Co3O4 and Mn3O4 Nanoparticles Dispersed on SBA-15: Efficient Catalysts for Methane Combustion

Co₃O₄ and Mn₃O₄ nanoparticles were successfully impregnated on SBA-15 mesoporous silica. A high dispersion of these metal oxide particles was achieved while using a “two-solvents” procedure, allowing a proper control of the metal oxides loading (7 wt%) and size (10–12 nm). These Co₃O₄ and Mn₃O₄ supported oxides on SBA-15 were characterised by means of XRD, BET and TEM techniques. The influence of the nature of the silica support was investigated in terms of porosity and specific surface area. Since, an improved catalytic activity was achieved over SBA-15 mesoporous silica; it appears that its organised porous meso-structure creates a confinement medium which permits a high dispersion of metal oxide nanoparticles. Supported Co₃O₄/SBA-15 (7 wt%) showed the highest catalytic performance in the combustion of methane under lower explosive limit conditions, comparable to perovskites. These materials become therefore novel efficient combustion catalysts at low metal loading.     

Catalytic aerobic oxidation of ethylbenzene over Co/SBA-15

Co(II)O was highly dispersed in the mesopores of SBA-15 by alcoholic impregnation method and characterized by XRD, TEM, UV–VIS DRS, TPR, and XRF techniques. It was found that tetrahedral coordinated Co(II)O was stabilized by SBA-15 at low Co-loading. Co/SBA-15 showed much higher activity than Co(OAc)₂ or Co₃O₄ in the liquid-phase aerobic oxidation of ethylbenzene under solvent-free condition.     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

Bi-Co3O4 catalyzing N2O decomposition with strong resistance to CO2

Bi added to Co₃O₄ by coprecipitation method significantly decreased the average crystalline size of Co₃O₄ and increased the surface area and the active sites of the catalyst in population for catalyzing the N₂O decomposition. Over Bi_0.02Co that was the optimized from the Bi_xCo catalysts, 2000 ppm of N₂O in pure Ar was completely decomposed at 400 °C in GHSV of 20,000 h^− 1. Outstandingly, the catalyst exhibited a strong resistance to CO₂, stable N₂O conversion larger than 95% was obtained over the catalyst in the presence of 10% CO₂ at the reaction temperature.     

Low-temperature CO oxidation by Co3O4 nanocubes on the surface of Co(OH)2 nanosheets

CO oxidation has been performed on Co₃O₄ nanocubes and Co(OH)₂ nanosheets as model catalysts. The reaction rate of CO on Co₃O₄/Co(OH)₂ nanocomposites obtained by one-pot synthesis is about ~ two orders of magnitude higher than that on Co₃O₄ nanomaterials. The catalytic behaviors of different nanomaterials revealed that the assembly with nano building blocks cause the catalytic sites much more active for CO oxidation. The kinetic data showed that the activation energy for CO oxidation over Co₃O₄/Co(OH)₂ nanocomposites was lower than that of other nanomaterials. Since Co(OH)₂ nanosheets can prevent Co₃O₄ nanocubes aggregating, nanocomposites kept good catalytic stability.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Nitrous Oxide Decomposition Over MCO3–Co3O4 (M = Ca, Sr, Ba) Catalysts

In this paper, nitrous oxide decomposition over a series of MCO₃–Co₃O₄ (M = Ca, Sr, Ba) catalysts having M/Co ratios of 0.1–0.4 has been studied. The various catalysts were characterized using thermal (TGA, DTA), XRD, IR and N₂ sorption techniques. N₂O decomposition activity was found to be dependent on the type of the alkaline earth cation, the M/Co ratio, cobalt oxide crystallites sizes, and the calcination temperature.     

A mesoporous oxidation catalyst La–Co–Ce–O prepared by citric acid complexation and organic template decomposition method

The mesoporous catalysts La–Co–Ce–O were successfully prepared in one step by citric acid complexation-organic template decomposition method, which show large surface area (up to 157 m²/g), narrow pore diameter distribution (3.7∼3.9 nm), good thermal stability and high activity for CO and C₃H₈ oxidation. Based on the structural characterization results, it is found that the predominant Co phases are Co₃O₄ crystallites, and the activities of these mesoporous catalysts are not proportional to the amounts of surface cobalt atoms, but mainly related to the physical structure of the catalysts and the effective interaction between cobalt and cerium species. When the surface Co/Ce atomic ratio is close to 1, the catalytic synergy effect between them is maximized.     

Cobalt oxide species supported on SBA-15, KIT-5 and KIT-6 mesoporous silicas for ethyl acetate total oxidation

Cobalt oxide modified SBA-15, KIT-5 and KIT-6 mesoporous silicas with different pore size/pore entrances have been synthesized by a conventional wet impregnation method using cobalt nitrate as the precursor. The modified materials were characterized by N₂-physisorption, XRD, TEM-EDX, XPS, FT-IR, UV–vis and TPR-TG with hydrogen. Their catalytic activities in total oxidation of ethyl acetate were evaluated. A good correlation was observed between the catalytic activity, and the presence of spinel-type Co₃O₄ in the materials. Supports with larger mesopores facilitated the formation of such easily reducible spinel particles. However, the interconnectivity of the mesopores and the uniformity of the channel dimensions also had an influence on the catalytic activity, implying that mass-transfer effects, especially in the case of supports with cage-like mesopores.     

Manganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous oxidation

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co₃O₄, Mn₃O₄ and Mn₂O₃ nanoparticles. The prepared metal oxide nanoparticles of Co₃O₄, Mn₃O₄ and Mn₂O₃ possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co₃O₄ and Mn₃O₄ exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co₃O₄ and Mn₃O₄ nanoparticles illustrated excellent catalytic stability and reusability for nine and four cycles, respectively, toward olefin oxidation.     

Metal (Co,Mn)-amine-functionalized mesoporous silica SBA-15: synthesis,characterization and catalytic properties in hydroxylation of benzene

Mesoporous silica SBA-15 was synthesized using H₃PO₄ and functionalized with ethylendiaminopropyltrimethoxysilane (H₂N–(CH₂)₂–NH–(CH₂)₃–) by grafting method. A variety of transition metals such as Co and Mn have been coordinated with amine-functionalized silica SBA-15. The materials have been characterized by XRD, FT-IR, BET, TGA, ¹³C-NMR, DR UV–Vis, atomic absorption spectroscopy (AAS) and back titration using NaOH (0.1 N). The catalytic performance of obtained catalyst was determined for hydroxylation of benzene using H₂O₂ as oxidant in the presence of O₂ atmosphere. At optimized conditions, the Mn-amine-functionlized mesoporous silica SBA-15 exhibited high catalytic activity at room temperature in the absence of solvent.     

Controllable synthesis of porous Co3O4 nanorods and their ethanol-sensing performance

A simple strategy for synthesizing porous Co₃O₄ nanostructures through a hydrothermal process with subsequent thermal decomposition of the obtained Co(CO3)0·35Cl0·20(OH)1.10 precursors was introduced. To understand the growth mechanism of the Co(CO₃)_0·35Cl_0·20(OH)_1.10 precursors and realize morphology control of the resultant Co₃O₄ nanomaterials, a series of controlled experiments were carried out by varying CO(NH₂)₂ dosages, hydrothermal temperatures and time. The Co₃O₄ nanorods obtained under optimized synthesis conditions demonstrated porous structural features, which were constructed by well-connected nanograins, leaving many pores composed of the space between nanograins. The ethanol-sensing behaviors of these Co₃O₄ nanostructures were evaluated, showing the highest response (19.581) and a short response and recovery time (1 s/10 s) to 100 ppm ethanol. Moreover, the Co₃O₄ sensor demonstrated excellent anti-interference ability toward several interfering gases such as methanol, benzene hexane, and dichloromethane. The stability of the Co₃O₄ sensor was further confirmed by 14 days of continuous testing. Compared with previously reported works, this Co₃O₄ sensor still demonstrated outstanding gas sensing properties due to its unique advantages such as 1D porous nanostructures, high BET surface area, abundant oxygen vacancies, and active cobalt sites.     

Electrochemical surface properties of Co3O4 electrodes

The electrochemical behaviour of Co₃O₄ layers deposited by thermal decomposition of Co(NO₃)₂ at 200–500°C on titanium supports with and without an interlayer of RuO₂ has been studied by cyclic voltammetry, chronopotentiometry and potential step experiments in alkaline solutions. Such variables as the calcination temperature, the solution pH, the potential sweep rate and the oxide loading have been investigated in detail to determine their influence on voltammetric peaks and voltammetric charge. Insight has been gained into the relevance of the latter to surface area determination and to proton diffusion into the oxide layer. The role of the support-active layer interface and especially that of the RuO₂ interlayer has been scrutinized. The importance of surface studies for the understanding of the electrocatalytic behaviour of Co₃O₄ electrodes has been analysed.Presented at the 37th Meeting of the International Society of Electrochemistry, Vilnius, USSR, 25–29 August 1986.     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

Origin of the High Activity and Stability of Co3O4 in Low-temperature CO Oxidation

In this paper, the Co₃O₄ catalysts prepared by the liquid phase precipitation method were investigated with respect to their activity and stability in CO oxidation reaction. The Co₃O₄ catalysts were comparatively investigated by thermal gravimetry analysis (TG-DTG), X-ray powder diffraction (XRD), N₂ adsorption, CO titration and O₂-temperature program desorption (O₂-TPD). The results of XRD show that all the catalysts exist as a pure Co₃O₄ phase with the spinel structure. The high catalytic activity observed at ambient temperature is followed by a gradual decrease. The CO titration experiments show that the Co₃O₄ catalysts possess active oxygen species. The total amount of active oxygen species and the specific surface area decrease with increasing calcination temperature. The O₂-TPD results indicate that O ₂ ^? and O^? are the possible active oxygen species.     

A DFT study of methanol oxidation on Co3O4

By means of spin polarized density functional theory with the GGA + U framework, the reaction mechanism of CH₃OH oxidation on the Co₃O₄ (110)-B and (111)-B surfaces has been investigated. Adsorption situation and a part of reaction cycle for CH₃OH oxidation are clarified. Our results indicated that: i) U value can affect the calculated energetic result significantly; ii) CH₃OH can adsorb with surface lattice oxygen atom (O_2f/O_3f) to form CoO bond directly, and the adsorption of CH₃OH and its decomposition products on (110)-B is more stable than on (111)-B, which means CH₃OH prefers Co^3 + better than Co^2 +; iii) on the (110)-B surface, CH₃OH can form CO₂, H₂O and adsorbed H atom. But on the (111)-B surface, CH₃OH can just form formaldehyde (CH₂O) and adsorbed H atom, this means oxidative capacity of (110)-B (Co^3 +) is higher than (111)-B (Co^2 +). The possible reasons corresponding to the high oxidative of (110)-B come from both Co^3 + and O_2f: Co^3 + tends to bind adsorbed species for further decomposition and O_2f tends to bind more hydrogenation atom involved in methanol due to its low-coordinates number compared to that of O_3f.     

High loading of short WS2 slabs inside SBA-15: promotion with nickel and performance in hydrodesulfurization and hydrogenation

Layered nanoslabs of a WS₂ phase with a well-defined hexagonal crystalline structure, average slab length of 3.6 nm, and stacking number of 3.2 were inserted into the nanotubular channels of SBA-15, an ordered pure silica material (surface area of 800 m²/g, uniform mesopore diameter of 6.5 nm) at loadings up to 60 wt.%. Sonication of a slurry containing SBA-15 in a W(CO)₆–sulfur–diphenylmethane solution yielded an amorphous WS₂ phase inside the mesopores. By sulfidation with 1.5% dimethyldisulfide in toluene under a hydrogen flow at 593 K and 5.4 MPa, the amorphous phase was transformed into hexagonal crystalline WS₂ nanoslabs (as shown by XRD, HRTEM, and selected area electron diffraction (SAED)). The WS₂ nanoslabs were distributed exclusively inside the mesopores in a uniform manner (HRTEM, quantitative microanalysis), without blocking the pores (N₂-sorption), and were oriented with their edge planes toward the support surface. This study constitutes the first report of such a combination of high loading of a well-defined crystalline catalytic phase into the nanotubular channels of mesoporous silica without blocking them. The first well-resolved HRTEM images of the well-defined crystalline catalytic phase (WS₂) inside the SBA-15 nanotubes are presented. A Ni component was introduced into the WS₂/SBA-15 composite by impregnation from an aqueous solution of nickel acetate. It increased the catalytic activity up to a Ni/W ratio of 0.4. In the hydrodesulfurization (HDS) of dibenzothiophene and the hydrogenation (HYD) of toluene, the activity of the optimized NiWS/SBA-15 catalyst was 1.4 and 7.3 times higher, respectively, than that of a sulfided commercial CoMo/Al₂O₃. This finding illustrates the excellent potential of high loading NiWS/SBA-15 catalysts for deep hydrotreatment of petroleum feedstocks.     

Novel aspects of the physical chemistry of Co/SiO2 Fischer–Tropsch catalyst preparations: Cobalt oxide-induced silica migration during calcination of cobalt nitrate-impregnated high surface area silica

Co/SiO₂ catalysts were prepared by aqueous cobalt nitrate impregnations of silicas with different surface areas to study the effect of the support surface area on the reactions occurring during impregnation and calcination and to define the stage and mode of metal–support interactions. TPR analyses of samples calcined in dry air showed the presence of various quantities of cobalt silicate species, while cobalt silicate formation was not discernible by other analytical techniques. Our conclusion, confirmed in our later studies, is that cobalt silicate does not form during impregnation or calcination, but is created during the reduction in the TPR instrument. Because of these and other ambiguities of the TPR analyses, in our continuing studies we preferred alternative analytical approaches.These studies on the calcination stage resulted in the following unusual findings: (1) X-ray photoelectron spectroscopy revealed drastic decreases in the surface cobalt concentration after calcination of high surface silicas impregnated with cobalt nitrate solutions. (2) Infrared spectroscopy indicated much less than expected Co₃O₄ formation upon calcination if high surface area silica was the support. (3) A method was devised to calculate the surface areas of individual components in mixtures. The calculations indicated about 20% surface area losses for the silica in calcined catalysts. (4) Scanning electron micrographs of a calcined catalyst on high surface area silica support showed smaller-sized decorations around the larger silica particles. Energy-dispersive X-ray analysis of the decorations showed Si as major, and Co as a minor component. Pure Co₃O₄ phases were not found by EDX analyses of these decorations. These four seemingly unrelated findings are attributed to a common cause: silica migration and weak bond formation between CoO and SiO₂. The extent of surface area losses (i.e. the extent of silica migration) is about an order of magnitude greater in CoO_x–SiO₂ catalysts than in analogously treated SiO₂. The migration of silica must have occurred in a relatively short time period during the thermal decomposition of cobalt nitrate, while simultaneous migration and oxidation of CoO to Co₃O₄ aggregates also occurred. The CoO species intercepted by SiO₂ were unable to oxidize, resulting in reduced quantity of Co₃O₄ formation. The extensive migration of silica is attributed to strong attraction between SiO₂ and CoO species, inducing the removal of silicic acid or silica molecules from the silica surface.     

Comparison of PdCo/SBA-15 prepared by co-impregnation and sequential impregnation for Fischer–Tropsch synthesis

Properties and catalytic performance of bimetallic Pd–Co/SBA-15 prepared by co-impregnation (0.2Pd–10Co-CIP) and sequential impregnation (0.2Pd–10Co-SIP) for Fischer–Tropsch synthesis (FTS) were investigated. After calcination, Co₃O₄ was formed and located inside the channels of SBA-15 and on external surface. Compared to 0.2Pd–10Co-SIP, 0.2Pd–10Co-CIP had a smaller surface area, pore size, lower reduction temperature and less active sites due to larger particle sizes of Co₃O₄. From FTS testing, 0.2Pd–10Co-SIP provided higher and steadier conversions of CO and H₂ as well as higher yield of C₅–C₉ products.     

The CO methanation over NaY-zeolite supported Ni/Co3O4, Ni/ZrO2, Co3O4/ZrO2 and Ni/Co3O4/ZrO2 catalysts

The CO methanation was studied over zeolite NaY supported Ni, Co₃O₄, ZrO₂ catalysts. The XRD, N₂ physisorption and SEM analysis were used in order to characterize the catalysts. Catalytic activities were carried out under a feed composition of 1% CO, 50% H₂ and 49% He between the 125 °C to 375 °C. Except for the Ni/Co₃O₄/NaY catalyst, all catalysts gave high surface area because of the presence of zeolite NaY. Average pore diameter of the catalysts fell into the mesopore diameter range. The highest CO methanation activity was obtained with Ni/ZrO₂/NaY catalyst at which the CO methanation was started after 175 °C and 100% CO conversion was obtained at 275 °C using the same catalyst.