Effect of the Ni/Al ratio of hydrotalcite-type catalysts on their performance in the methane dry reforming process

Abstract

Hydrotalcite-type solids of the form NiAl-R, where R refers to the ratio of Ni to Al (R = 2, 3, 5, 8, and 10), were successfully synthesized following co-precipitation method at pH = 12. The obtained solids were calcined at 800°C, except for NiAl-R 2 where calcination was performed at temperatures ranging between 300 and 800°C. Following calcination, the resulting materials were evaluated for their catalytic activity and stability during the process of dry reforming of methane. Factors affecting the catalytic activity of the obtained materials such as the ratio R and calcination temperature were also studied. Prior to calcination, X-ray diffraction analyses clearly illustrated the typical hydrotalcite structure of the synthesized materials (when R B 5). On the other hand, calcination at various temperatures prompted decomposition of all solids to form NiO, with exception to NiAl-R 2 , which upon calcinations at 800°C was decomposed to form NiO and a second phase spinel containing NiAl 2 O 4 . The chemical composition of the obtained solids was determined by atomic absorption spectroscopy. Further characterization was performed using several techniques, including: surface area measurements (S BET ), scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. The reducibility of nickel species was studied via temperatureprogrammed reduction. The catalytic performance of the asprepared samples was studied for dry reforming of methane under atmospheric pressure at temperatures ranging between 400 and 700°C. The catalytic activity of the designed substances highlighted the importance of molar ratios i.e. Ni 2? / Al 3? on the success of the overall dry reforming of methane process. The catalytic activity of the synthesized materials was also found to be directly proportional to the ratio of Ni/ Al as well as the calcination temperature, with exception to NiAl-R 2 which was found to exhibit the highest activity of all. The latter observation was perhaps associated with the lower size of the crystalline particles in conjunction with the presence of a second phase containing NiAl 2 O 4 . In this study, it is shown that the calcination temperature has a significant effect on the catalytic property and the crystallite size of the metal.

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

“…by Ni 2? cations in the brucite-like layers in comparison to naturally occurring hydrotalcite mineral with chemical formula of Mg 6 Al 2 (OH) 16 CO 3 Á4H 2 O. In this work, the obtained hydrotalcite materials were promoted with Ce species via adsorption from the aqueous solution of [Ce(EDTA)] -complexes.…”

“…Recently, a lot of attention has been paid to the study of to hydrotalcite-derived materials as possible catalysts for DRM [12][13][14][15][16][17][18]. To improve the stability of the Nibased catalysts, various promoters were proposed.…”

A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane

“…With respect to the influence of Ni loading and/or Ni/Al ratio, Touahra et al [61] prepared hydrotalcite-derived Ni/Al mixed oxides using different Ni/Al molar ratios (2, 3, 5, 8, 10), which were subsequently tested in DRM within the temperature range of 400-700 • C. They observed an important influence of the calcination temperature, since NiAl 2 O 4 spinel phase was detected in the catalysts calcined at 800 • C, this fact being, according to the authors, the main reason for the higher stability of these materials in DRM. Moreover, the catalyst prepared using a Ni/Al ratio equal to 2 was showing the best overall catalytic performance.…”

“…A summary of different works considering and discussing the effect of calcination temperature in the DRM performance of hydrotalcite-derived catalysts is presented in Table 3. NiAl HT/CP 300, 400, 500, 600, 700 and 800 • C for 6 h Calcination temperature <500 • C has minimal effect of activity; Increase in calcination temperature resulted in increased activity and stability [61] NiMgAl HT/CP 400, 600, 800 • C for 6 h Calcination temperature had a small influence on the activity and selectivity [54] NiMgAl HTsSG 500, 650 • C for 5 h…”

“…Higher calcination temperature resulted in the increased stability [56] NiMgAl HT/CP 500, 600, 700, 800 • C for 6 h No significant effect of calcination temperature on performance in DRM was observed [76] NiMgAl HT/CP 350, 600, 800, 1000 • C Calcination at 800 and 1000 • C resulted in formation of spinel phase. The optimal calcination temperature was selected to be 600 • C [67,68] Thouahra et al [61] examined the influence of the calcination temperature on the performance of Ni/Al catalysts. They concluded that the use of calcination temperatures below 500 • C did not practically affect the catalytic activity.…”