Ti 3 C 2 MXenes-based catalysts for the process of α-pinene isomerization.

In this study, the catalytic performance of Ti 3 C 2 MXene materials in the reaction of α-pinene isomerization was demonstrated. The influence of etching agents (HF, HF/H 2 SO 4, and HF/HCl; weight ratios of mixed acids: 1 : 3, 1 : 4, and 1 : 5) on removing Al atoms from MAX phase, creation of an accordion-like structure typical for MXenes and catalytic activity of the produced samples have been revealed. The MXene HF obtained by MAX phase HF treatment exhibited the highest activity (conversion of α-pinene 74.65 mol%), while materials produced with the mixed acids (HF/H 2 SO 4 and HF/HCl) showed a significant reduction in the conversion of α-pinene (on average about 28-fold). However, these last samples displayed an increase of about 10 mol% in the selectivity to the most desirable product-camphene. The high activity of MXene HF is a result of a high concentration of acid sites (11.62 mmol g -1 ) - the concentration of acid sites in the samples obtained by MAX phase mixed acids treatment was about 2.5-5.5 times smaller. This work proposes possible mechanisms for the α-pinene isomerization reaction on the MXene HF and on the MXene HF/H 2 SO 4 X  :  Y and MXene HF/HCl X  :  Y in connection with their structure.