Ru–Ni Catalyst in the Combined Dry-Steam Reforming of Methane: The Importance in the Metal Order Addition

Abstract

Biogas is one of the main biomass-energy resources. Its use for syngas production with a H 2 /CO ratio close to 2 would have huge environmental, social and economic impact in the actual energetic scenario. However, the use of dry reforming, where the two main components are transformed into syngas, does not allow the desired H 2 /CO ratio. For this reason, the addition of water is proposed. The process was performed with two Ru-Ni catalysts where the metal order in the impregnation process was varied. The catalysts were prepared either by simultaneous or consecutive impregnation of the active phases and its catalytic performance in the combined dry-steam reforming of methane was tested. The catalysts were characterized by FRX, XRD, S BET , TPR-H 2 and Raman spectroscopy. The existence of a strong Ni-Ru interaction is evidenced by Raman spectroscopy and TPR-H 2 in the sample synthesized by the simultaneous impregnation. Concerning the catalytic activity, this sample presents the higher CH 4 and CO 2 conversion values in the entire composition rate and the lowest amount of carbon deposits after reaction. After pulse, and reactivity tests it was concluded that the higher Ni-Ru interaction displayed by the catalyst synthesized by the simultaneous impregnation, enhances the carbon gasification.

CO2 reforming of methane over Ni-Ru supported catalysts: On the nature of active sites by operando DRIFTS study

“…This behavior has been previously reported by our group and denotes a high RuO2-NiO interaction [19]. Fig.4 shows the CO2-CH4 conversions and the H2/CO molar ratio obtained as a function of time at each temperature for the three catalysts studied.…”

“…We would like to emphasize here the rate for RWGS is higher than methane decomposition, and thus the RWGS reaction achieve rapidly the equilibrium [37]. This order for DRM reactivity is opposite to the results previously reported for the combined steam-dry reforming in which the bimetallic Ni-Ru catalyst presented the highest catalytic activity [19]. It is generally accepted that the reaction of steam reforming of methane (SRM) proceeds via dehydrogenation of methane to form surface carbon which is oxidized by adsorbed oxygen generated from water dissociation [38] The thermodynamics of SRM favors the formation of nickel oxide and the role of Ru on the Ni-Ru alloy is to activate the hydrogen produced by the dehydrogenation of CH4 through a spillover effect enhancing the reduction of Ni 2+ species originally present or formed over the catalysts [39].…”

“…Nevertheless, when Ni catalysts are modified with small amounts of another metal, a lot of attention have been paid to the preparation method. In this sense, we have previously demonstrated how the metal order addition have a huge influence in a bimetallic Ni-Ru catalyst when performing the combined steam-dry reforming of methane [19].…”

Tuning combined steam and dry reforming of methane for “metgas” production: A thermodynamic approach and state-of-the-art catalysts

“…As for Pt-coverage and formation of core-shell like derived structures, bimetallic systems of Ni-Ru also tend to interact in the form of clusters with surfaces mainly covered by Ni leading in increased dispersion of Ni 0 particles shown to favor the formation of reactive intermediate C (s) -based species (known to initiate CO generation) under combined reforming reactions [72] . These structures, with optimum synergetic effects, are obtained upon manipulating the order of metal deposition during catalyst synthesis.…”

Does shaping catalysts modify active phase sites? A comprehensive in situ FTIR spectroscopic study on the performance of a model Ru/Al2O3 catalyst for the CO methanation

“…However, the existence of defects induces the presence of under coordinated cations, which results in almost amorphous surface containing an enormous variety of coordination environments for the Al 3+ cations [30,31]. According to Onfroy et al [32], the band at 3760-3780 cm -1 is ascribed to type I terminal hydroxyl (Al 5c ) and those at 3730-3735 and 3700-3710 cm - [34], which is in accordance with early studies on the interaction of CO with single crystal Ru surfaces [35]. The interaction of adsorbed CO on Ru sites with OH groups of the support [36] may result in the formation of adsorbed carboxyl species that are known to be a key intermediate in the WGS reaction (eq.…”