Dehydrogenation of a-Limonene

1 Conversion over Unmodified H-ZSM-5 and H-US-Y - The influence of the pore structure of the zeolites on the product distribution of m- and p-cymene isomers has been studied in the presence of an unmodified shape-selective medium pore-sized H-ZSM-5-(55) and the unmodified H-US-Y zeolite at temperatures between 200 and 300 °C. In contrast to the H-US-Y, the p-cymene formation in the presence of H-ZSM-5 is favoured due to the shape selectivity.  

2 Conversion over Pd-modified H-ZSM-5 - Dehydrogenation of a-limonene to cymenes is only obtained in the presence of strong acidic sites of H-ZSM-5 

Cracked products (toluene + lower alkanes, propanes) 28.3 24.3 19.7 11.3 6.3 

3 Conversion over PdICe-modified H-ZSM-5 - A way to promote the noble metal function is the addition of rare earth metals to the catalyst system. It has been reported that rare earth metals can act as anchors for noble metals and thus enhance dispersion and accessibility of noble metal sites in a zeolite. The product distribution for a-limonene conversion over first Ce-exchanged, afterwards Pd-exchanged, H-ZSM-5-(55) is given in Table 7. 

4 Conversion over PdICe-modified Na-ZSM-5 - Surprisingly, employing a non-acidic Na-ZSM-5 as support for Pd catalyst and Ce promotor does not reduce the formation of dealkylated by-products (Table 8). 

---