Evaluation of gold on alumina catalyst deactivation dynamics during α-pinene isomerization

Synthesis of camphene is an important step in an industrial process for camphor production from α-pinene. Compared to conventional way of α-pinene to camphene transformation over acid-hydrated TiO2, gold on alumina catalyst was found to provide α-pinene isomerization conversion up to 99.9% and selectivity 60–80% making this catalyst very promising from an industrial viewpoint. However, deactivation of gold catalyst might be a serious obstacle for real industrial implementation. According to TPO and UV–vis-mass in situ it was shown that deactivation is caused by adsorption of hydrocarbons on the gold species. The dynamics of catalyst deactivation during α-pinene isomerization was presented based on a so-called “separable” deactivation model assumption. Effects of isomerization temperature, initial α-pinene concentration and gas atmosphere on catalyst deactivation with time-on-stream were investigated experimentally and correlated with the proposed deactivation function. The results showed that the α-pinene concentration was the major factor governing the deactivation of Au/γ-Al2O3 catalyst under substrate-feeding conditions. When the α-pinene concentration was controlled at a relatively low level such as 0.4 vol.%, especially in hydrogen atmosphere, the total deactivation rate was negligible. An equation of the reaction rate taking into account the catalyst deactivation was suggested making prediction of deactivation behavior in α-pinene conversion at different initial concentrations.