Boosting Ni Dispersion on Zeolite-Supported Catalysts for CO₂ Methanation: The Influence of the Impregnation Solvent

Abstract

In this work, an enhancement of Ni0 particle dispersion over zeolite-supported catalysts was intended by tuning the impregnation solvent. For this purpose, a series of 15 wt % Ni catalysts supported over a Cs-USY zeolite were prepared by incipient wetness impregnation using water, ethanol, methanol, 2-propanol, acetone, or ethylene glycol as solvents. Samples were characterized by TGA, N2 adsorption, XRD, DRS UV–Vis, H2-TPR, CO2-TPD, and TEM and catalytically tested at atmospheric pressure under CO2 methanation conditions (86,100 mL gcat –1 h–1, P CO2 = 0.16 bar, H2/CO2 = 4:1). The use of organic solvents rather than water increased the number of weak and medium basic sites, while 2-propanol and ethylene glycol promoted metal–support interactions. The average Ni0 particle sizes after reduction at 470 °C were significantly different for all the studied solvents, ranging from 13 to 34 nm. Despite the beneficial properties exhibited by the catalyst prepared using ethylene glycol concerning metal particle dimensions and the number of weak and medium basic sites, 2-propanol allowed the highest CO2 conversion and CH4 selectivity (64 and 95%, respectively, at 350 °C), probably because of the partial damage of the zeolite structure observed when ethylene glycol was used. Materials prepared within this work were finally compared with other Ni-based catalysts from the literature, assessing the corresponding catalytic activity from CH4 production rates. Their performances were shown to be similar to or higher than those of the literature materials, thus confirming the relevance of these Ni/zeolite catalytic systems and motivating further developments towards this reaction.

Promising Catalytic Systems for CO2 Hydrogenation into CH4: A Review of Recent Studies

“…Later, Graça et al [184] reported Ni/USY catalysts and evaluated the effects of the Ni incorporation method (ion exchange or impregnation) and Ni loading, with 15 wt% found to be the best compromise. The same authors [188,189] reported that the chosen calcination and reduction temperatures as well as the impregnation solvent can be crucial in these materials. Bacariza et al evaluated the effects of the compensating cation nature [190], Si/Al ratio [174] and zeolite framework type [175] in the performances of Ni-based zeolites.…”

On the Effect of Cobalt Promotion over Ni/CeO2 Catalyst for CO2 Thermal and Plasma Assisted Methanation

“…As observed, a mass variation process was observed below 400 °C in the catalysts, corresponding to the loss of adsorbed water in the samples. On the other hand, at higher temperatures (>600 °C), where coke should be decomposed, the mass loss is negligible, indicating that no carbonaceous species were deposited in the catalysts during the tests [47]. Furthermore, stability tests were performed for the studied samples, being the results presented in Figure 8.…”

“…The step time and step size were 0.5 s and 0.03 • , respectively. CeO 2 , NiO and Ni 0 average crystallite sizes were calculated in applying the Scherrer equation [47]. For this purpose, the considered diffraction lines were: 28.6, 33.1, 47.5 and 56.4 • for CeO 2 ; 37.3 • and 43.3 • for NiO; and 44.5 and 52.1 • for Ni 0 .…”

“…High-Resolution TEM was performed using an JEOL JEM-2010 equipment with EDS to characterize the deposited carbon and to obtain a precise analysis of the planes registered at the nanometer scale (JEOL, Gmbh, Freising, Germany). The specimens were prepared by dropwise addition of a colloidal solution in ethanol onto a copper grid covered with amorphous carbon film [47].…”

“…Finally, TGA analysis were carried out using a Setsys Evolution TGA (Setaram instruments, SPECANALITICA LDA, Cracavelos, Portugal). Experiments were carried out for spent catalysts using a mass of 20 mg and heating the samples from 20 to 800 • C (heating rate = 10 • C/min) under air flow [47].…”