Enhancement of indoles production and catalyst stability in thermo-catalytic conversion and ammonization of furfural with NH3 and N2 environments

Abstract

Thermo-catalytic conversion and ammonization (TCC-A) is a novel and promising thermochemical conversion process for the direct production of N-heterocycles under NH3 atmosphere, which is similar to the pyrolysis technology through introducing exogenous nitrogen. Since NH3 served as the carrier gas and reactant, it played an important part in the process. The introduction of N2 into NH3 significantly enhanced the indoles production and catalyst stability in the TCC-A process of bio-derived furans. Under the optimized TCC-A conditions of furfural, NH3 being diluted by 25% N2 at 600°C with WHSV as 1.5h−1 and gas flow rate at 40ml/min, the carbon yields of N-containing chemicals and indoles reached 46.51% and 33.04%, respectively, which increased by 90.54% and 203.96% compared with those in pure NH3. Using furan derivatives as the feedstock, diluted NH3 also showed positive effect on the production of N-containing chemicals. Functional groups in the furan derivatives strongly affect the product distribution. It was found that the increase of indoles production from furfural was because the generation of 2-furonitrile via the side reaction pathway to form coke was inhibited by the dilution of NH3. The catalysts were tested via five reaction/regeneration cycles in pure and diluted NH3 atmosphere and characterized by N2 adsorption/desorption, XRD, XRF, NH3-TPD analyses and SEM. Compared in pure NH3, the catalysts in N2 diluted NH3 was more stable, which could be due to the lower degree of dealumination, structure damage, and acid site loss.