CO2 Methanation over Hydrotalcite-Derived Nickel/Ruthenium and Supported Ruthenium Catalysts

Abstract

In this work, in-house synthesized NiMgAl, Ru/NiMgAl, and Ru/SiO 2 catalysts and a commercial ruthenium-containing material (Ru/Al 2 O 3 com. ) were tested for CO 2 methanation at 250, 300, and 350 • C (weight hourly space velocity, WHSV, of 2400 mL N,CO2 ·g −1 ·h −1 ). Materials were compared in terms of CO 2 conversion and CH 4 selectivity. Still, their performances were assessed in a short stability test (24 h) performed at 350 • C. All catalysts were characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD), N 2 physisorption at −196 • C, inductively coupled plasma optical emission spectrometry (ICP-OES), and H 2 /CO chemisorption. The catalysts with the best performance (i.e., the hydrotalcite-derived NiMgAl and Ru/NiMgAl) seem to be quite promising, even when compared with other methanation catalysts reported in the literature.Extended stability experiments (240 h of time-on-stream) were performed only over NiMgAl, which was selected based on catalytic performance and estimated price criteria. This catalyst showed some deactivation under conditions that favor CO formation (high temperature and high WHSV, i.e., 350 • C and 24,000 mL N,CO2 ·g −1 ·h −1 , respectively), but at 300 • C and low WHSV, excellent activity (ca. 90% of CO 2 conversion) and stability, with nearly complete selectivity towards methane, were obtained. This is particularly relevant whenever the destination of methane is the injection into gas grid infrastructures, where the content of species like CO should be in accordance with natural gas specifications (typically a content up to 0.5 mol % can be tolerated (e.g., [8])). Hence, highly active and methane-selective catalysts for CO 2 methanation are required. In addition, catalyst stability under dynamic operation, i.e., with the capacity to withstand temperature variations, is also quite important and particularly relevant for application in PtM processes, where the reactor is operated intermittently and whenever surplus renewable power for H 2 production is available [6].Many metals have been tested for CO 2 methanation, for instance, Ni, Ru, Rh, Pd, and Co. Among these, ruthenium and nickel catalysts supported over various materials (e.g., Al 2 O 3 , SiO 2 , TiO 2 , CeO 2 , or ZrO 2 ) stand out [9,10]. Ruthenium-based catalysts have been reported in the literature, as well as in the catalogs of some catalyst suppliers (e.g., [11,12]), to be more suited for operation at low temperatures (T<200 • C), where CO formation is inhibited due to both restricted kinetics and the endothermic nature of the parallel RWGS reaction. On the other hand, nickel-based are the most widely investigated and commercialized catalysts for CO 2 methanation due to their high activity, availability, and low cost [4]. Improvement in their catalytic performance has been reported with hydrotalcite-derived Ni catalysts [13][14][15], as well as when combining nickel with ruthenium in the same bimetallic catalyst [16]. The use of hydrotalcite-derived Ni materials has also another important feature,...

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

“…Wierzbicki et al [92,93] introduced La during the hydrotalcite preparation to further promote the support alkalinity and CO 2 chemisorption, as well as the interaction between the Ni phase and the hydrotalcite-derived support. Additionally, bimetallic catalysts were prepared by Martins et al [94], with Ru being impregnated over the initial Ni-Mg-Al hydrotalcites, while Mebrahtu et al [95] varied the amount of added Fe during the hydrotalcite synthesis. The intimate mixing of the Ni 2+ and Fe 3+ metal cations led to the formation of NiFe alloys after reduction and the alloy composition could be correlated with the catalytic performance [95].…”

Selective hydrogenation of CO2 to CH4 over two-dimensional nickel silicate molecular sieves

“…In terms of TOF, the Ni-DML-140 catalyst was superior to the other catalysts studied here, and it was also comparable to the catalysts reported in the literature (Table S2†). 40–44…”

“…In terms of TOF, the Ni-DML-140 catalyst was superior to the other catalysts studied here, and it was also comparable to the catalysts reported in the literature (Table S2 †). [40][41][42][43][44] Notably, a CH 4 selectivity greater than 90% was obtained for the catalysts showing high CO 2 conversion, such as Ni-DML-140 and Ni-DML-160. In contrast, the less active catalysts, such as Ni-DML-120 and Ni-DML-100, were more selective for CO than CH 4 .…”

Chemical engineering and environmental challenges. Cyclic adsorption/reaction technologies: Materials and process together!

“…Another option is the use of adsorption/reaction cyclic process to make Synthetic Natural Gas (SNG) from CO 2 . This is the Power-to-Gas concept; in a first step CO 2 from flue gas or other source is adsorbed over hydrotalcites (and concentrated) and in a second step hydrogen from water electrolysis powdered by renewal energy (wind) is fed and methanation reaction occurs producing SNG [38,39]. This second step is the reactive regeneration of the adsorbent (Fig.…”