Selective dehydroisomerization of cyclic monoterpenes to p-cymene over silica-supported CdO

Cadmium oxide supported on silica is a highly active and selective bifunctional catalyst for the clean synthesis of p-cymene using dehydroisomerization of cyclic monoterpenes such as α-pinene, β-pinene, limonene, α-terpinene, γ-terpinene, and terpinolene. The dehydroisomerization occurs via acid-redox bifunctional catalysis at the gas-solid interface involving isomerization of monoterpenes to p-menthadienes on acid sites of silica support followed by p-menthadiene dehydrogenation to p-cymene on oxo-metal sites of CdO. The less reactive bicyclic monoterpenes, such as α-pinene and β-pinene, give 91–95% p-cymene yields at 325–375 °C, whereas more reactive monocyclic monoterpenes, such as limonene, α-terpinene, γ-terpinene, and terpinolene, give a 100% yield at 200–250 °C. To the best of our knowledge, CdO/SiO2 has the highest efficiency in monoterpene-to-p-cymene dehydroisomerization among the catalysts reported so far. The catalyst was characterized by BET, TGA, XRD, DRIFTS, H2-TPR, and ICP–OES

Dehydroisomerisation of alpha-Pinene and Limonene to p-Cymene over Silica-Supported ZnO in the Gas Phase

Silica-supported zinc oxide possessing acid and dehydrogenation functions is an efficient, noble-metal-free bifunctional catalyst for the environment-friendly synthesis of p-Cymene from renewable monoterpene feedstock by gas-phase dehydroisomerisation of α-pinene and limonene in a fixed-bed reactor. The reaction involves acid-catalysed terpene isomerisation to p-menthadienes followed by dehydrogenation to form p-Cymene. Dehydroisomerisation of α-pinene produces p-Cymene with 90% yield at 100% conversion at 370 °C and WHSV = 0.01–0.020 h−1. The reaction with limonene gives a 100% p-Cymene yield at 325 °C and WHSV = 0.080 h−1. ZnO/SiO2 catalyst shows stable performance for over 70 h without co-feeding hydrogen

Probing the Catalytic Efficiency of Supported Heteropoly Acids for Esterification: Effect of Weak Catalyst Support Interactions

Supported heteropoly acids are an interesting class of solid acid catalysts which possess flexible structure and super acidic properties essentially required for the oil-based biodiesel production. In this study, a series of catalysts containing 25 wt.% of heteropolytungstate (HPW) supported on various clays or SiO2 were prepared, and their catalytic efficiency was evaluated for esterification of acetic acid with heptanol. The as-prepared catalysts were characterized by various techniques including FT-IR spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and BET. The catalytic efficiency of both bulk and supported HPW catalysts for the esterification activity strongly depends on the type of support and amount of catalyst; the bulk HPW catalyst and the catalyst supported by kaolinite with 25 wt.% of HPW exhibited highest activity. In order to study the effect of temperature on conversion, all the catalysts were subjected to different reaction temperatures. It was revealed that esterification activity of both bulk and supported HPW catalysts strongly depends upon the temperature variations of the reaction. Besides, the effect of leaching of active sites on the catalysts performance for biodiesel production was also evaluated by inductively coupled plasma studies (ICP). The kaolinite-supported catalyst (25% HPW/kaolinite) demonstrated higher amount of leaching which is also confirmed by the significant decrease in its catalytic activity when it is used for the second time. However, the higher activity demonstrated by HPW/kaolinite maybe because of some homogeneous reaction indicating a weak catalyst support interaction (WCSI) resulting in the leaching of the catalyst during the test. Furthermore, the effects of other reaction variables such as catalyst loading and reaction time on the conversion of acetic acid were also studied