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Abstract: The study focused on synthesis of cobalt on cobalt-aluminate catalyst in one-pot via the solvothermal process. The obtained catalysts apparently exhibited higher activities than that prepared from the conventional solvothermal-derived alumina-supported cobalt catalyst without any changes in product selectivity during methanation. Enhanced activities can be attributed to the smaller amount of non-reducible cobalt-aluminate formed (at temperature <800°C. Increased Co/Al molar ratios (1.0 and 2.0) also resulted in increased activities whereas the holding time during solvothermal synthesis had only little effect. [Copyright &y& Elsevier]

Abstract: This paper investigates the isosynthesis via CO hydrogenation over zirconia and ceria catalysts. Various techniques including XRD, NH3-TPD, CO2-TPD and BET surface area were employed for the catalyst characterization. The results showed that not only acid–base properties, but also crystallite size and crystal phase essentially influenced the catalytic performance. It was found that the activity and the selectivity of isobutene in hydrocarbons on nanoscale catalysts were higher than those on the micronscale ones. Moreover, the acid–base properties were dependent on the fraction of tetragonal phase for zirconia, but independent on crystal phase for ceria. The synthesized nanoscale zirconias were more active than the commercial one but less than the nanoscale ceria. From the results, it was indicated that zirconia with 29% tetragonal phase exhibited the highest activity. Furthermore, the presence of tetragonal phase in zirconia played an important role on the selectivity of isobutene in hydrocarbons. [Copyright &y& Elsevier]

Abstract: In the present study, the catalytic behaviors of mixed TiO2-SiO2-supported cobalt (Co) Fischer–Tropsch (FT) catalysts via carbon monoxide (CO) hydrogenation were investigated. The various weight ratios of TiO2/SiO2 were prepared, then consequently impregnated with the cobalt precursor. After calcination, the various samples were characterized using XRD, Raman spectroscopy, scanning electron microscopy/energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and H2 chemisorption. The characteristics of various samples were further discussed in more details. Based on the reaction study, it revealed that the presence of titania in the mixed supports resulted in decreased activities dramatically. However, longer chain hydrocarbons such as C2–C5 can be obtained substantially with increasing the amounts of titania in the mixed supports. [Copyright &y& Elsevier]

The TiO2 supports consisting of different phases were modified with ZrO2 for TiO2-supported Co catalysts. It showed that modification on the pure anatase TiO2 resulted in decreased activities, but increased chain growth probability. In contrary, the modification on mixed phase TiO2 resulted in increased activities without effects on selectivity. [ABSTRACT FROM AUTHOR]

Abstract: The present research showed dependence of crystalline phases in titania on the catalytic properties of Co/TiO2 catalysts during CO hydrogenation. A comparative study of anatase TiO2- and rultile-anatase coupled TiO2-supported Co catalysts was conducted. It was found that the presence of rutile phase (19mol%) in titania resulted in a significant increase in the catalytic activity during CO hydrogenation. It was proposed that the role of rutile phase was to increase the stability of the support. The impact of water vapor produced during reduction on the formation of cobalt species strongly interacted with the support was probably inhibited by the presence of rutile phase in titania leading to a decrease in the reducibility loss during reduction. [Copyright &y& Elsevier]

Zr promotion has been shown to improve the activity of Co/SiO2 and Co/Al2O3 Fischer–Tropsch synthesis (FTS) catalysts. However, little is known about how it works. The focus of this study was to investigate the impact of Zr modification of alumina used to support Co catalysts. Zr was first impregnated into alumina to produce Zr-modified alumina supports containing 2–11 wt% of ZrO2 in the final catalyst. Co catalysts having 20 wt% Co were then prepared from these supports by incipient wetness. It was found that Zr modification had a significant impact on the catalyst properties: FTS rate per gram of catalyst increased significantly (>65% at steady state) with Zr modification and Co reducibility, especially during standard reduction, also increased. H2 chemisorption, however, was found to be essentially constant with Zr modification. The impact of Zr modification is likely due to stabilization of the alumina support, prevention or blockage of Co surface “aluminate” formation, and an increase in Co reducibility to the active catalytic metallic phase. SSITKA results for CO hydrogenation showed an increase in the number of active surface intermediates (NM) with Zr modification while the intrinsic activity (1/τM) remained constant, confirming that the major impact of Zr was in increasing the concentration of active Co surface sites. Because of the inconsistency of the turnover frequency calculated based on H2 chemisorption with the 1/τM results, it is suggested that the standard adsorption conditions usually used for Co may not be adequate for modified Co catalysts such as the ones studied here. [Copyright &y& Elsevier]

The effect of the addition of CO during H2 reduction on Co-support compound formation in a Co/γ-Al2O3 catalyst was investigated. It is known that such compound formation can occur during catalyst reduction, is facilitated by the presence of water vapor, and results in a less active catalyst. In this study, a H2 flow containing CO (1–9 vol.%) was used for standard reduction. Water vapor was also added (3 vol.%) in one series of experiments in order to examine the impact of CO when relatively high partial pressures of water vapor are also present. After reduction at various conditions, the pretreated catalyst samples were characterized and CO hydrogenation (H2/CO=10/1, 220 °C, 1.8 atm) also performed. Both initial and steady-state rates during CO hydrogenation went through a maximum for the addition of 3–5 vol.% CO during standard reduction. The maximum rate was about four times that in the case where no CO was added. A similar trend was found even where reduction occurred with a high partial pressure of water vapor. It is concluded that the addition of CO during reduction has a significant effect on activity of the catalyst due to increases in both Co reducibility and dispersion. [Copyright &y& Elsevier]

Abstract: The effect of catalyst calcination temperature (450°C, 600°C, and 750°C) on catalytic performance of synthesized and commercial grade sulfated zirconia catalysts towards isosynthesis was studied. The characteristics of these catalysts were determined by using various techniques including BET surface area, XRD, NH3- and CO2-TPD, ESR, and XPS in order to relate the catalytic reactivity with their physical, chemical, and surface properties. It was found that, for both synthesized and commercial sulfated zirconia catalysts, the increase of calcination temperature resulted in the increase of monoclinic phase in sulfated zirconia, and the decrease of acid sites. According to the catalytic reactivity, at high calcination temperature, lower CO conversion, but higher isobutene production selectivity was observed from commercial sulfated zirconia. As for synthesized sulfated zirconia, the isobutene production selectivity slightly decreased with increasing calcination temperature, whereas the CO conversion was maximized at the calcination temperature of 600°C. We concluded from the study that the difference in the calcination temperatures influenced the catalytic performance, sulfur content, specific surface area, phase composition, the relative intensity of Zr3+, and acid–base properties of the catalysts. [Copyright &y& Elsevier]

Abstract: Nanocrystalline zirconia was prepared by decomposition of zirconium tetra n-propoxide in 1,4-butanediol and was employed as a support for cobalt catalysts. The activity and the selectivity of the catalysts in CO hydrogenation were compared with cobalt supported on commercial available micron- and nano-sized zirconia. The catalytic activities were found to be in the order: Co/ZrO2-nano-glycol≫Co/ZrO2-nano-com>Co/ZrO2-micron-com. Compared to the micron-sized zirconia supported one, the use of commercial nano-sized zirconia resulted in higher CO hydrogenation activity but lower selectivity for longer chain hydrocarbons (C4–C6), whereas the use of glycothermal-derived nanocrystalline zirconia exhibited both higher activity and selectivity for C4–C6. The better performance of the latter catalyst can be ascribed to not only the effect of the crystallite size but also the presence of pure tetragonal phase of zirconia. [Copyright &y& Elsevier]

Abstract: In the present study, nanocrystalline χ-Al2O3 were prepared by thermal decomposition of fine gibbsite (χ-GB) and solvothermal method (χ-SV) and employed as supports for preparation of 20wt% Co/Al2O3 catalysts. As compared to the use of γ-Al2O3 with similar BET surface area, Co dispersion and CO hydrogenation activity were higher on the nanocrystalline χ-Al2O3 supported Co catalysts. The transmission electron microscopy (TEM) results revealed that the wrinkled sheets-like structure of γ-Al2O3 was completely destroyed after CO hydrogenation for 6h whereas the spherical particles of χ-SV and plate-like structure of χ-GB were maintained. The H2-temperature program reduction (H2-TPR) also revealed a stronger interaction between cobalt and alumina supports for the Co/χ-Al2O3 catalysts. [Copyright &y& Elsevier]