complex composition, and high chromaticity. This type of wastewater is considered one of the most difficult to treat. In recent years, advanced catalytic oxidation based on sulfate radicals (SO4−) can efficiently degrade printing and dyeing wastewater. Seeking non-homogeneous catalysts for the activation of the radicals is the key problem to be solved nowadays. In this study, Ce/Co-ZIF precursor was obtained by stirring and precipitation, and the ZIF-67-derived non-homogeneous catalyst of Co3O4 and CeO2 was successfully synthesised by calcination for the efficient catalytic degradation of Rhodamine B (RhB) dye. The morphological structure and elemental distribution of the non-homogeneous catalysts were observed using SEM, TEM, XRD, and XPS. Additionally, the factors that affect the degradation of RhB dye were investigated. These factors were adjusted individually, from CeO₂ loading, pH, material dosing, to persulfate (PS) dosing, and it was determined that the rate of RhB degradation also increased from the initial 92 % to a value of 97.1 %. It was found that under the optimal conditions of a CeO2 loading percentage of 0.44, pH of 7, and composite material and potassium persulfate dosage of 5 mg and 0.4 g/L, respectively, the catalytic system achieved a degradation rate of 97.5 % of RhB dye within 30 min. Then the non-homogeneous catalyst could still maintain the good catalytic degradation effect after 5 cycles of regeneration experiments. Therefore, the ZIF-Co3O4@CeO2 non-homogeneous catalyst has a good potential for wastewater treatment and provides a new way for the application of high performance catalysts in the future.

Hydrogen Storage Using Platinum‐Supported Ceria Dispersed on Activated Carbon

ABSTRACTIn the current work, carbon materials were used in the hydrogen adsorption process, specifically as carbons doped with platinum dispersed on ceria. The textural characterization results of the prepared samples and the starting carbon showed the presence of both micro‐ and mesopores. On the other hand, it has been observed that the specific areas were inversely proportional to the CeO2 loading. In addition, the amount of adsorbed hydrogen increased after doping the carbon with platinum and, even more, when the carbon was doped with Pt dispersed on ceria (2.2 mg/g at 25°C and 30 bar). However, there was a ceria optimum from which the adsorption capacity decreased (10% wt). The results of temperature‐programmed desorption (TPD) of hydrogen indicated a high affinity between Pt and H2 that enhanced H2 adsorption process by establishing chemical bonds between the metal particles and H2. Precisely, the presence of metallic Pt particles dispersed on ceria considerably promotes the spillover process of hydrogen on carbon. This can be confirmed by hydrogen adsorption–desorption isotherms, that showed that complete desorption of chemisorbed hydrogen required an increase of temperature.

Synthesis of CeO2 Coupling rGO Material Oriented to Rhodamine B Degradation under Optical Irradiation

In the present work, CeO2 with different loading were embedded on reduced graphene oxide (rGO) by a simple one-pot hydrothermal method. The synthesized samples were characterized using XRD, EDX mapping, FESEM and UV-Vis DRS techniques. The photocatalytic activity of the as-synthesized CeO2, rGO, and 0,5% (1,5% and 5,0% wt )CeO2/rGO was studied by monitoring the degradation of Rhodamine B dye (denotes RhB) under xenon light irradiation. The analyses show that CeO2 particles were evenly dispersed on rGO and the optical properties of the xCeO2/Rgo (x = 0,5; 1,5; and 5,0%wt)/rGO material were significantly enhanced due to the interaction between CeO2 anf rGO. The effects of CeO2 loading, initial RhB concentration and pH were thoroughly investigated. Under the irradiation, the RhB degradation reached 100% over 1.5%CeO2/rGO. tThe high performance of the synthesized composites was attributed to the significant suppression of the recombination rate of photo-generated electron - hole pairs due to charge transfer between rGO sheets and CeO2 particles and the smaller optical band-gap in the CeO2/rGO nanocomposite.

Experiments and mechanism of kinetics/stability of CO2 capture by Ce/Zr carrier-loaded MgO-based adsorbents

Magnesium oxide (MgO) has demonstrated tremendous potential in carbon capture and utilization (CCU) technology. However, it still faces limitations such as low adsorption kinetics and poor stability. In this study, the sol–gel combustion method was employed to synthesize MgO/molten salt composite adsorbents supported on Ce/Zr carriers. The investigation focused on the influence of carrier composition on adsorption performance. The experimental results revealed that as the loading of CeO2 increased, the adsorbent materials transitioned from a porous foam-like connectivity to the formation of a shell structure. Interestingly, the low content of CeO2 facilitated enhanced CO2 diffusion and hindered the aggregation of MgO aggregates, resulting in improved adsorption performance. Furthermore, the adsorbents supported on ZrO2 demonstrated excellent particle size stability and cyclic stability due to the higher Tamman temperature of ZrO2 and the uniform dispersion of MgO on ZrO2. Utilizing density functional theory, a surface configuration of CeO2/ZrO2 catalyst-modified MgO (100) was constructed to elucidate the enhanced adsorption mechanism of CeO2/ZrO2 on MgO. The cluster model revealed a strong interaction between cluster O atoms and CO2 molecules, enhancing the charge transfer capability of the MgO surface towards CO2 and consequently strengthening its adsorption performance.

Facile synthesis of nano CeO2/sepiolite composite as visible-light-driven photocatalyst for rapid tetracycline removal

A novel CeO2/sepiolite (CeO2/SEP) composite with sepiolite as the support of CeO2 was successfully prepared using a simple ammonia precipitation method for the photocatalytic degradation of tetracycline (TC) by loading CeO2 nanoparticles on sepiolite. The analytical results showed that CeO2/SEP had good crystallization, and CeO2 nanoparticles were deposited on the surface of fibrous sepiolite. The composite photocatalyst with 50 % CeO2 loading presented the highest tetracycline degradation efficiency (92.7 %), and the reaction rate constant was 4.88 times greater than that of pure CeO2. In addition, quenching experiments showed that the main reactive active species included photogenerated holes (h+) and superoxide radical anions(O2·-).Furthermore, the enhanced photodegradation mechanisms and the possible degradation pathways of TC were also systematically discussed. The investigating results show that the enhanced photocatalytic performance was mainly due to the uniform attachment of CeO2 with smaller particle size on the surface of sepiolite, which increased the specific surface area of the photocatalyst and promoted the redox cycle of Ce3+/Ce4+ to generate more reactive free radicals. It can be concluded that this study offers a new potential option for efficient photodegradation of antibiotics in wastewater based on the visible-light-driven mineral based photocatalyst.

Synthesis of CeO2-loaded composite catalysts of ZIF-67 for activation of persulfate degradation of Congo red dye

One of the most widely used and promoted synthetic dyes in the world is azo dyes, and the treatment of azo dyes wastewater is a hot issue. Currently, advanced oxidation technology is able to treat dye wastewater efficiently and the most critical means is to seek for suitable catalysts to activate the free radicals. In this study, ZIF-67@CeO2 composites were successfully synthesised by heating and refluxing and it degraded Congo red dye by activation of persulfate. The morphological structure of the composites was observed by using SEM, TEM, XPS, XRD, FT-IR and BET characterisation. In addition, the effects of different factors on the degradation of Congo red dye by the catalytic system were studied. And it was found that the best catalytic effect could be achieved at pH = 7, CeO2 loading of 0.3 g, and composite and potassium persulfate dosage of 10 mg and 0.3 g/L, respectively, and the degradation rate of the Congo red dye reached 98.8 %. Furthermore, the composite was able to maintain a better catalytic degradation effect after 4 cycles of regeneration experiments. Therefore, the ZIF-67@CeO2 composite as a new catalyst has a good application prospect in water treatment, which opens up a new avenue for the development of high-performance catalysts.

Facile synthesis of multi-layer Co(OH)2/CeO2-g-C3N4 ternary synergistic heterostructure for efficient photocatalytic oxidation of NO under visible light

In this work, we report a one-step synthesis of ternary Z-scheme Co(OH)2/CeO2-g-C3N4 (CoCe-CN) heterostructure via hydrothermal method. Owing to the modification of Co(OH)2 and CeO2, the existence of Co(OH)2 as an electron acceptor-donor center between CeO2 and g-C3N4 accelerates the electron transfer and provides extra OH- reaction pathway for photocatalytic oxidation of NO. As a result, 50CoCe-CN (Co and Ce accounting for 25% mass ratio separately) achieved a 53.5% conversion efficiency of NO at 600 ppb concentration, which is 1.82 times that of g-C3N4 under visible light. The results of the DFT analysis and element distribution of cobalt and ceria provide convincing evidence supporting the existence of a novel multi-layer structure in the CoCe-CN photocatalyst. This structure involves the loading of CeO2 and Co(OH)2 on the g-C3N4 surface, and Co(OH)2 as a co-catalyst introduced between CeO2 and g-C3N4 realizes the synergy between CeO2 and Co(OH)2 which further improve the photocatalytic properties. The higher photocatalytic efficiencies observed in the CoCe-CN photocatalysts compared to those containing only cobalt (Co-CN) or ceria (Ce-CN) provide further evidence of the synergistic effect of these two elements. This work demonstrates a more efficient and effective ternary photocatalytic system, with greater practical potential for photocatalytic oxidation of NO.

Influence of CeO2 on glass formation, structural and thermal properties of sodium niobium phosphate glass

Cerium is a well-known surrogate to trivalent and tetravalent actinides and has been investigated to explore the structural and thermal characteristics of simulated radwaste-loaded material systems. The solubility and distribution of CeO2 into a sodium niobium phosphate glass have been explored with the objective of developing a host matrix for radioactive waste immobilization. Niobium phosphate glasses of (100-x) (40Na2O–20Nb2O5–40P2O5)-xCeO2 (x = 0, 1, 3, 5, 8, and 10 mol%) compositions are prepared by melt-quenching method and are characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). This study summarises the influence of cerium ion incorporation on the structure, thermal stability, and formation of crystalline phases of the niobium phosphate glass. The various glass stability parameters, such as Hruby (KH), Weinberg (KW), and Lu–Liu (KLL) parameters are estimated to assess the stability of the glass melt against devitrification in the supercooled region. The spectroscopic analysis ascertains the presence of metaphosphate and pyrophosphate networks as primary structural building units in the glass. However, the Raman analysis demonstrates the influence of CeO2 on the network linkages arising from the corner-sharing of NbO6 octahedrons and Nb–O–P bonding in the glass. The CeO2 loading is optimized up to 8 mol% into the base 40Na2O–20Nb2O5–40P2O5 glass matrix without precipitation of any crystalline phase. The glasses are heat treated to obtain glass-ceramics embedded with the crystalline phases, namely, monazite CePO4, NbOPO4, NaNbO3, and niobium phosphate bronze Na6Nb8(PO4)5O15. The microanalysis of these glass ceramics shows that the CeO2 is more aggregated inside the niobium phosphate bronze framework than in the bulk at a higher temperature. It is also observed that the surface crystallization process is a prevalent mechanism for the crystallization of glasses on heating at crystallization onset temperature.

Process simulation and reaction performance evaluation of CO2 chemical looping conversion based on modified bauxite residue oxygen carriers

A large number of greenhouse gas emissions have brought a series of environmental problems, so it is urgent to realize efficient conversion of CO2. The multistage regeneration process of CO2 chemical looping conversion was established and the process simulation analysis carried out with Aspen Plus. The system’s feasibility was verified by simulation and the process needed to provide additional energy input, and the sensitivity analysis of different operating conditions was carried out to provide guidance for subsequent experimental design. Oxygen carrier bauxite residue was modified by acid washing and CeO2 impregnation, and the reaction characteristics were evaluated via a fixed-bed reactor and on-line mass spectrometry, and the kinetic parameters of the reaction were solved by gas-solid reaction kinetics. The results showed that 12 wt% CeO2 loading oxygen carrier had the highest yield and average formation rate of CO, which were 6.22 mmol·g−1 and 388.71 μmol·g−1·min−1, respectively. The oxygen carrier conversion (oxygen vacancy utilization) was close to 100% after modification, while that of single bauxite residue oxygen carrier was only 60%. The reaction system conformed to the first-order reaction model, and the activation energy was 33.90 kJ·mol−1. This study provided new insight into chemical looping conversion of CO2.

Free occupying mechanism of simulated tetravalent waste ions in Gd2Zr2O7 and performance evaluation of the waste forms

AbstractTo extend the practicability of ceramics in immobilizing nuclear waste with fluctuant composition, structural design should be abandoned. The simulated tetravalent actinide waste An4+ (Ce4+) was directly doped into prepared Gd2Zr2O7, and the waste forms were synthesized by high‐temperature solid‐state reaction. It has been shown that the maximum loading of CeO2 in Gd2Zr2O7 lies between 20 and 30 wt.%, and Ce elements are uniformly distributed in the matrix. Existing in Ce3+ and Ce4+, cerium ions automatically occupied both the Gd and Zr sites in Gd2Zr2O7 according to valence equilibrium. This occupation causes the change of r(A3+)/r(B4+) and eventually leads to the structure transition from pyrochlore to fluorite. In addition, the normalized leaching rate of the sample with 60 wt.% of dopant was about 2.5 × 10−7 g m−2 d−1 on the 35th day. In this study, a free occupation of simulated waste ions in ceramics was proposed.

Facile synthesis of Z-scheme CeO2@AgBr heterojunction for improved dye degradation

CeO2 nanorods were synthesized by the hydrothermal method and coupled with AgBr via deposition approach. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and diffuse reflection spectroscopy (DRS) were used to characterize the structure, morphology and optical properties of the samples. The photoinduced charge separation efficiency was determined by transient photocurrent response and photoluminescence (PL) spectra. The effect of CeO2 loading on the Rhodamine B (RhB) degradation in CeO2@AgBr composites was also investigated. The results indicated that 40 wt%-CeO2@AgBr photocatalyst demonstrated the highest photocatalytic activity than pure CeO2 and AgBr. The trapping experiment showed that holes (h+) and superoxide radicals (•O2−) were the main active species for the degradation of RhB. The improved photocatalytic activity of CeO2@AgBr catalysts were attributed to the formation of Z-scheme heterojunction, which effectively inhibited the recombination of photoinduced electron-hole pairs.

Directly synthesis of dimethyl carbonate from CO2 and methanol over UiO-66 @CeO2 Catalyst

In this study, UiO-66 @CeO2 composites was prepared by loading CeO2 nanoparticles on the surface of UiO-66 using precipitation method, and the effect of CeO2 loading on the catalytic direct reaction of CO2 and methanol into dimethyl carbonate (DMC) was investigated. XRD, N2 adsorption-desorption, FT-IR, XPS, SEM and TEM were used to investigate the physical and chemical properties of UiO-66 @CeO2. The results showed that the framework structure of UiO-66 benefit the high dispersion of CeO2, while the loading of CeO2 provided more oxygen vacancies, which promoted the capture and absorb of CO2, thus promoted the reaction synergistically. Among which, UiO-66 @CeO2-60 showed best activity, with the highest DMC formation rate of 2.84 mmol·g−1·h−1 (yield: 2.27%) within 4 h of reaction time under the optimum conditions. In addition, the catalyst also showed favorable reusability, maintaining ∼90% of catalytic efficiency with 4 reuse cycles compared the fresh ones.

Efficient photothermal conversion for oxidation removal of formaldehyde using an rGO-CeO2 modified nickel foam monolithic catalyst

Photocatalysis is a feasible method for degrading indoor formaldehyde (HCHO) pollutants. To improve the purification efficiency and lower the cost of using noble metals as the primary component of the catalyst, synergistic catalysis involving two catalytic modes, such as thermocatalysis/photocatalysis, has attracted significant attention. In this study, a monolithic catalyst was prepared by loading reduced graphene oxide (rGO) and cerium dioxide (CeO2) on a nickel foam (NF) matrix. It was observed that the HCHO removal efficiency could be > 93 % under xenon light. The pre-deposited rGO on the NF matrix served as the photothermal conversion layer and contributed to the uniform and stable loading of CeO2. The surface temperature of this synthesized monolithic catalyst could rapidly rise to 170 °C. In addition, the heat was distributed evenly because of the increased near-infrared (NIR) light absorption caused by the added rGO and high electron mobility owing to the heat-conducting property of NF. At this temperature, the oxidation of HCHO was stimulated not only by the lattice oxygen of CeO2 but also by the production of O2– via oxidation by photogenerated electrons. In addition, O2– would reoxidize Ce3+ to Ce4+ on oxygen vacancies and accelerate the lattice oxygen consumption and supply cycle to reinforce the existing Mars-van Krevelen (MvK) mechanism.

In-situ synthesis of 0D/1D CeO2/Zn0.4Cd0.6S S-scheme heterostructures for boosting photocatalytic remove of antibiotic and chromium

The development of green and efficient photocatalytic materials for the treatment of medical and industrial wastewater has become a current research focus. In this work, the CeO2/Zn0.4Cd0.6S heterojunction with a special 0D/1D morphology was synthesized by a soft chemistry method. The successful construction of the heterojunction was verified by the binding energy migration of XPS and TEM. The photocatalytic activities were determined by photoreduction of hexavalent chromium ions (CrVI) and photodegradation of tetracycline hydrochloride (TC). The experimental results showed that the loading of CeO2 significantly improves the photocatalytic performance of Zn0.4Cd0.6S, and the loading of 10 wt% CeO2 has the best photocatalytic activity and structural stability. The S-scheme electron transport mechanism was particularly investigated through active species trapping experiments. This work provides an effective idea for the design of highly stable metal sulfide photocatalysts.

Co-catalyst free direct Z–scheme photocatalytic system with simultaneous hydrogen evolution and degradation of organic pollutants

Photocatalytic hydrogen evolution coupled with simultaneous pollutant degradation is a promising but challenging strategy for both wastewater treatment and renewable energy production. In this work, a series of direct Z-scheme heterostructural catalysts, denoted as CeO2/Cu–I-bpy, were designed and constructed by in-situ synthesizing CeO2 nanoparticles on the surface of a coordinate polymer, named Cu–I-bpy. The simultaneous photocatalytic evolution of hydrogen and photo-degradation of organic pollutants was successfully achieved with this hybrid catalyst, even without any co-catalyst. The hybrid catalyst exhibited a 6.9 folds higher hydrogen evolution efficiency than the corresponding individual photo-reduction catalyst (Cu–I-bpy here), and 2.5 times degradation rate of the corresponding individual photo-oxidation catalyst (CeO2 here), after optimizing the CeO2 loading. After extensively characterized via XRD, XPS, Raman spectroscopy, UV–Vis absorption spectroscopy, SEM, TEM, BET, photo-electrochemical method and photoluminescence, it was found that the hybrid catalysts show higher charge separation and transfer efficiency than corresponding individual CeO2 and Cu–I-bpy. Further mechanism investigation via active species trapping, EPR and electron flow experiments indicates a direct Z-scheme charge transfer mechanism in the CeO2/Cu–I-bpy, which not only boosts the photogenerated electron-hole separation efficiency, but also retains the high reduction and oxidation ability the corresponding individual catalyst for hydrogen evolution and pollutant degradation, respectively. This work demonstrates the possibilities of turning waste water into energy resources using carefully designed photocatalytic systems.

Thermal Catalytic Decomposition of Dimethyl Methyl Phosphonate Using CuO-CeO2/γ-Al2O3

Chemical warfare agents (CWAs) are highly toxic and fast-acting and are easy to cause large-scale poisoning to humans and livestock after being released. The activated carbon used for CWAs adsorption has disadvantages of limited adsorption capacity, easy aging and deactivation. Metal oxides have environmental stability, and they are characterized by long lasting and broad spectrum when used for thermal catalytic decomposition. Therefore, in this study, the supported copper–cerium catalyst CuO-CeO2/γ-Al2O3 was prepared using an equal volume impregnation method. The thermal catalytic decomposition performance was studied using sarin CWAs simulant dimethyl methyl phosphonate (DMMP) as the target compound. The results show that the CuO-CeO2/γ-Al2O3 catalyst with a CeO2 loading of 5% exhibited better thermal catalytic decomposition performance of DMMP. The catalyst provided protection against DMMP for 237 min at 350 °C; CuO was highly dispersed on CuO-5% CeO2/γ-Al2O3, and there was a strong interaction between Cu and Ce on CuO-5% CeO2/γ-Al2O3, which promoted the generation of surface-adsorbed oxygen, leading to a better thermal catalytic decomposition performance of DMMP. This study is expected to provide a reference for the study of catalysts for the thermal catalytic decomposition of CWAs.

Hydrodesulfurization of Dibenzothiophene over Ni-Mo-W Sulfide Catalysts Supported on Sol-Gel Al2O3-CeO2.

To achieve sulfur content in gas oil at a near-zero level, new catalysts with improved hydrogenation functions are needed. In this work, new Ni-Mo-Mo hydrodesulfurization (HDS) catalysts supported by Al2O3-CeO2 materials were synthesized to evaluate their efficiency in the reaction of HDS with dibenzothiophene (DBT). Al2O3-CeO2 supports different CeO2 loadings (0, 5, 10 and 15 wt.%) and supported NiMoW catalysts were synthesized by sol-gel and impregnation methods, respectively. The physicochemical properties of the supports and catalysts were determined by a variety of techniques (chemical analysis, XRD, N2 physisorption, DRS UV-Vis, XPS, and HRTEM). In the DBT HDS reaction carried out in a batch reactor at 320 °C and a H2 pressure of 5.5 MPa, the sulfide catalysts showed a dramatic increase in activity with increasing CeO2 content in the support. Nearly complete DBT conversion (97%) and enhanced hydrogenation function (HYD) were achieved on the catalyst with the highest CeO2 loading. The improved DBT conversion and selectivity towards the hydrogenation products (HYD/DDS ratio = 1.6) of this catalyst were attributed to the combination of the following causes: (i) the positive effect of CeO2 in forcing the formation of the onion-shaped Mo(W)S2 layers with a large number of active phases, (ii) the inhibition of the formation of the undesired NiAlO4 spinel phase, (iii) the appropriate textural properties, (iv) the additional ability for heterolytic dissociation of H2 on the CeO2 surfaces, and (v) the increase in Brønsted acidity.

Effect of CeO2 on carbon deposition resistance of Ni/CeO2 catalyst supported on SiC porous ceramic for ethanol steam reforming

Ni/CeO2 catalysts (nCeO2:nNi = 0, 1, 4, 7, 10) supported on SiC porous ceramics for ethanol steam reforming (ESR) were investigated with respect to hydrogen production performance and growth of carbon deposition. The oxygen released from CeO2 enables the oxidation of CHx species to serve as carbon precursors, thus providing Ni/CeO2 catalysts with stronger resistance to carbon deposition compared with Ni catalysts. The Ni/CeO2 catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics. Under 500 °C for 25 h of ESR reaction, the ethanol conversion rate over Ni/CeO2 catalysts (nCeO2:nNi = 7) is sustained up to 100% and H2 selectivity is essentially kept at 74%. The by-product selectivity declines stepwise with increasing content of CeO2, which is attributed to the adsorption and oxidation of CO and of CHx species as CH4 precursor from CeO2. The scanning electron microscopy (SEM) and transform electron microscopy (TEM) results reveal that further loading of CeO2 on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles. Furthermore, carbon deposition on Ni/CeO2 catalysts preferentially outgrow filamentous rather than amorphous carbon, with a tendency for the latter to be more deactivated.