Selective production of furan from gas-phase furfural decarbonylation on Ni-MgO catalysts.

Abstract

A series of Ni-MgO catalysts (Ni/Mg molar ratio: 0.1-0.3), prepared by a coprecipitation-calcination-reduction methodology, was characterized and evaluated in the gas-phase hydrogenation of furfural. In all cases, after reduction at 500ºC, nickel species were present as very tiny metal Ni(0) nanoparticles and forming part as Ni(II) of a NiO-MgO solid solution, as inferred from XRD and XPS techniques. The decarbonylation process of furfural was favoured at reaction temperatures as low as 190ºC. The most active catalyst was that with a Ni/Mg molar ratio of 0.25, maintaining a furfural conversion of 96% after 5 h of time-on-stream at 190ºC, by feeding a furfural solution in cyclopentylmethyl ether (5 vol.% furfural) under a H2 stream (H2:furfural molar ratio= 11.5 and WHSV= 1.5 h-1). Furan was the main product, with a yield of 88%, whereas furfuryl alcohol was formed at lower reaction temperature and shorter contact time. However, the catalyst suffers a gradual deactivation during a catalytic test of 24 h, attaining a FUR conversion of 65%, with a furan yield following a similar trend (55%), while FOL was almost negligible (only 6%). The regeneration after calcination led to the sintering of Ni nanoparticles, thus decreasing the furan yield.