Cadmium modified HZSM-5 catalyst (Cd/ZSM-5) prepared by incipient wetness impregnation shows markedly high selectivity of aromatics and low selectivity of light alkanes and C5–C9 nonaromatics in the methanol-to-aromatics (MTA) transformation. The majority of the introduced Cd cations can exchange with protons of the bridged hydroxyl groups of HZSM-5, leading to a reduced number of Brønsted acid sites while generating new Lewis acid sites on the catalysts. The selectivity of aromatics with the Cd/ZSM-5 is found to be linearly correlated with the concentration of the strong Lewis acid sites. Compared to Zn/ZSM-5, the most extensively investigated catalyst thus far for the MTA, Cd/ZSM-5 is found to be more effective in promoting the aromatics formation. The different catalytic behavior observed for Cd/ZSM-5 and Zn/ZSM-5 catalysts is most likely due to the difference in ionic radius of Cd and Zn.

The influence of some transition metal ions including Fe2+, Ni2+, Cr3+, Mn2+, Zn2+, Cd2+ on the catalytic performance of Ru particles during the liquid phase partial hydrogenation of benzene to cyclohexene was investigated in a titanium autoclave and a stainless steel autoclave. The Ru particles were prepared by the precipitation method. The catalysts were characterized using XRD, BET surface area measurement and XPS. The structure configurations and formation enthalpies of the hydrated metal ions, the complexes of the metal ions with benzene and cyclohexene as well as the complexes of hydrated metal ions with benzene and cyclohexene were optimized and evaluated using quantum chemical calculation methods. It was found that the poisoning effect of the transition metal ions on the catalytic activity of Ru particles only partially obeys the “Maxted rule”. The enhancing effect of the transition metal ions on the cyclohexene selectivity is associated with both the interaction of the metal ions with the active sites on Ru surface and with the tendency of metal ions to form hydrated complexes. In the stainless steel autoclave, the Fe2+, Ni2+ and Cr3+ resulted from the corrosion of the stainless steel have a synergetic effect with Zn2+, leading to a higher selectivity to cyclohexene.

In this paper, the reaction kinetics of the oxidation of cyclohexanol by nitric acid to adipic acid (AA) with and without using Cu(II) and V(V) as catalysts was studied in a continuous flow stirred tank reactor at conditions close to the industrial process. Rate equations of power law type and lumping of the reaction intermediates were applied to describe the reaction kinetics. The effect of the catalyst on the selectivity of products including the dicarboxylic acid and the unrecoverable N2 and N2O was investigated. Cu(II) or V(V) alone and the combination of them enhance the selectivity of AA by suppressing the formation of the by-product glutaric acid and succinic acid with Cu(II) being more effective than V(V), and the combination of Cu(II) and V(V) being more effective than Cu(II). In the presence of the catalysts, the consumption of HNO3 and the production of the unrecoverable nitrogen containing compounds per mole of AA are reduced. Based on the experimental results, the way for the catalysts to influence the reaction mechanism was proposed.