Kinetics and Mechanism of Acetalisation of Furfural to Furfural Diethyl Acetal with Ni–Al Layered Double Hydroxides Containing Lewis Acid Sites

The nitrate form of Ni–Al layered double hydroxide (denoted as Ni–Al–NO₃-LDH) and the corresponding carbonate form (denoted as Ni–Al–CO₃-LDH) were tunably fabricated by the hexamethylenetetramine hydrolysis method. A catalytic behaviour investigation proved Ni–Al–CO₃-LDH to be an ineffective catalyst, while for Ni–Al–NO₃-LDH excellent catalytic activity and reusability were obtained, in the acetalisation of furfural to furfural diethyl acetal. Characterisation and analysis revealed that the appearance of Lewis acid sites in Ni–Al–NO₃-LDH was responsible for its excellent catalytic performance. The acquired kinetic parameters confirmed that this reaction was a first-order process and the apparent activation energy was 36.28 kJ mol⁻¹, which is in reasonable agreement with the theoretical result of 38.57 kJ mol⁻¹. Additionally, apart from the typical Brønsted acid catalytic mechanism, a possible Lewis acid catalytic mechanism was probed theoretically.