The study employs Na₂CO₃ as a Ni catalyst support or modifier for Ni/SiO₂ catalysts in steam reforming of acetic acid, demonstrating its novel function as an additive that inhibits carbon deposition via enhanced gasification of coke precursors.

Abstract

Alkaline salts like Na₂CO₃ are known as effective catalysts for enhancing cracking in biomass gasification. They might be also active for gasifying coke or precursors of coke in reforming of small organics, which was investigated herein by conducting steam reforming (SR) of acetic acid over Ni/Na₂CO₃ and Na₂CO₃-modified Ni/SiO₂ catalysts. The results demonstrated that Ni-15Na₂CO₃/SiO₂ with higher loading of Na₂CO₃ exhibited significantly improved catalytic activity (hydrogen yield: ca. 80% over Ni-15Na₂CO₃/SiO₂ vs. >ca. 65% over Ni/SiO₂ at 600 °C) and catalytic stability. Measurement of reaction intermediates in SR with in situ IR confirmed enhanced adsorption/dissociation of steam to ─OH and accelerated gasification of carbonaceous intermediates, particularly aliphatic organics like ─C─H and C═O functionalities. This resulted in accumulation of less coke (45.8% for Ni-15Na₂CO₃/SiO₂ and 46.7% for Ni/Na₂CO₃ vs. 77.0% for Ni/SiO₂). Nonetheless, coke formed in Ni/Na₂CO₃ was more aliphatic, originating from incomplete gasification of carbonaceous species with steam, and forming coke of amorphous structure. Highly dispersed Na₂CO₃ in Ni-15Na₂CO₃/SiO₂ could effectively gasify aliphatic components, forming coke of higher aromatic degree in carbon nanotube form with more defective structures and less oxygen in carbon skeleton.