Effect of calcination temperature on characteristics of sulfated zirconia and its application as catalyst for isosynthesis

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.     

Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

A Comparative Study of Ethylene/α-Olefin Copolymerization with Silane-Modified Silica-Supported MAO Using Zirconocene Catalysts

Activities of ethylene/α-olefin copolymerization were found to increase with silane-modified silica-supported MAO using ansa-zirconocene catalyst. The increase in activities was less pronounced when higher α-olefins were used. However, silane modification resulted in the narrower molecular weight distribution of polymers. ¹³C NMR revealed that ethylene incorporation in all systems gave polymers with the similar triad distribution.     

Observation on Different Turnover Number in Two-phase Acid-catalyzed Esterification of Dilute Acetic Acid and 1-Heptanol

This paper reports on the two-phase acid-catalyzed esterification of dilute acetic acid and 1-heptanol. It reveals larger turnover number of the Amberlyst 15 than sulfuric acid. It indicates that adsorbed water on protonated sites is replaced by acetic acid, then moving into the organic phase to promote the reaction.     

Effect of Ga modification on different pore size silicas in synthesis of LLDPE by copolymerization of ethylene and 1-hexene with [<Emphasis Type="Italic">t</Emphasis>-BuNSiMe<Subscript>2</Subscript>Flu]TiMe<Subscript>2</Subscript>/MMAO catalyst

Copolymerization of ethylene and 1-hexene for obtaining the linear low-density polyethylene was conducted along with silicas as supports for [t-BuNSiMe₂Flu]TiMe₂/MMAO catalyst. Two silicas with different pore sizes were used to investigate the effect of pore sizes on copolymerization. In addition, gallium was also introduced into both silicas to improve their properties and enhance the catalytic activities of the system. It was found that before modification, the larger pore silica exhibited higher catalytic activity than the smaller one due to low internal diffusion resistance. After modification, both silicas exhibited higher catalytic activity comparing to their pristine condition. However, 1-hexene incorporation in the obtained copolymers was lower. The reduced surface area of silica after modification was the main reason for the decrease in 1-hexene incorporation. The properties of the copolymers by means of differential scanning calorimetry, gel permeation chromatography, and ¹³C NMR spectroscopy were further discussed in more detail.     

Characterization of Cobalt Dispersed on Various Micro- and Nanoscale Silica and Zirconia Supports

Cobalt dispersion on various micro- and nanoscale SiO₂ and ZrO₂ was investigated. It revealed that Co/SiO₂ (M) exhibited higher activity than Co/SiO₂ (N) due to strong support interaction. However, Co/ZrO₂ behaved oppositely. In addition, Co dispersed on the nanoscale SiO₂ and ZrO₂ gave the similar activity for CO hydrogenation because of more uniform species.     

Solvent effect on synthesis of zirconia support for tungstated zirconia catalysts

Solvothermal reaction of zirconium n-butoxide (ZNB) in different solvent media, such as 1,3-pentanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol resulted in the formation of zirconium dioxide (ZrO₂) nanostructure. Then, the 15%W/ZrO₂ (WZ) catalysts using different zirconia supports were prepared by impregnation method. The effects of solvent on preparation of zirconia on the catalytic performance of WZ catalysts in esterification of acetic acid and methanol at 60 °C were investigated. The experimental results showed that ZrO₂ particles prepared in 1,4-butanediol (ZrO₂-BG) have a spherical shape, while in other glycols the samples were irregularly-shaped particles. The reaction results of esterification illustrated that the W/ZrO₂-BG catalysts had high surface acidity and showed high acetic acid conversion. The W/ZrO₂-PeG catalysts (ZrO₂ particles prepared in 1,5-pentanediol, PeG) exhibited the lowest surface acidity among other samples due to strong interaction of proton species and the zirconia supports as proven by TGA. One of the possible reasons can be attributed to different amounts of carbon residue on the surface of catalysts.