Catalytic Performance Of Co Research Articles

Enhancing the catalytic performance of Co substituted NiAl2O4 spinel by ultrasonic spray pyrolysis method for steam and dry reforming of methane

(Ni,Co)Al2O4 mesoporous spinel particles with a high specific surface area were synthesized in a single-step by ultrasonic spray pyrolysis at 1000 °C. After reduction, a uniform metal distribution was obtained on the support, which was used as a catalyst for dry and steam reforming of methane. Substituting Ni with Co resulted in a substantial increase in the specific surface area from 118 m2/g to 182 m2/g as a result of different decomposition paths that occurs for Ni and Co salts in the pyrolysis reactions. Results show that partial substitution of Ni with Co, between 20 and 50%, significantly increased the methane conversion values and improved the stability of the catalysts in the time on stream experiments. It also shows that partial substitution substantially improved the catalyst resistance against carbon deposition in the dry reforming process. The complete replacement of the cobalt with nickel in spinel structure caused a significant drop in catalytic properties.

CeO2 nanoparticles modified by CuO nanoparticles for low-temperature CO oxidation with high catalytic activity

CeO2 nanocomposites modified by CuO are successfully synthesized by a facile hydrothermal method. The influence of different Cu contents on the crystal structure, morphology, surface element valence, specific surface area, and material reduction temperature has been characterized by many different technical characterization means of XRD, SEM, TEM, Raman, XPS, specific surface area measurement and temperature programmed control under hydrogen, respectively. With the increasing of Cu metal content, the grain size tends to decrease and specific surface area of the sample tends to increase. The CO catalytic oxidation performance of CuO–CeO2 nanocomposites is studied by gas chromatography. Compared with pure CeO2, the CuO–CeO2 nanocomposite catalysts showed more active catalytic performance. The temperature with catalyst rate of 50% in all CuO–CeO2 nanocomposite catalysts for CO conversion is relatively low (77 < T50 < 172 °C). In all as-prepared nanocatalysts, the CuO–CeO2 nanocomposite catalyst with 30 wt% Cu plays the best catalytic activity and the temperature of 50% CO conversion could be down to 77 °C. The introduction of transition metal element Cu could facilitate the interaction of the material surface, promoting the generation of oxygen vacancy, so as to improve the conversion efficiency of CuO modified CeO2 nanocomposite for CO catalytic oxidation at low temperature.

Lithium incorporation assisted synthesis of ultra-small Mo2C nanodots as efficient photocatalytic H2 evolution cocatalysts

Photocatalytic H2 production is a promising way utilizing solar energy to replace fossil fuels. To develop highly efficient, earth-abundant, and low-cost cocatalysts to replace Pt is significant for the scalable solar H2 production. Herein, a lithium incorporation assisted method is developed to synthesize ultra-small Mo2C nanodots, whose cocatalytic activity is 12.23 times of the pristine MoC coupled with CdS. Morevoer, the photocatalytic performance of Mo2C/CdS measured in the lactic acid aqueous solution is 5.81 times of Pt/CdS under the same condition and 71% of Pt/CdS measured in the Na2S/Na2SO3 solution. The apparent quantum yield (AQY) at 420 nm is as high as 39%. And it shows a better cocatalytic performance than Pt loaded on g-C3N4. The high cocatalytic performance is attributed to the more exposed active surface area because of the small size and high loading amounts of Mo2C on carbon. The mechanism study suggests that the Li ion incorporation is beneficial for the formation of ultra-small MoO2 nanodots intermediate during the pyrolysis of ammonium molybdate and ultra-small MoO2 nanodots are transformed to ultra-small Mo2C nanodots accompanying with the Li ion removal after the further carbonization. It is expected that this strategy can be applied to synthesize other ultra-small metal compound nanodots.

Fabrication of Co3O4 nanospheres and their catalytic performances for toluene oxidation: The distinct effects of morphology and oxygen species

Co3O4 shows great effective and active on account of its weaker Co–O bond and higher oxygen binding rate. Co3O4 catalysts with different morphologies exhibit great difference in catalytic activity, which is closely related to their surface element composition, oxygen species and predominantly exposed crystal facets. Morphology and facet control have been proved to be effective routes to vary catalytic performances of Co based catalysts. In this work, three self-assembled Co3O4 nanospheres with different morphologies were successfully prepared by solvothermal and hydrothermal methods with different cobalt precursors without using any template, and were employed to the complete catalytical combustion of toluene. The best catalyst, H sample achieved a toluene conversion of 90 % at approximately 248 °C, which was 50 °C lower than that of the P sample. The superior catalytic performance of the H sample could be attributed to its higher Co3+ content, more adsorbed oxygen species and highly active {110} facets. More importantly, the H sample showed a stable activity for toluene catalytic combustion during 100 h test and displayed a good water resistance property, showing a great potential for practical applications.

Synthesis of Highly Efficient CuCeZr Catalyst Derived from UiO-66 Precursor for CO Oxidation

CuCeZr samples derived from UiO-66 precursor were achieved. The effect of treatment temperature (500–800 °C) and prepared methods (impregnation method and one pot method) on the structure and CO catalytic performance of CuCeZr samples was investigated. The samples were measured by N2 sorption isotherms, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and H2-temperature program reduction (H2-TPR). It was found that calcination temperature and prepared way intensely influenced physicochemical parameters, oxygen vacancy and low-temperature reduction ability of CuCeZr catalysts. CuCeZr catalyst prepared by impregnation method at 700 °C (CuCeZr700-i) exhibited highest catalytic performance for CO oxidation (T100 = 140 °C). High dispersed easily reducible surface species, low valence Cu species, surface lattice oxygen and oxygen vacancy were thought to improve catalytic performance. In addition, CuCeZr700-i presented a good cycle performance, water resistance, and poor stability. The structure of catalyst after reaction was characterized. It was found that the long reaction time led to the decrease of low-temperature easily reducible surface copper species, thereby resulting in slight decrease of reaction stability.

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N-doped Carbon Catalysts.

Ni,N-doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2 R) to CO; this activity has often been attributed to the presence of nitrogen-coordinated, single Ni atom active sites. However, experimentally confirming Ni-N bonding and correlating CO2 reduction (CO2 R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni,N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2 R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal-porphyrin catalysts.

Characteristic and Catalytic Performance of Co and Co-Mo Metal Impregnated in Sarulla Natural Zeolite Catalyst for Hydrocracking of MEFA Rubber Seed Oil into Biogasoline Fraction

This research was aimed to investigate the effect of Co and Co-Mo metal loaded on Sarulla Natural Zeolite which has been activated and calcined (SNZ-Cal) as supports for better understanding of characterization and catalytic activity on hydrocracking of MEFA rubber seed oil. The Co and Co-Mo metal was added through a wet impregnation method using Co(NO3)2·6H2O and (NH4)·6Mo7O24·4H2O precursor salts. The catalyst was oxidized at 500 °C for 2 h within oxygen gas flow, followed by a reduction process with H2 gas flow with similar condition to obtain the catalysts. Based on the result, it was found that the resulted catalysts displayed an increase in crystal grain size compared to the metal-free catalyst. Particularly, catalyst that was impregnated with Co metal has a larger surface area and pore diameter and smaller pore volume than Co-Mo metal impregnated to the catalyst. In fact, it was revealed that this catalyst possessed the highest catalytic activity and selectivity. Furthermore, the resulting gas products reached 64 wt.% and the distribution of biogasoline fraction of hydrocarbons (C6-C12) amounted to 83.19 wt.%.

Size‐controlled Synthesis of Hematite α‐Fe2O3Nanodisks Closed with (0001) Basal Facets and {11‐20} Side Facets and their Catalytic Performance for CO2Hydrogenation

AbstractAn improved hematite α‐Fe2O3catalysts composed of uniform nanodisks closed with (0001) basal facets and {11‐20} side facets are prepared via a simple hydrothermal route. Moreover, by simply tuning the mass of the reaction precursors of Fe(NO3)3⋅9H2O, the size of the obtained hematite α‐Fe2O3nanodisks is controlled in the range of 600–100 nm in diameter and 43–230 nm in thickness, respectively. Due to the exposed (0001) basal facets and {11‐20} facets, in which more amount of Fe3+ion involved, the obtained α‐Fe2O3nanodisks exhibit enhanced reducibility. The maximum H2consumption occurs at relative lower temperature, ca. 490 °C for the smallest α‐Fe2O3nanodisks of 43 nm in thickness and 100 nm in diameter, respectively. Relatively, the Fe3+ions situated at (0001) planes facilitate the Fischer‐Tropsch synthesis (FTS) compared to that situated at {11‐20} planes. Due to the well dispersion and high fraction of (0001) basal facets, the α‐Fe2O3nanodisks with middle size of 190 nm in thickness and 400 nm in diameter propose the high CO2conversion and high hydrocarbon selectivity. Since more amount of (0001) basal facets are masked by the orientation aggregation along [0001] induced by the self‐magnetization, the least α‐Fe2O3nanodisks provide a declined catalytic performance for CO2hydrogenation.

Low-temperature performance controlled by hydroxyl value in polyethylene glycol enveloping Pt-based catalyst for CO/C3H6/NO oxidation

To decrease the diesel vehicle emission, polymer-assisted platinum-based catalysts having an improvement in the dispersion of platinum were developed. This work investigated the structure and redox properties of platinum nanoparticles assisted by polyethylene glycol (PEG) with different hydroxyl value and supported on SiO2-Al2O3 following carbonization and air roasting treatments. Ultraviolet-visible (UV–vis) spectra, in situ FTIR and structural characterization measurements reveal that PEG400-assisted catalyst presents a great interaction with platinum species, affecting the electronic intensity and dispersion of platinum. Reactivity tests show that PEG400-assisted Pt-based catalysts have a better low-temperature catalytic performance in CO, C3H6 and NO oxidation, decreased by around 10−30 °C. It is concluded that the differences in reactivity could be related to the formation and stabilization of platinum species during the preparation.

Performance of ZIF-67 – Derived fold polyhedrons for enhanced photocatalytic hydrogen evolution

Metal-organic framework (MOF) is one of the most promising precursors for the fabrication of advanced photo-semiconductors or cocatalysts due to its diverse structures and unique properties. However, the primitive MOF can not show greater potential and application value. Here Co-ZIF-67 dodecahedron was controllably carved via the different ways for efficiently boosting the photo-catalytic property of hydrogen evolution. This reasonable design can not only preserve polyhedron characteristics with the large specific surface area of ZIF-67, but also improve H2-evolution performance in Eosin Y sensitization system, which depends on the enhanced electronegativity of the surface of ZIF-6 derived polyhedrons and the quite strong adsorption of H and H2O by Co-site. Meanwhile, ligand group or hetero-atom adjacent to metal Co atom owing to the introduction of electronegative heteroatoms overturns the inherent structure and properties of ZIF-67 to a certain extent thereby rearranging the electron distribution and improving transfer efficiency of charge carriers. Additionally, the structural evolution of ZIF-67 constructs an efficient transport channels for migration of electron, which eliminates the resistance to be overcome when electrons migrate from the inside of a semiconductor to the surface. And the increase of optical absorption density caused by hyperchromicity effect is also a factor that can not be ignored for evolving the co-catalytic performance of ZIF-67.

Investigation of the Influence of Process Conditions on the Catalytic Performance of Co–Ce/SiO2 Catalyst for CO Hydrogenation Reaction using RSM Method

AbstractThe Co−Ce/SiO2 catalyst was prepared using fusion method and evaluated in the fixed bed micro‐reactor for light olefins production. The influence of various operational conditions of reaction temperature (300‐450 °C), H2/CO feed ratio (1‐4) and total reaction pressure (1‐10 bar) was investigated on the (C2‐C4) light olefins production using statistical method. The modeling and optimization processes were performed using response surface methodology (RSM) method. A polynomial equation for each response was successfully fitted to the experimental data. The optimization results show that the best operational conditions for light olefins production are as follows: T=365 °C, P=5 bar and H2/CO=2. Under these optimized conditions the selectivity of (C2‐C4) light olefins and CO conversion% are maximum and the methane selectivity is minimum concurrently. Catalyst characterization was performed using, XRD, BET, TGA, DSC, TPR and SEM.

Insights into the precursor effect on the surface structure of γ-Al2O3 and NO + CO catalytic performance of CO-pretreated CuO/MnOx/γ-Al2O3 catalysts

NO reduction by CO was investigated over CO-pretreated CuO/MnOx/γ-Al2O3 catalysts with different metal precursors (nitrate and acetate). It was found that the catalyst prepared from acetate salts (Cu/Mn/Al-A) exhibited significantly higher activity than counterpart catalyst from nitrate precursors (Cu/Mn/Al-N). XRD, XPS and in situ DRIFT were carried out to approach the nature for the different catalytic performance. For both catalysts, copper mainly existed as CuO, but the status of manganese oxide was markedly different. Mn(IV) was predominant in Cu/Mn/Al-N and Mn(III) was enriched in Cu/Mn/Al-A. As a result, different dispersion behaviors of manganese oxide on γ-Al2O3 were displayed, which induced inconsistent Cu-Mn contact. The catalyst obtained from acetate precursor exhibited enriched Cu-Mn contact and thus more Cu+-□-Mn3+/2+ entities would be produced after CO pretreatment, leading to promoted NO dissociation and favorable performance in NO reduction by CO. The present study sheds light on the effective tuning of Cu-O-Mn interfacial sites in CuO/MnOx/γ-Al2O3 via modulating the dispersion behaviors of surface components.

CO and CO₂ Methanation Over Ni/γ-Al₂O₃ Prepared by Deposition-Precipitation Method.

Various Ni catalysts supported on γ-Al₂O₃ were prepared by a wet impregnation (WI) method and deposition-precipitation (DP) method with different precipitants and applied to CO and CO₂ methanation. The prepared catalysts were characterized by various techniques including nitrogen physisorption, X-ray diffraction (XRD), temperature-programmed reduction with H₂ (H₂-TPR), H₂ chemisorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Irrespective of kinds of precipitant, the Ni/γ-Al₂O₃ catalysts prepared with a DP method showed a remarkable enhanced catalytic performance in CO and CO₂ methanation compared with the Ni/γ-Al₂O₃ catalyst prepared with a WI method owing to the higher catalytic active surface area (CASA). In the case of Ni/γ-Al₂O₃ catalysts prepared with a DP method, the high calcination temperatures are not favorable for the high catalytic activity due to the decreased reduction degree of Ni oxide species and CASA. The reduction degree of Ni oxide species can be increased with reduction temperature. However, the higher reduction temperature above 500 °C is not desirable to achieve the high catalytic activity because of the decreased CASA. The selective CO methanation was also accomplished at lower temperatures over the Ni/γ-Al₂O₃ catalyst prepared with a DP method than over the Ni/γ-Al₂O₃ catalyst prepared with a WI method.

Metallic molybdenum sulfide nanodots as platinum-alternative co-catalysts for photocatalytic hydrogen evolution

Molybdenum sulfide (MoS2) has attracted considerable attention as one of noble-metal-free co-catalysts of hydrogen evolution reaction (HER) for artificial photosynthetic water splitting. There are well-known challenges in optimizing its catalytic activity to pursue the replacement of platinum (Pt) for HER, owing to the edge-limited active sites and intrinsically poor conductivity. Herein, we prepared metallic MoS2 nanodots (MNDs) with 1T-phase occupation and edge-exposure maximum to achieve the simultaneous optimization of electric conductivity and active sites. When integrated as co-catalysts with graphitic carbon nitride (g-CN) for sunlight-driven HER in alkaline electrolyte, the outstanding photocatalytic activity with hydrogen evolution rate of 5.62 mmol g−1 h−1, over 280 times higher than that of pure g-CN, demonstrates the excellent co-catalytic performance of 1T-MoS2 NDs (1T-MNDs) that even comparable to state-of-the-art Pt. The photo-induced charge dynamics describe the role of 1T-MNDs in facilitating charge separation as well as surface catalytic reaction, suggesting a promising potential of 1T-MNDs with more active sites and higher conductivity as Pt-alternative co-catalysts for solar hydrogen production.

Sorption-enhanced CO capture over Cu-Mn-Ce composite oxides with LiOH addition: CO oxidation and in-situ CO2 sorption

CuO-MnOx-CeO2 composite catalysts coupled with different amounts of LiOH sorbent were prepared using a solid-state impregnation method and characterized by XRD, N2 adsorption, FE-SEM/EDS and ICP-OES. Then the samples were tested dynamically and isothermally for CO capture involving CO oxidation and CO2 sorption reactions in the temperature range of 30–180 °C under the dry and wet conditions. The results showed that the samples were able to catalytically oxidize CO and chemically absorb CO2 in situ at low temperature. Particularly, CuMnCe/10LiOH exhibited the higher CO oxidation activity than the traditional CuO-MnOx-CeO2 catalyst, and significantly the resistance to water vapor of the sample was also promoted. Isothermal CO2 capture experiment results further revealed that CuMnCe/LiOH could achieve the larger CO2 sorption efficiency by the in-situ way when compared with trapping CO2 diluted in the feed gas. The promoted CO catalytic performance with the excellent tolerance to water poison, and the higher CO2 sorption capacity and efficiency, could be attributed to the synergistic interaction between the CO catalyst and the CO2/H2O sorbent induced by the sorption and transfer of the intermediate gases CO2 and H2O, which modified the influences of two-sidedness CO2 and H2O gases on CO oxidation and CO2 sorption reactions, respectively. These were summarized as a novel concept called Sorption-Enhanced CO Capture (SECC).

Effect of PdOx structure properties on catalytic performance of Pd/Ce0.67Zr0.33O2 catalyst for CO, HC and NOx elimination

Pd/Ce0.67Zr0.33O2 catalyst was pretreated in different atmosphere respectively, and characterized by CO chemical adsorption, XPS, HR-TEM, H2-TPR, Raman, OSC and in situ DRIFTs to investigate the effect of the structure properties of PdOx species on the catalytic performance for CO, HC and NOx elimination. The results show that Pd/CZ catalyst pretreated in air atmosphere has higher oxidation activity of HC due to having high Pd dispersion and strong interaction between PdOx and CZ support. Pd/CZ-H catalyst pretreated in reducing atmosphere exhibits better catalytic performance of NOx elimination because of having relatively big Pd particle size, more Pd species in metallic state and higher concentration of oxygen vacancies. While for the Pd/CZ-RG catalyst pretreated in reactant atmosphere, strong adsorption of HC species on the surface of catalysts would lead to a part of active sites being covered, which inhibits HC and NO conversions.

Ultrasonic exfoliated ReS2 nanosheets: fabrication and use as co-catalyst for enhancing photocatalytic efficiency of TiO2 nanoparticles under sunlight

Rhenium disulfide (ReS2) is an interesting kind of transition metal dichalcogenide (TMD) because of its thickness-independent and suitable direct-bandgap structure, which could enable highly efficient solar-energy conversion efficiency. Here, we demonstrate an ultrasonic liquid exfoliation technique in combination with grinding to produce high quality ReS2 nanosheets (NSs) on a large scale. After combination with TiO2 nanoparticles, the co-catalytic performance of TiO2@ReS2 nanocomposites is investigated, which presents dramatically enhanced degradation activity of organic pigments under sunlight illumination in comparison with pure TiO2 nanoparticles. The underlying mechanism of enhanced photocatalytic activity can be attributed to improved separation efficiency of photogenerated electron–hole pairs in TiO2@ReS2 nanocomposites, which is confirmed by photoluminescence analysis and photoelectrochemical measurements. Our results demonstrate that the layered ReS2 NS is a promising two-dimensional supporting platform for photocatalysis and moreover it could also provide a new perspective on TMDs co-catalyst.

Catalytic performance of Co and Ni doped Fe-based catalysts for the hydrogenation of CO2 to CO via reverse water-gas shift reaction

Utilization of CO2 by converting it into CO via reverse water-gas shift (rWGS) reaction is of particular interest due to the direct use of CO as feedstock in many significant industrial processes. Here, Co and Ni doped Fe-based catalysts, supported over γ-Al2O3 were prepared by a wet-impregnation method and evaluated for hydrogenation of CO2 to CO at temperatures range of 450–650 °C and atmospheric pressure. The catalytic activity in rWGS reaction mainly depends on the oxide phase of the iron. It was found that introduction of Co- or Ni- in iron oxide catalyst significantly enhanced the activity as compared to the undoped Fe/Al2O3 catalyst. However, among the doped catalysts, Co-Fe/Al2O3 showed highest CO yield (48%) and stable time-on-stream performance for 40 h at 3:1 H2/CO2 feed ratio and space velocity of 1000 mL/gcat.min at 650 °C and atmospheric pressure. The better performance of Co-Fe/Al2O3 catalyst was due to the improved reducibility of iron-oxide after doping of Co- and formation of mixed oxide, which is non-selective for methane formation under the rWGS reaction conditions. The detailed characterization results on surface area, size, morphology, reducibility and thermal stability of the prepared Fe-based catalysts obtained by BET, particle size analysis, SEM, XRD, TPR, and TGA techniques were used to understand the role of dopant in enhancement of the observed catalytic activity.

Enhanced Catalytic Performance for CO2 Hydrogenation to Methanol over N‐doped Graphene Incorporated Cu‐ZnO‐Al2O3 Catalysts

AbstractN‐doped graphene (NG) incorporated Cu‐ZnO‐Al2O3 (CZA) catalysts were prepared by co‐precipitation method and their catalytic performances for CO2 hydrogenation to methanol were evaluated under the reaction conditions of 200 ○C and 3.0 MPa. The results indicate that NG promotes effectively the dispersion of CZA and changes the electron structure of CZA, which could provide synergistic effect for methanol synthesis. When NG content is 10 wt.%, the CO2 conversion and methanol selectivity can achieve the highest values of 8.2% and 84%, respectively, which are much higher than those of traditional CZA catalyst.

Effects of the fabrication strategy on the catalytic performances of Co–Ni bimetal ordered mesoporous catalysts toward CO2 methanation

The interfacial effect between metallic Co and Ni active centers can greatly affect their catalytic performances toward CO2 methanation.