Alternate cycles of CO 2 storage and in situ hydrogenation to CH 4 on Ni–Na 2 CO 3 /Al 2 O 3 : influence of promoter addition and calcination temperature

• Published in: Sustainable energy & fuels 2021-02, Vol.5 (4), p.1194-1210
• Main Authors: Bermejo-López, Alejandro, Pereda-Ayo, Beñat, González-Marcos, José A., González-Velasco, Juan R.
• Format: Article
• Language: English
• ISSN: 2398-4902; 2398-4902
• DOI: 10.1039/D0SE01677B

Alternate cycles of CO 2 adsorption and in situ hydrogenation to CH 4 using dual function materials (DFMs) allows eliminating the intermediate and expensive CO 2 purification step. Several DFMs with composition 10% Ni–10% Na 2 CO 3 have been synthesized by wet impregnation and subsequent calcination in an extended range of temperatures. Then, the influence of the addition of low quantities (1 wt%) of promoters, such as La, Co, Fe, Ca, Ce, Ru, Pd and Mn, has been studied. All prepared samples were characterized, and the influence of calcination temperature and the nature of promoters on the catalytic behaviour has been analysed and related to the physicochemical properties of the prepared samples. A higher calcination temperature reduces the specific surface area and modifies metal–support interaction, promoting the sintering of nickel with the consequent reduction of metal dispersion; also the basicity and reducibility of nickel species are reduced. The trade-off between calcination temperature and reactivity is discovered and resolved for efficient CO 2 adsorption and in situ hydrogenation. An optimal calcination temperature of 550 °C achieved the highest production of CH 4 per cycle (177 μmol g −1 ) with high selectivity (90%). On the other hand, the addition of promoters (1 wt%) generally increases the catalytic activity without noticeable changes in the physicochemical properties of the samples, with the exception of ruthenium, which notably enhanced dispersion and reducibility. The sample 10% Ni–10% Na 2 CO 3 (1% Ru)/Al 2 O 3 boosted the production to 266 μmol g −1 of CH 4 per cycle, also maintaining higher selectivity. Ru-promoted and non-promoted samples showed stable CH 4 production during long-term experiments. However, CH 4 production was significantly reduced when oxygen was included in the CO 2 adsorption step. It was possible to partially recover the activity of the catalyst after a long regeneration period or by removing oxygen from the feed, especially for the Ru-promoted sample.