Ni-loaded catalyst containing ZSM-5 zeolite for toluene hydrogenation

Nickel catalysts (8 wt.% of NiO) containing ZSM-5 and aluminium hydroxide (1:1) were tested for activity in the hydrogenation of toluene. The catalysts differed in the extent of zeolite ion exchange. The hydrogenation activity of the catalyst was modified by additional incorporation of 4 wt.% of NiO or 0.2 and 0.4 wt.% of RuO2. Experiments were carried out in a continuous-flow system at 3.5 MPa and 160-320 °C (LHSV = 3 h−1; H2:CH = 350 Nm3/m3). It was found that conversion of toluene over the nickel-loaded catalysts increased noticeably (by 35-60%) when the amount of NiO incorporated by impregnation rose from 8 to 12 wt.%. The occurrence of side-reactions observed at higher temperatures can be reduced by increasing the metal to Brønsted acid ratio of the catalysts. A correlation was also found between the selectivity of direct hydrogenation products and the metal to Brønsted acid ratio. The increase of this ratio reduced the selectivity of cyclopentane derivatives and raised their methylcyclohexane selectivity, especially at reaction temperature above 200 °C. The modification of the 8 wt.% NiO catalyst by the addition 0.2 wt.% of RuO2 yielded a catalyst of an activity allowing toluene hydrogenation at a considerably lower temperature as compared to the 12 wt.% NiO catalyst; the selectivity of these catalysts was comparable. When the amount of RuO2 was increased from 0.2 to 0.4 wt.%, this accounted for only a slight improvement in activity and selectivity of catalyst.