Catalytic activity of hydrotalcite-derived catalysts in the dry reforming of methane: on the effect of Ce promotion and feed gas composition

Abstract

Ni/Al and Ni/Mg/Al hydrotalcite-derived materials containing various Ni loadings were synthesized and subsequently promoted with Ce-species via adsorption from [Ce(EDTA)] -complexes. The obtained materials were characterized by elemental analysis (ICP-MS), XRD, H 2 -TPR, CO 2 -TPD, TG and low temperature N 2 sorption experiments. The amount of the introduced Ce was dependent on the nickel and magnesia content in catalysts precursors, and it influenced materials properties (i.e. basicity, reducibility of Ni species) in various ways and the catalytic performance in the dry reforming of methane (DRM). The promoted catalysts showed improved performance with CH 4 and CO 2 conversions at 550°C in the range of 35-55 and 35-45%, respectively. The extent of the improvement was dependent on the nickel content and the presence of magnesia. In general, Ce promotion increased materials stability by changing of the type of carbonaceous deposits. Ce modification hindered the transformation of amorphous carbonaceous deposits to graphitic carbon. The former may be easier oxidized and contribute to syngas production. Two selected catalysts were additionally tested in DRM at elevated temperatures (650 and 750°C) and over various feed gas compositions.

Highly Carbon-Resistant Y Doped NiO–ZrOm Catalysts for Dry Reforming of Methane

“…A similar phenomenon can be observed in our group's previous works [37,40]. According to the literature [10,38,39], the weak and medium-strength basic sites can promote the formation of activation carbonate species, thereby enhancing the ability to remove the carbon deposition. Whereas, too strong basic sites lead to too strong CO 2 adsorption, thereby promoting more carbon deposition.…”

“…The total number of basic sites increases from 73 to 100 µmol CO 2 /g on the NiO-ZrO m catalyst before and after the introducing of yttrium (see in Table 2), which indicates that the yttrium can enhance the total number of basic sites. As already described elsewhere [37][38][39], there are three types of basic sites (weak, medium-strength and strong). The content of weak peak on the NiO-ZrO m -YO n catalyst (36.9%) is higher than that on the NiO-ZrO m catalyst (15.5%), while the content of the strong peak decreases to 13.0% on the NiO-ZrO m -YO n catalyst.…”

Ce- and Y-Modified Double-Layered Hydroxides as Catalysts for Dry Reforming of Methane: On the Effect of Yttrium Promotion

“…According to Daza et al [12], 3 wt.% of Ce had a positive effect on carbon removal, and it was reported as an optimal content in Ni-based hydrotalcites. Also, as observed by Dębek et al [15], less graphitic carbon was formed in Ce-modified Ni-DLHs, in favor of the amorphous carbon which can be gasified during DRM [14]. In the other study of Daza et al [13], the co-precipitation with cerium nitrate (assuming different ratios of Al/Ce, i.e., 1.5, 4.0, 9.0 and 24.0) resulted in the best catalytic performance at 700 • C for the catalyst with the highest Al/Ce ratio.…”

“…This distance remained stable after promotion with cerium and cerium/yttrium. The c' relates to the distance between two layers plus one brucite-like sheet, and the values suggest the presence of CO 3 2− (7.65 Å) and NO 3 − (8.79 Å) ions [6,14]. Additionally, a separate phase of ceria is revealed in XRD diffractograms ( Figure 1).…”

“…After the thermal treatment in hydrogen, nickel oxides are reduced to metallic nickel, which is located on the surface of the catalyst and can react with CH 4 in DRM [3]. This kind of catalysts were reported as active and selective in dry reforming of methane [8][9][10][11], however, a significant improvement in their performance can be observed after promotion with metals, such as Ce, Zr, Y, La, or Zn [4,[12][13][14][15][16][17][18][19]. Modification with ceria was described as beneficial in dry reforming of methane, due to oxygen storage capacity and redox properties of Ce [13][14][15][20][21][22].…”