Global Vision of the Reaction and Deactivation Routes in the Ethanol Steam Reforming on a Catalyst Derived from a Ni–Al Spinel

Abstract

Ethanol steam reforming (ESR) over a Ni/Al 2 O 3 catalyst prepared by reduction of a NiAl 2 O 4 spinel is a promising alternative route to produce H 2 from biomass. This work deepens into the effect of reaction conditions (450−650 °C, a steam/ ethanol (S/E) ratio of 3−9, and a weight space time up to 1.3 h) and evaluates the time on stream evolution of the yields of H 2 , gaseous byproducts (CO, CO 2 , CH 4 , C 2 H 4 , C 2 H 4 O), and formed carbon/coke. The results are explained taking into consideration the thermodynamics, the extent of each individual reaction, and the catalyst deactivation. Up to 600 °C, the predominant intermediate in the H 2 formation is C 2 H 4 (formed by ethanol dehydration) with the preferential formation of nanostructured carbon (nanotubes/ filaments) by C 2 H 4 decomposition. The deposition of this type of carbon partially deactivates the catalyst, mainly affecting the extent of the C 2 H 4 decomposition causing a sharp decrease in the H 2 and carbon yields. Nevertheless, the catalyst reaches a pseudosteady state with an apparent constant activity for other reactions in the kinetic scheme. At 650 °C, C 2 H 4 O (formed by the ethanol dehydrogenation) is the main intermediate in the H 2 formation, which is the precursor of an amorphous/turbostratic carbon (coke) formation that initially causes a rapid deactivation of the catalyst, affecting the ethanol dehydration and, to a lower extent, the reforming and water gas shift reactions. The increase in the S/E ratio favors the H 2 formation, attenuates the catalyst deactivation due to the suppression of the ethanol dehydration to C 2 H 4 , and promotes the reforming, water gas shift, and carbon/coke gasification reactions. A H 2 yield of 85% stable for 48 h on stream is achieved at 600 °C, with a space time of 0.1 h and an S/E ratio of 9.