CH_4 DRY REFORMING WITH CO_2: CHARACTERIZATION OF SURFACE CARBON SPECIES FORMED ON CeO_x-ZrO_y BASED Ni, Ni-Co AND Ni-Rh CATALYSTS

摘要

Methane dry reforming with CO_2 is greatly affected by the presence of various formof surface carbon (carbides, graphite, carbon nanotubes (CNT), etc). To characterizethem two methods have been chosen: (i) temperature programmed oxidation (TPO) and(ii) transmission electron microscopy (TEM). CeZrNi, CeZrNiCo, CeZrNiRh and 5%Ni/CeZrcatalysts were prepared by sol-gel and impregnated method, respectively. Thesecatalysts are efficient in dry reforming of methane reaction. The surface carbon obtainedduring the reforming process was generally characterized by Tmax in TPO. On sol/gelCeZrNi(s/g) and impregnated Ni/CeZr(imp.) catalysts the Tmax appeared at 400oC and at600oC, respectively, which shows different carbon structures. Simultaneously, TEMimage pointed out the extensive CNT formation on the impregnated Ni catalyst alongwith an increase in Ni particle size while for the sol/gel sample the Ni particles arestabilized in the form of Ni nanoparticles. On bimetallic CeZrNiCo(s/g) and CeZrNiRh(s/g)catalysts two kinds of surface carbon species coexist. These characterized by Tmax at360°C was slowly transformed to those at higher temperature peak (600°C). Theamount of carbon is considerably higher on the Co containing sample than for one withRh. We can speculate that on CeZrNiCo sample the carbidic (CoC_x or NiC_x) species arepredominantly formed and after the changing of catalyst structure the CNT and graphiticspecies become prevailing.