CeO2 Support Research Articles

The interparticle oxygen vacancies enrichment in the matrix of fibrous silica ceria supported nickel for CO methanation

Aspherical nickel-loaded fibrous silica mesoporous ceria (Ni/FSCe) with a cockscomb-like structure has been synthesized using a microemulsion technique integrated with a crystal-seed crystallization process and unprecedently utilized for CO methanation. Numerous systems were used to characterize the catalysts systematically. The Ni/FSCe showed greatly enhanced catalytic capability with the CO conversion of 95.67 % and the CH4 yield of 91.20 % at 400 °C, which is higher than that of the nickel-ceria loaded onto conventional KCC-1 (Ni-Ce/KCC-1). Furthermore, it demonstrated excellent stability, with no indication of deactivation for 75 h. Numerous factors, including the synergistic effect of high amount of inter-nanoparticle oxygen vacancies which lead towards high basicity and well-dispersed Ni, which act as both carbon monoxide and hydrogen adsorption sites, are considered to be responsible for the significant improvement in CO methanation. The superiority in the activity and stability of Ni/FSCe over Ni-Ce/KCC-1 also could be attributed towards better metal-support interactivity between the Ni nanoparticles and CeO2 support, which helps to inhibit crystallite migration and provides protection against carbon deposition. Core-shell FSCe, with their high catalytic characteristics, imply significant application potential in basic-catalyzed reactions, particularly methane generation.

Enhanced selective hydrogenation of glycolaldehyde to ethylene glycol over Cu0-Cu+ sites

Selective hydrogenation of hydroxyaldehydes to polyalcohols is challenging due to the competitive hydrogenation of CO and CO. This study develops heterogeneous Cu catalysts for the selective synthesis of ethylene glycol via batch liquid-phase hydrogenation of glycolaldehyde. SiO2 supported Cu, fabricated by ammonia evaporation, enables to catalyze the CO bond hydrogenation with retaining the CO bond intact, yielding higher selective hydrogenation activity with ethylene glycol selectivity up to 99.8 % relative to MgO, Al2O3, CeO2, and TiO2 supports and Cu/SiO2 synthesized by deposition–precipitation and impregnation. Characterizations confirm that highly efficient 20Cu/SiO2-AE-623 K catalyst fabricated by ammonia evaporation is featured with larger Cu0 and Cu+ surface areas, of which the Cu+ species created from reducing copper phyllosilicate exhibit higher reactivity. A synergistic effect between Cu+ and Cu0 facilitates the selective adsorption/activation of glycolaldehyde on Cu+ sites and the dissociation of H2 on Cu0 sites, bringing a remarkable improvement in the selective hydrogenation performance.

Intuitive study on the effect of support morphology over Cs-Ru/CeO2 catalyst for microwave-initiated ammonia synthesis

Microwave-initiated ammonia synthesis is a potential candidate to the current Haber-Bosch process that can operate from stranded renewable energy source. Our previous studies indicated Cs-Ru/CeO2 is a promising catalyst for microwave-assisted ammonia synthesis and the morphology of CeO2 significantly affects the catalytic performance. In this paper, CeO2 support with distinct morphologies nanorod, nanoparticle, and microstructure, is studied comprehensively at ambient pressure and low temperature under microwave irradiation. Moreover, CeO2 nanorods of various sizes were synthesized at different timing (24, 36, and 48 h). Nanorods synthesized at 36 h exhibited superior activity associated to high dispersion and small Ru particle size.

Intermediate temperature exposure regenerates performance and active site dispersion in sintered Pd–CeO2 catalysts

Methods that can impede or reverse the effects of high-temperature sintering and deactivation are necessary to improve the utilization of catalytic materials. This work demonstrates that exposure to intermediate temperatures (800 °C) can effectively regenerate catalytic performance in sintered Pd-CeO2 catalysts, through the disintegration and partial redispersion of agglomerated Pd, which increases the abundance of sites that interface strongly with the CeO2 support. Pretreating the catalyst at 800 °C before sintering forms highly dispersed Pd species that slow the sintering of small, polycrystalline CeO2 domains. This preserves the density of Ce3+ sites that trap mobile Pd, which improves the efficacy of regeneration. The regenerated catalyst is effective in the co-oxidation of CO and C3H8, two species which are known to competitively adsorb. The simplicity of this treatment makes it attractive for on-stream regeneration of catalyst performance.

The tuned selective catalytic reduction behaviors of NO over the Pt/CeO2 catalysts by preferentially exposing different facets of CeO2 supports

For the Pt catalysts supported on CeO2 nanosheet (NS), nanopolyhedron (NP) and nanorod (NR) with preferentially exposed {100}, {111} and {110} facets, respectively, the NO conversion and N2 selectivity for NO + CO reaction at 100–250 °C exhibit the order as Pt/CeO2-NS{100} > Pt/CeO2-NP{111} > Pt/CeO2-NR{110}. The higher surface concentration of oxygen vacancies on CeO2 (NS) can promote the dissociation of NO and result in the highest performance of Pt/CeO2-NS{100} catalyst. Moreover, CO intensively chemisorbs on the Pt2+ ions on CeO2 (NR) support, suppressing the dissociative chemisorption of NO and leading to lower reaction performance of Pt/CeO2-NR{110} catalyst.

Ti‐doped CeO2 Stabilized Single‐Atom Rhodium Catalyst for Selective and Stable CO2 Hydrogenation to Ethanol

AbstractDevelopment of effective and stable catalysts for CO2 hydrogenation into ethanol remains a challenge. Herein, we report that Rh1/CeTiOx single‐atom catalyst constructed by embedding monoatomic Rh onto Ti‐doped CeO2 support has shown a super high ethanol selectivity (≈99.1 %), record‐breaking turnover frequency (493.1 h−1), and outstanding stability. Synergistic effects of Ti‐doption and monoatomic Rh contribute to this excellent catalytic performance by firstly facilitating oxygen vacancies formation to generate oxygen‐vacancy‐Rh Lewis‐acid‐base pairs, which favor CO2 adsorption and activation, cleavage of C−O bonds in CHxOH* and COOH* into CHx* and CO* species, subsequent C−C coupling and hydrogenation into ethanol, and secondly generating strong Rh−O bond by Ti‐doping‐induced crystal reconstruction, which contributes to striking stability. This work highlights the importance of support elaborating regulation for single‐atom catalyst design to substantially improve the catalytic performance.

Ti-doped CeO2 Stabilized Single-Atom Rhodium Catalyst for Selective and Stable CO2 Hydrogenation to Ethanol.

Development of effective and stable catalysts for CO2 hydrogenation into ethanol remains a challenge. Herein, we report that Rh1 /CeTiOx single-atom catalyst constructed by embedding monoatomic Rh onto Ti-doped CeO2 support has shown a super high ethanol selectivity (≈99.1 %), record-breaking turnover frequency (493.1 h-1 ), and outstanding stability. Synergistic effects of Ti-doption and monoatomic Rh contribute to this excellent catalytic performance by firstly facilitating oxygen vacancies formation to generate oxygen-vacancy-Rh Lewis-acid-base pairs, which favor CO2 adsorption and activation, cleavage of C-O bonds in CHx OH* and COOH* into CHx * and CO* species, subsequent C-C coupling and hydrogenation into ethanol, and secondly generating strong Rh-O bond by Ti-doping-induced crystal reconstruction, which contributes to striking stability. This work highlights the importance of support elaborating regulation for single-atom catalyst design to substantially improve the catalytic performance.

Enhanced radical generation and utilization efficiency by interfacial enrichment and electronic regulation of CuMnO2/CeO2: Processes and mechanism

As a radical predominant reaction, how to enhance the generation and utilization efficiency of radical through interface regulation then to improve its catalytic activity has been the long-term goal to promote its practical application. Realized the redox carrier may play multifunctional roles in catalytic reaction, CeO2 supported CuMnO2 (CuMnO2/CeO2) was successful constructed and the catalytic performance, reaction process and the relevant mechanism were compared with its simple physical mixed form (CuMnO2 + CeO2). It was found that the introduction of CeO2 provided a large specific surface area to strengthen the enrichment of pollutants at the interface (10 % vs 5 % for ofloxacin and 32 % vs 27 % for tetracycline hydrochloride). In addition, the activated CeO2 support enhanced the interfacial electron transfer process and promoted the generation of more highly active Ce3+ in CuMnO2/CeO2. Their synergistic effects shortened the migration distance from the formed radicals to target pollutants, thus improving the generation and utilization efficiency of radicals. So, the ofloxacin degradation rate in CuMnO2/CeO2 catalytic system was 3.25 times higher than that in CuMnO2 system (0.091 min−1vs 0.028 min−1). Moreover, the ion dissolution experiment further confirmed that the CuMnO2/CeO2 catalytic system can effectively reduce the ion dissolution, which was one of the most important parameters for practical application. Thus, this work proposes a strategy for developing high activity and environmentally friendly heterogeneous Fenton catalysts based on the principles of interface enrichment and electronic regulation.

Relationship between hydrothermal temperatures and structural properties of CeO2 and enhanced catalytic activity of propene/toluene/CO oxidation by Au/CeO2 catalysts.

A simple hydrothermal synthesis of CeO2 was implemented to obtain a series of CeO2-supported gold (Au) catalysts, used for the total oxidation of propene/toluene/CO gas mixtures and the oxidation of CO. CeO2 preparation started from a cerium hydrogen carbonate precursor using a range of different hydrothermal temperatures (HT) from 120 to 180°C. High-resolution transmission electron microscopy, X-ray diffraction, and H2-temperature-programmed reduction data indicated that CeO2 morphology varied with the HT, and was composed of the more active (200) surface. Following Au deposition onto the CeO2 support, this active crystal plane resulted in the most widely dispersed Au nanoparticles on the CeO2 support. The catalytic performance of the CeO2-supported Au catalysts for both oxidation reactions improved as the reducibility increased to generate lattice oxygen vacancies and the number of adsorbed peroxide species on the CeO2 support increased due to addition of Au. The Au catalyst on the CeO2 support prepared at 120°C was the most active in both propene/toluene/CO oxidation and independent CO oxidation.

Weakening the Metal–Support Interactions of M/CeO2 (M = Co, Fe, Ni) Using a NH3-Treated CeO2 Support for an Enhanced Water–Gas Shift Reaction

The metal–support interface plays a crucial role in heterogeneous catalysis. The modulation of the metal–support interaction (MSI) affords the possibility of promoting the catalytic efficiency per active site. Here, we report a strategy to modulate the interfacial interaction and then optimize the interfacial activity of Co/CeO2 catalysts for the water–gas shift reaction (WGSR) by a facile NH3 treatment process for the CeO2 support. The sample of Co/800N-CeO2 treated at 800 °C exhibited the highest reaction rate of 260 μmolCO/(gCo s), which was 23.8 times higher than the rate of the untreated Co/CeO2 sample. A combination of ex situ and in situ characterizations suggested that addition of the NH3 treatment process did not only weaken the metal–support interaction between the Co species and CeO2 support to strengthen CO adsorption and CO activation ability but also induced oxygen vacancy generation under reaction conditions to accelerate H2O activation. Both worked together in promoting the catalytic efficiency for the WGSR via the carboxyl pathway at a low temperature. It was worth mentioning that the N species of the CeO2 support introduced by the NH3 treatment was removed after changing the catalyst structure under reaction conditions. The interfacial structure was robust in a 60 h test at 400 °C due to the coexistence mechanism of carboxyl and formate pathways avoiding the poisoning effect of formate species on the active sites. The construction of active interfaces could be extended to Fe/CeO2 and Ni/CeO2 catalysts and could bring great promise in the design of the interfacial structure of supported catalysts in wide applications including chemical transformation reactions and industrial catalysis.

Sn auxiliary agent promoting dispersion of Pt atoms over CeO2 catalysts and DFT calculation

Highly dispersed metal nanoparticles on support are closely related to improving catalytic activity and reducing catalyst cost. Improving the dispersibility of the active components during the preparation of the catalyst is necessary for an unavoidable catalyst sintering in catalytic process. As an important catalytic system in industrial processes, Pt/CeO2 suffers from the sintering problem, therefore, there is an urgent need to improve the redispersion ability of Pt. Our work found that reverse oxygen overflow from CeO2 crystal can facilitate Pt redispersion. More importantly, introduction of Sn into the Pt/CeO2 can reduce the required temperature for Pt redispersion. The dissociation and anchoring of Pt atoms were calculated by DFT, and the redispersion mechanism of Pt on CeO2 support was explained from the perspective of thermodynamics. This work is learnable to study the redispersion of other catalysts.

Role of ZrO2 and CeO2 support on the In2O3 catalyst activity for CO2 hydrogenation

Methanol synthesis from CO2 hydrogenation has drawn global attention as catalytic CO2 hydrogenation is an attractive choice to mitigate CO2 emissions and lessen dependency on fossil resources. In the present study, we have synthesized ZrO2 and CeO2-supported In2O3 catalysts for methanol synthesis from CO2 hydrogenation and the catalytic performances of Inx/ZrO2, and Inx/CeO2 (x = 1 % and 13 %) were compared. Specifically, the effect of the ZrO2 and CeO2 supports on In2O3 catalyst during CO2 hydrogenation was explored. This study reveals that ZrO2 support increased the catalytic activity while the CeO2 support decreased although both supports have almost the same indium loading and surface area. Various characterizations like XRD, DRIFT, CO2-TPD, H2-TPR and XPS analysis of catalysts provided insight into changes that arise after mixing the two oxides and during the reaction as well as after the reaction. The stabilities of In2O3, In13/ZrO2, and In13/CeO2 were tested for up to 50 h and we found In13/ZrO2 was stable during this time-on-stream, while In13/CeO2 lost activity after 2 h of reaction. XPS results of spent catalysts showed that In(OH)3 was observed significantly over the spent In13/CeO2. OH groups were also verified by DRIFT experiments, however at low levels due to low CO2 conversion at atmospheric pressure. XRD analysis confirmed the sintering of CeO2 support during the reaction. Thus, the hydrophilic nature of CeO2, redox properties of CeO2 and sintering of CeO2 support in the presence of water, were the main reasons for the early deactivation of In13/CeO2. A regeneration study was carried out to regenerate the catalyst and the results showed that partial regeneration of the In13/CeO2 catalyst is possible by Ar flushing. We, therefore, suggest that the build-up of OHgroups deactivate the In13/CeO2 catalyst and some of these OH groups could be removed during flushing with inert gas, causing a partial regeneration. However, the decreased surface area is not reversible, and this results in a continuous decrease in the activity of the catalyst after repeated experiments, even if the catalyst is flushed with Ar between the experiments.

CO2 methanation over the Ni-based catalysts supported on nano-CeO2 with varied morphologies

A series of CeO2 supports with particular morphologies (nanorods, nanocubes, nanooctas, and nanoparticles) were successfully fabricated by controlling the parameters of the hydrothermal method. The obtained nano-CeO2 materials were utilized as the supports of the Ni-based CO2 methanation catalysts prepared by the incipient impregnation method. It was found that the catalyst supported on the CeO2 nanoparticles (5Ni/NPs) exhibited much higher catalytic activity and better stability than those of catalysts with other morphological CeO2 supports. Thus, the catalytic performance of Ni/CeO2 catalysts could be facilely tuned and optimized by precisely designing the morphology of the CeO2 support. The XPS, CO2-TPD, and H2-TPR characterizing techniques showed that Ni-based catalysts supported on nano-CeO2 with varied morphologies displayed different catalytic performances. It was supposed that the typical merits, such as the abundant oxygen vacancy, medium basic sites, moderate metal-support interaction, excellent reduction ability, etc., were considered as the main origins for the enhancement of the low-temperature catalytic activities. Furthermore, the kinetic study revealed that the Ni-based catalysts supported on the nano-CeO2 with varied morphologies performed the different apparent activation energies toward CO2 methanation. The specific reaction intermediates and possible reaction pathways were carefully investigated through the in-situ DRIFTS and online TPSR techniques. Overall, this work would provide new perspectives that the roles of the morphology effect of the support ought to be emphatically considered when designing new catalysts.

Efficient ammonia synthesis over Ru/CeO2-PrOx catalysts with controlled Ru dispersion by Ru-Pr interaction

Ru/CeO2-PrOx catalysts for NH3 synthesis were prepared using the urea-based homogeneous co-precipitation method, and the effect of Pr-doped CeO2 support on the catalytic activity was investigated. An optimal range of Pr content (25–75 %) improved NH3 synthesis activity. CO pulse adsorption and operando X-ray absorption fine structure (XAFS) measurements revealed that the increase in NH3 synthesis activity was due to the improvement in Ru dispersion by the interaction between PrOx and Ru, rather than the generally discussed Ce3+/Ce4+ ratio. However, excess Pr doping prevented the Ru reduction and formation of active sites. In this Ru/CeO2-PrOx catalyst system, the activity is governed by the number of active sites that can be controlled by the Pr content. In the high-pressure evaluation (5 MPaG), the NH3 synthesis rate of the Ru/CeO2-PrOx catalyst (Ce/Pr = 1) was 9.0 mmol g-1h−1, which is 1.4 times higher than that of the Ru/CeO2 catalyst.

Selective Catalytic Reduction of NOx with NH3 over Mn2O3 Supported with Different Morphology of CeO2 Catalysts

AbstractThree different morphologies of CeO2 supports (nanoparticle, nanocube, and nanorod) were prepared by hydrothermal technique and further Mn2O3 metal was impregnated on CeO2 supports using wet‐impregnation methods, and their activity for NO reduction using NH3−SCR technique was analysed. The synthesized catalysts and supports were further characterized through scanning electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), X‐ray Photoelectron Spectroscopy (XPS), and transmission electron microscopy (TEM), and Brunauer‐Emmett‐Teller (BET). The catalytic performance of Mn2O3/CeO2‐nanoparticle has shown the highest conversion (76 %) compared to the other two catalysts in the temperature range of 50–450 °C.

Redox dynamics of platinum species on CeO2 during CO oxidation reaction

Ceria supported platinum catalysts play an important role in exhaust emission catalysis. Because of the interactions between catalyst and reactants under complex reaction conditions, Pt species may exhibit dynamic structural changes as a function of the reactant pressure and reaction temperature, making it difficult to determine the structure-performance relationship. In this study, the chemical states and dynamics of several typical Pt species, including PtOx, Pt–O–Ce and reduced Pt nanoparticles (NPs), in CO oxidation reaction and their correlations with activity were explored. It was found that Pt–O–Ce species with strong Pt–O bonds remained in the ionic state during the light off reaction, while PtOx species that interacted weakly with CeO2 could be easily reduced to metallic Pt (Pt0), which also exhibited better activity due to the enhanced reducibility of the Pt NPs-CeO2 interface. Although the initial activity of the Pt/CeO2 catalyst can be improved through reduction with H2, the metallic Pt NPs, especially derived from the reduction of Pt–O–Ce dominated catalysts, can get reoxidized to the less active Ptn+–O–Ce (n = 2–δ) species during the reaction. A detailed in situ characterization revealed that the oxidation of metallic Pt NPs arises from oxygen reverse spillover from the CeO2 support. This study shows that understanding the reaction-driven structural dynamics of Pt species is essential for exploring the reaction mechanism and elucidating how the catalyst is activated and deactivated in the reaction.

Introduction of ZnO, Sn, and P promoters in CuO/CeO2 catalysts for improved production of dimethyldichlorosilane in the Rochow-Müller reaction

Developing an efficiently supported Cu-based catalyst with promoters to substitute the existing non-supported Cu-based catalysts is highly desirable to the Rochow-Müller reaction. Using a simple ball-milling method and CeO2 support, we prepared a high-performance CuO-ZnO-P-Sn/CeO2 catalyst by integrating highly dispersed multicomponent promoters of ZnO, Sn, and P with the active component CuO. This catalyst shows a significantly enhanced dimethyldichlorosilane selectivity because these promoters can substantially increase the Cu+ content and the formation of an active CuxSi phase. This work provides a new approach to efficiently designing Cu-based catalysts for the Rochow-Müller reaction.

Facile synthesis of multi-layered nanostructured Ni/CeO2 catalyst plus in-situ pre-treatment for efficient dry reforming of methane

A multi-layered nanostructured Ni/CeO2 catalyst was synthesized through a facile one-pot hydrothermal reaction. The influence of catalyst pre-treatment was investigated as an efficient and easy strategy to improve its catalytic activity. The catalyst exhibited stable above 90% CO2 and 85% CH4 reactant conversions and high product H2/CO ratio (close to 0.95) for DRM at 700 °C for 24 h, with a two-step pre-treatment of the catalyst (H2 reduction followed by CO2 oxidation). This can be ascribed to the multi-layered structure of CeO2 support, enhancing of exposed metal-support interface between Ni and the CeO2 and formation of carbon and oxygen species on the catalyst surface, as indicated by characterizations of H2-TPR, XPS, XRD, FTIR and HAADF-STEM. The simple synthesis and pre-treatment method of such Ni/CeO2 catalyst with high DRM performance offers new opportunities for CeO2 application into DRM reaction as a promising support material.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

Evolution of Pd chemical states and effects of C3H6 and H2O on the CO oxidation over Pd/CeO2 catalyst

Determination of dynamic changes of the supported Pd catalysts under the reaction conditions of CO/Hydrocarbons (HCs) oxidation is of great importance to the development of high performance catalysts for vehicle exhaust purification. Here we found that Pd/CeO2 catalysts dominated with either PdO or Ce1−xPdxO2−δ species, obtained by modulating the interaction between the Pd precursors and the CeO2 support during the preparation, show different dynamic properties under the conditions of CO oxidation and also different deactivation behaviors when C3H6 is coexisting. Under the CO oxidation condition, the PdO species can be easily reduced to metallic Pd, whereas the Ce1−xPdxO2−δ species remain mainly as ionic Pd2+. In situ IR characterization revealed that the chemical states of Pd species on CeO2 during CO oxidation were related to their redox properties, which also dramatically affect the role of C3H6 and H2O in the reactions.