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The reverse water-gas shift (RWGS) reaction is one of the effective ways of carbon dioxide (CO2) conversion. However, the RWGS catalyst has the problem of poor stability under high temperature. A series of Co/SiO2 catalysts with promoters (CeO2, La2O3, Y2O3 or ZrO2) were prepared by incipient-wetness impregnation method for the RWGS reaction. The catalysts were characterized by X-ray diffractometry, transmission electron microscopy and H2-programmed temperature reduction, etc. The effects of promoters on the catalyst structure and RWGS reaction performance were studied. The results of catalyst characterization show that the particle size of Co3O4 in the catalyst is not significantly changed by adding promoters. The promoters of CeO2, La2O3, Y2O3 and ZrO2 interacte with the cobalt component. The catalytic performance test results show that the CO2 conversion rate of the Co/SiO2 catalysts decreases from 28.3% to 9.0% after reaction at 600 °C for 12 h. The stability of the catalysts with promoters is improved, and the Co-ZrO2/SiO2 catalyst has the best stability, and the CO2 conversion rate is still as high as 21.9% after reaction for 12 h. This is due to the presence of interaction between the promoters and the cobalt component after the addition of the promoters, which improves the stability of the active component of cobalt. [ABSTRACT FROM AUTHOR]

Synthesis of mixed alcohols together with clean fuels from syngas via Fischer-Tropsch synthesis is an attractive route for the utilization of coal, natural gas and biomass. In this work, a monometallic cobalt catalyst (Co/SiO 2 -EOAM) was synthesized by impregnation using ethanolamine modified silica pellet as support and employed for the conversion of syngas. The combustion of carbon and nitrogen species during the calcination of catalyst facilitated the interaction between cobalt and support, which promoted the cobalt dispersion while inhibited the reduction of cobalt oxide. The Co/SiO 2 -EOAM catalyst exhibited much higher activity and selectivity to alcohols compared to un-modified silica supported cobalt catalyst (Co/SiO 2). The higher activity was resulted from the improved cobalt dispersion. The co-existence of abundant metallic cobalt and Co2+ species were responsible for the increasing of alcohols selectivity. • Efficient Co/SiO 2 was developed for mixed alcohols synthesis from syngas. • Higher Co dispersion is obtained by using ethanolamine modified silica as support. • Higher amount of Co0 active sites leads to increased activity. • Co-existence of Co0 and Co2+ is responsible for the alcohols formation. [ABSTRACT FROM AUTHOR]

Comparison of the change of Co 3 O 4 crystallite size with the cobalt loading over SiO 2 supports prepared using different method. • Addition of urea gives smaller Co 3 O 4 crystallite size over SiO 2 support. • The Co 3 O 4 crystallite size over small pore SiO 2 is affected more significantly by addition of urea. • Adding ruthenium salts to the cobalt nitrate solution lowers the Co 3 O 4 crystallite sizes. • The Co/SiO 2 catalyst prepared using OMX showed higher CO conversion and longer stability. In this work, a series of SiO 2 supported Co catalysts have been prepared by adding urea or ruthenium to the cobalt precursor solution compared with the catalysts prepared without using urea. The characterization results show that cobalt is present as Co 3 O 4 over the silica supports. The addition of urea to the catalyst precursor helps to generate smaller crystallite even at very high cobalt loading, while impregnation without using urea results in larger crystallite size as Co loading increases. Likewise, the addition of Ru to the catalyst precursor leads to a more uniform crystallite of Co 3 O 4 , and can help to lower the Co 3 O 4 crystallite size to some extent, which has the similar effect on the catalyst prepared with urea. We have also shown that the support pore size and volume do have significant effect on the crystallite size of the cobalt oxide. The catalytic performances of the Co/SiO 2 catalysts prepared with and without adding urea have been evaluated for Fischer Tropsch synthesis and the catalyst prepared using urea demonstrates significantly improved catalyst activity as well as selectivity to C 5 +. [ABSTRACT FROM AUTHOR]

Unlike Co clusters, isolated Co atoms have been shown to be selective for catalytic dehydrogenation of ethane to ethylene; however, preparation of isolated Co sites requires special preparation procedures. Here, we demonstrate that Atomic Layer Deposition (ALD) of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(III) (Co(TMHD)3) on silica and other supports is effective in producing these isolated species. Silica-supported catalysts prepared with one ALD cycle showed ethylene selectivities greater than 96% at 923 K and were stable when CO2 was co-fed with the ethane. Co catalysts prepared by impregnation formed clusters that were significantly less active, selective, and stable. Rates and selectivities also decreased for catalysts with multiple ALD cycles. Isolated Co catalysts prepared on Al2O3 and MgAl2O4 showed reasonable selectivity for ethane dehydrogenation but were not as effective as their silica counterpart.

Highlights: [•] A novel citric acid assisted synthesis method is proposed to prepare highly dispersed metallic Co/SiO2 catalysts directly. [•] The whole catalysts preparation process is easily operated with inexpensive materials. [•] The activity of as-prepared Co/SiO2 catalysts is much higher and about fourfold of that prepared by conventional methods. [Copyright &y& Elsevier]

Highlights: [•] Application of ToF-SIMS to the characterization of cobalt catalysts for FT synthesis. [•] Direct confirmation of cobalt silicate formation on the Co/SiO2 surface. [•] New ToF-SIMS procedure allowed to determine an exact composition of Co catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] Trace CO increases C3+ selectivity during the C2H4 +H2 reaction over Co/SiO2. [•] The predominant primary products are ethane and cis-2-butene. [•] C4 isomerisation and other secondary reactions are prominent at high conversion. [•] CO inhibits very strongly, by more than two orders of magnitude at 60̊C. [•] The catalyst deactivates with and without CO but the C3+ selectivity is unchanged. [ABSTRACT FROM AUTHOR]

The dry reforming of methane is carried out on Co/SiO2 modified catalysts. The catalytic activity and stability of the prepared catalysts are closely depending on MgO, SrO or BaO additives. Thus, it was shown that the addition of these oxides to the Co/SiO2 reference sample revealed a very positive effect on the resistance to carbon deposition and contributed therefore the observed catalytic stability by gasification of surface carbon species. [ABSTRACT FROM AUTHOR]

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Abstract: A series of supported Co/SiO2 catalysts were prepared by surface impregnation combustion method using cobalt nitrates and citric acid, and the precursors were burnt in different atmospheres. The effects of different calcination atmospheres on the properties of the supported Co/SiO2 catalysts were systemically studied by TG-DTA, XRD, Raman spectrum, TPR, in situ FTIR, TEM, BET and H2-chemisorption techniques. The burnt catalyst Cargon-air-reduction which was first burnt in argon and then oxidized in air had about 10nm Co3O4 crystalline size, much smaller than that which was directly burnt in air (Co3O4 size: about 15nm) and that prepared by conventional impregnation method (Co3O4 size: about 32nm) using cobalt nitrate as impregnating solution. Characterizations and FTS results of two other references using different organic cobalt salt aqueous (cobalt acetate and cobalt citrate) as impregnating solution were also added in the supporting information. Comparing with our previously reported Cargon catalyst directly burnt in the argon atmosphere without further reduction, the influence from surface amorphous carbon and carbonic residues was completely eliminated. The activity of the burnt catalyst Cargon-air-reduction prepared by surface impregnation method was threefold higher than that of the reference CN-reduction prepared by conventional incipient-wetness impregnation method. The surface impregnation combustion method described herein was promising to prepare highly dispersed supported metallic catalysts with smaller particle sizes. [Copyright &y& Elsevier]

Abstract: Co/SiO2 catalysts with higher dispersion of Co0 as well as high reducibility of Co were prepared by impregnation using an aqueous solution containing Co nitrate and a glycol under different glycol/Co2+ molar ratios. Glycols with different structures, i.e., straight chain and branched ones, were used for preparation of the catalysts to help understand the fundamental role of the glycols. The CO conversion was enhanced in the presence of these glycols. The highest conversion was around 60% under 503K and 1.1MPa regardless of the structures of the glycols, whereas the optimum glycol/Co2+ molar ratio for the highest conversion shifted toward higher values with decreasing molecular weight of the glycols. On the other hand, these conversions fell on one curve irrespective of the structures of the glycols when plotted against the C/Co2+ atomic ratios of the impregnation solutions, indicating that the C/Co2+ ratio was one of crucial factors for activity enhancement induced by the glycols. Furthermore, XRD and Co K-edge EXAFS measurements revealed that Co3O4 species with smaller sizes was formed after calcination in the presence of the glycols. Size of Co3O4 species fell on one curve when plotted against the C/Co2+ atomic ratios, which was consistent well with activity data. FT-IR measurements also provided evidence that Co species interacted with triethylene glycol (TEG) derivatives during calcination in the range of 400–470K. In analogy to the polymerizable complex method, it was considered that this interaction included polymer complex-like species, in which Co species was immobilized in network of cross-linked structures formed by ester polymerization of TEG and dicarboxylic acid derived from TEG, resulting in the formation of smaller Co3O4 species after calcination, and the smaller Co0 nanoparticles after H2 reduction, i.e., enhanced FTS activity. [Copyright &y& Elsevier]

Abstract: Vapor-phase hydrogenolysis of ethyl lactate to 1,2-propanediol was performed over a series of SiO2 supported metal (Fe, Co, Ni, Ru, and Pd) catalysts in a fixed-bed reactor. Among them, the Co/SiO2 and Cu/SiO2 catalysts exhibit promising performance, and the Co/SiO2 were more active than the traditional copper catalysts under mild conditions. Effects of support, metal loading and preparation method were investigated to optimize the performance of the Co-based catalysts. Over the optimal catalyst (a 10wt.% Co/SiO2 catalyst prepared via rotary evaporation drying method), the 1,2-propanediol selectivity was in excess of 98% at 90.2% lactate conversion, 2.5MPa and 160°C. The cobalt catalysts were characterized by X-ray diffraction (XRD) and temperature programmed reduction by H2 (H2-TPR) and temperature programmed desorption of H2 (H2-TPD). Interestingly, a quasi-linear correlation is observed between the average reaction rate and the percentage of bulk-like Co3O4 phase precursors, suggesting that the metallic cobalt from the bulk-like Co3O4 phase precursor is more active than that from the cobalt surface support species. The emerging technologies for production of low-cost lactate ester, make this high-yield route a sustainable benign process for 1,2-propanediol. [Copyright &y& Elsevier]

Abstract: Catalytic wall (structured) reactors and structured supports are suitable to study the catalytic properties of nanosized materials. The coating of metallic (aluminum and stainless steel) plates by thin layers of active phase is presented in two cases, VO x /TiO2 and Co/SiO2, catalysts used in the oxidative dehydrogenation (ODH) of propane and in Fischer–Tropsch synthesis (FTS) of clean fuels, respectively. The preparation of coated plates and their characterisation by various methods of physicochemical analysis are described. Both chemical and physical methods were used for coating. VO x /TiO2 layers were obtained by grafting of Ti (on Al or stainless-steel plates) and V (on TiO2) alkoxides and use of sol–gel media or suspension. A silica primer was deposited (on stainless-steel plate) by plasma-assisted chemical vapour deposition (PACVD) onto which Co oxide and silica were coprecipitated from sol–gel. The catalytic experiments in the respective reactions were carried out in special plate reactors and compared with those of catalytic powders. The study shows that the coating of a metallic substrate by a catalyst is not straightforward and requires specific studies dealing with both chemistry (chemical affinity between substrate and catalytic layers) and catalytic engineering (catalytic performance in taylor-made reactors). [Copyright &y& Elsevier]

Abstract: Application of the simple, rational catalyst synthesis method of strong electrostatic adsorption was applied to hexaammine cobalt(III) chloride (CoHA) complexes over silica and carbon, which potentially affects the preparation of Fisher–Tropsch and other catalysts. Uptake versus pH was studied, and resulting materials were characterized by powder XRD, EXAFS, XANES, and STEM at each stage of the preparation procedure. Large differences occurred when CoHA was contacted at high pH over silica and carbon surfaces with similar points of zero charge. The Co ammine–silica interaction could be described by a purely electrostatic interaction, was very strong, and prevented reduction up to the high temperatures at which significant Co sintering occurred. However, sufficient interaction existed so that the normally lower-temperature stable hexagonal close-packing phase was retained by the metal crystallites on silica. Over carbon, CoHA underwent a reductive deammination on contact with the carbon to form large crystals of Co3O4. While this precursor phase reduces at much lower temperature than the silica-supported Co ammines, the large initial size of the Co3O4 phase also prevented the formation of small Co particles. Our findings demonstrate that high Co metal dispersion on carbon might be achieved with synthesis parameters (i.e., other Co complexes, carbons, or impregnation conditions) that yield a highly dispersed Co precursor. [Copyright &y& Elsevier]

Abstract: The steam reforming of ethanol was studied at on a single catalytic bed reactor containing alone or mixed with and on a double bed system formed by and separate layers. Catalysts were characterized by X-ray diffraction, atomic absorption spectrometry, Raman spectroscopy, and temperature programmed reduction with hydrogen. After calcination at the catalyst presents as the main phase containing cobalt. The reduction of to metallic Co and of to occurs at temperature near to . All catalytic systems had shown average conversion of 90% for the steam reforming of ethanol at . Hydrogen is the main constituent of the reaction effluent, which also contains CO, , and . The amounts of methane and CO produced with the double bed reactor were lower than that on pure . Higher decrease of the CO content is observed for the single bed reactor with the and mixture. In this case, the decrease of CO content was about 80% compared to pure . [Copyright &y& Elsevier]

The effect of addition of Pd/b on the Co/SiO catalyst was studied for F-T reaction. Pd/b could enhance the formation of C-C isoparaffins while the Co/SiO catalyst alone gave the products with wide carbon numbers distribution. The reason is the olefins and long-chain normal paraffins from F-T reaction on Co/SiO catalyst form light hydrocarbons containing isoparaffins through the hydrocracking and hydroisomerization on Pd/b. For Co/SiO+Pd/b catalyst, the selectivity to isoparaffins depends on the contact conditions. The granular hybrid catalyst is much more selective for isomerization than the powder hybrid catalyst, while the selectivity to CH, n-paraffins and olefins is lower than that on the powder hybrid catalyst. [ABSTRACT FROM AUTHOR]

Reducibility is a key factor when controlling the Fischer-Tropsch (F-T) activity of a cobalt catalyst. We have demonstrated on a cobalt-silica system that by conducting a relatively simple pretreatment step on the SiO 2 support with ammonium nitrate can significantly improve reducibility of the catalyst, and thus enhancing the F-T activity which is comparable to more commonly performed, and more costly methods involving noble metal-modification to promote reduction of cobalt. Through catalyst preparation, the Co particle size effect on F-T performance was excluded, and an increase of more than three times higher initial TOF (turnover frequency) for CO conversion is disclosed. Moreover, NH 4 NO 3 acts as a "cleaner", allowing the activated sites to be available for CO 2 formation. Unlabelled Image • Reducibility of cobalt is remarkably improved by modifying silica support with NH 4 NO 3. • Co particle size effect is excluded. • Much higher activity of NH 4 NO 3 -modified Co/SiO 2 than unmodified catalyst. • CO 2 selectivity is decreased on NH 4 NO 3 -modified Co/SiO 2. [ABSTRACT FROM AUTHOR]

Unlike Co clusters, isolated Co atoms have been shown to be selective for catalytic dehydrogenation of ethane to ethylene; however, preparation of isolated Co sites requires special preparation procedures. Here, we demonstrate that Atomic Layer Deposition (ALD) of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(III) (Co(TMHD)3) on silica and other supports is effective in producing these isolated species. Silica-supported catalysts prepared with one ALD cycle showed ethylene selectivities greater than 96% at 923 K and were stable when CO2 was co-fed with the ethane. Co catalysts prepared by impregnation formed clusters that were significantly less active, selective, and stable. Rates and selectivities also decreased for catalysts with multiple ALD cycles. Isolated Co catalysts prepared on Al2O3 and MgAl2O4 showed reasonable selectivity for ethane dehydrogenation but were not as effective as their silica counterpart. [ABSTRACT FROM AUTHOR]