The effect of catalyst preparation conditions on the synthesis of menthol from citronellal on Ru/H-BEA

• Ru/H-BEA enables one-pot cyclization-hydrogenation tandem reaction of citronellal to menthol.
• Excellent menthol yield of 92%.
• Ru precursor and reduction temperature are important catalyst preparation variables.

Heterogeneous Ru/H-BEA catalysts are suitable catalysts for the one-pot transformation of citronellal to menthols, which requires a combined cyclization-hydrogenation step. Here, we report the role of different preparation conditions-namely the choice of the Ru-precursor (Ru(NO)(NO3)3), Ru(acac)3, RuCl3 and Ru3(CO)12) as well as the reduction temperature (523–923 K) of the catalyst. Using Ru(NO)(NO3)3 as precursor the highest activity was obtained, while the product distribution was not strongly affected by the choice of the precursor.On the contrary the reduction temperature leads to very different product distributions: Increasing it from 623 K to 923 K for a 1%Ru/H-BEA-25 catalyst the competitive hydrogenation of citronellal was diminished, which leads to an increased selectivity to menthols from 77% to 87% and additional the activity increases with a factor of 3.4. This behaviour might be due to a dealumination of the zeolite during reduction at higher temperatures. Moreover, in combination with appropriate reaction conditions a yield to menthols of 92% can be reached.

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