The Effect of WO3 Modification of ZrO2 Support on the Ni-Catalyzed Dry Reforming of Biogas Reaction for Syngas Production

Abstract

The time-on-stream catalytic performance and stability of 8 wt. % Ni catalyst supported on two commercially available catalytic supports, ZrO 2 and 15 wt.% WO 3 -ZrO 2 , was investigated under the biogas dry reforming reaction for syngas production, at 750 • C and a biogas quality equal to CH 4 /CO 2 = 1.5, that represents a common concentration of real biogas. A number of analytical techniques such as N 2 adsorption/desorption (BET method), XRD, H 2 -TPR, NH 3 -and CO 2 -TPD, SEM, ICP, thermal analysis (TGA/DTG) and Raman spectroscopy were used in order to determine textural, structural and other physicochemical properties of the catalytic materials, and the type of carbon deposited on the catalytic surface of spent samples. These techniques were used in an attempt to understand better the effects of WO 3 -induced modifications on the catalyst morphology, physicochemical properties and catalytic performance. Although Ni dispersion and reducibility characteristics were found superior on the modified Ni/WZr sample than that on Ni/Zr, its dry reforming of methane (DRM) performance was inferior; a result attributed to the enhanced acidity and complete loss of the basicity recorded on this catalyst, an effect that competes and finally overshadows the benefits of the other superior properties. Raman studies revealed that the degree of graphitization decreases with the insertion of WO 3 in the crystalline structure of the ZrO 2 support, as the I D /I G peak intensity ratio is 1.03 for the Ni/Zr and 1.29 for the Ni/WZr catalyst.

Investigating the correlation between deactivation and the carbon deposited on the surface of Ni/Al2O3 and Ni/La2O3-Al2O3 catalysts during the biogas reforming reaction

“…8a and 8b) exhibited a peak shape typical of sp 2 hybridised carbon, confirmed by the D-parameter value (derived from the first derivative of the C KLL Auger peak in the XPS spectrum)[72] being 19.6 -20.4 in all cases. These results are in accordance with the literature, as it has been reported that the carbon deposition can be significantly suppressed due to the interaction between Ni particles and lanthana species in Ni based Al 2 O 3 catalyst modified by La 2 O 3[44,73].…”

“…Furthermore, despite the same Ni loading in the two catalysts herein, the La-modified catalyst exhibits higher surface Ni concentration compared to the La-free catalyst (Table 2). This is in agreement with the literature, where La, Ca and Mg addition as support modifiers have been reported to improve Ni dispersion[44,68,69]. Also, as the temperature of reaction increases to 800 o C, the relative concentration of Ni 0 compared to oxidized Ni is increased.…”

“…As mentioned above, the Ni/Al and Ni/LaAl catalysts in their calcined and/or their reduced form were characterized by N 2 adsorption/desorption, ICP, XRD, NH 3 -TPD, CO 2 -TPD and H 2 -TPR, while the calcined supports were characterized by PZC/PMT, XRD, BET and H 2 -TPR. The main findings of these characterization techniques will be summarized in this section, as they will be used below in explaining catalytic performance and/or carbon deposition; a detailed discussion can be found in [43,44]. (Fig.…”

“…Grace), we confirmed that the basic character of lanthanum oxide (La 2 O 3 ) has promotional effects for nickel based catalysts in the DRM. In separate work [44] we also argued that the modification of alumina with lanthana facilitates the dispersion of active species, strengthens the interactions between nickel species and support, increases the population of basic sites, and helps redistribute the acid sites in terms of strength and density. Promotional effects induced by the incorporation of lanthana into the alumina support have also been reported by other researchers.…”

The Relationship between Reaction Temperature and Carbon Deposition on Nickel Catalysts Based on Al2O3, ZrO2 or SiO2 Supports during the Biogas Dry Reforming Reaction

“…Another key property of the supporting materials is basicity, as the formation of carbon from methane decomposition Equation (3) is known to occur over the acid sites of the support [20]. Increased basicity also leads to the activation of CO 2 , which helps to oxidize the deposited carbon Equation (8) [21]. Moreover, CO 2 activation and the oxidation of carbon to CO Equation (6) depend on the oxygen storage capacity (OSC) of a support [22].…”