Low‐Temperature and Highly Active Nickel Catalyst Based on Hydrotalcite Mg–Al for CO₂ Methanation

Abstract

Ni/hydrotalcite catalysts are synthesized by the coprecipitation method. Synthesis times are decreased and activation is performed with just a reductive calcination under mild conditions without the usual air‐calcination step. Compared with the other reported catalysts made of Ni/hydrotalcite, in terms of space–time yield (STY), the best synthesized catalyst is the most efficient one (STY = 137.19 mol CH4 h−1 L−1 at 300 °C) and this high efficiency is kept at low temperature (STY = 132.67 mol CH4 h−1 L−1 at 250 °C). Results show that the amount of reduced Ni, created upon the mild reduction, increases with the Ni loading and the Ni0 amount correlates with the catalytic activity. CO2 adsorption capacity remarkably increases with the Ni content but this trend does not correlate with the conversion. Surface areas, neither pore sizes, do not show a correlation with catalytic results. The most important result is the very high activity observed at temperatures below 300 °C. Characterization results indicate that the outstanding low‐temperature performance must be due to the presence of high amounts of small and reduced Ni crystallites with low interaction with the support. Developed catalysts are stable for 28 h at 300 °C.

Improved Dual Function Materials for CO2 Capture and In Situ Methanation

“…[ 33 ] The crystallite size ( τ ) was calculated using the Scherrer equation and a reported method. [ 25 ]…”

“…Layered double hydroxides (LDH) were synthesized by the co-precipitation method in accordance with previous reports. [25,29] Solution A is added dropwise to solution B with vigorous stirring, maintaining pH 9.5 AE 0.5 by adding 1 M NaOH. [30] Once the dropping ended, the mixture was stirred for an additional 4 h, for aging, and then left without stirring overnight for decantation and separation.…”

“…[33] The crystallite size (τ) was calculated using the Scherrer equation and a reported method. [25] A JEOL JSM 6490 LV equipment was used for scanning electron microscopy (SEM, DENTON VACUUM Desk IV equipment). H 2 -temperature programmed reduction (TPR) and CO 2 -temperature programmed desorption (TPD) analyses were obtained in an AutoChem II 2920 (Micromeritics Instrument Corp.), following the procedure reported elsewhere.…”

“…[39,40] The NiO phase was observed at 37.3°, 62.8°w and 79.4°, which correspond to the (111), (220), and (222) crystal faces of NiO, respectively. [25,41] Table 2 shows the morphological parameters "a" and "c" and the average Ni 0 crystallite size, calculated as described in the methodology section. Ni 0 crystallite size was determined from the XRD signal at 43.2°, [42] using the Scherrer Equation.…”

“…As an important result that could contribute to the development of better DFMs, it was recently found by our research team that some Ni‐containing oxides prepared from hydrotalcites (Ni–Mg–Al catalysts) have good activity for CO 2 methanation at low temperatures. [ 25 ] It has been also reported that Ni–Al/hydrotalcite catalysts have a higher amount of highly dispersed nickel crystallites (nanosized), and these nickel sites are more reducible than those of conventional Ni/γ–Al 2 O 3 catalysts. [ 26,27 ] These Ni–Mg–Al catalysts, synthesized from the mild‐temperature reduction with H 2 of a Ni‐hydrotalcite (without previous calcination), [ 28 ] showed remarkable low‐temperature performance in the methanation of CO 2 , and this behavior was attributed to the synthesis procedure that led to the presence of high amounts of small and reduced Ni 0 crystallites, i.e., highly dispersed, with low interaction with the support.…”