Steam reforming of acetic acid with seawater and pure water over Ni/carbonate catalysts with leachable carriers for recovery of coke

Formation of coke is hardly avoided in steam reforming and some coke of nanotube form could be recovered as functional carbon materials, but this requests their efficient separation from catalyst. Herein, carbonate-supported nickel catalysts (Ni/Na2CO3 and Ni/K2CO3) Ni/CaCO3) were prepared for reforming of acetic acid with seawater and pure water, respectively. The use of water-soluble Na2CO3 and K2CO3 carriers could achieve facile recovery of carbonates, coke and nickel via further acid leaching. The results indicated that K2CO3/Na2CO3 of higher activity for cracking and stronger alkalinity for enhanced CO2 adsorption/activation rendered nickel catalyst of superior activity to that with CaCO3 for seawater reforming. However, salts from seawater gradually blocked active sites, leading to lower catalytic activity (H2 yields: 78% from seawater reforming versus 92% from steam reforming over Ni/CaCO3). Moreover, seawater led to conversion of K2CO3/Na2CO3 carriers into KCl/NaCl, resulting in re-dispersion of nickel and serious catalyst deactivation. CaCO3 was largely immune to such reactions and thus showed lower propensity towards coking (coke content of 48.0 wt% in spent catalyst versus ca. 57% over Ni/Na2CO3 and Ni/K2CO3). In-situ IR characterization of reforming process showed that K2CO3 as a carrier promoted gasification to form oxygenated intermediates (i.e. C=O, C-O-C) as precursors to form coke of aliphatic nature, while CaCO3 facilitated deoxygenation and aromatization, forming coke of more graphitic nature.