Recent studies on aqueous-phase reforming: Catalysts, reactors, hybrid processes and techno-economic analysis

Abstract

Aqueous-Phase Reforming (APR) produces carbon monoxide-free hydrogen (H2) that can be directly applied in polymer electrolyte membrane fuel cells. Oxygenated substrates having C:O = 1:1 are typical feedstocks for APR. A single reactor is required because the water gas shift reaction occurs in-situ, thereby eliminating the cost associated with an additional reactor. The role of the catalyst and support in APR is crucial for achieving high conversion of the substrate and high selectivity towards H2 and/or alkanes. Till date, a variety of catalysts (Pt, Pd, Ru, Re, Rh, Ni, Co, Fe, Cu and Zn) and large number of feedstocks (glycerol, sugars, sugar alcohols, methanol, ethanol, polyols, cellulose and amino acids) were investigated to produce H2 by the APR process. The present review focused on the coupled processes, viz. hydrothermal liquefaction followed by APR, hydrothermal carbonization followed by APR, wet air oxidation (WAO) followed by APR, hydrogenation followed by APR, and in-situ hydrogenation using H2 produced from the APR process. We considered the most recent research articles that reported improved H2 yield using novel catalysts, feedstocks and reactors. Although the focus was on H2 production, the gaseous or liquid alkanes in the fuel-fraction range were also considered wherever appropriate. Along with this, a few articles that reported techno-economic analysis of the APR process were considered too.