Metal hydroxide assisted integrated direct air capture and conversion to methane with Ni/Al₂O₃catalysts

Abstract

An innovative integrated route for CO2 capture and conversion to methane relying on inexpensive metal hydroxides and nickel-based catalysts is presented.

CO2 Capture and Direct Air CO2 Capture Followed by Integrated Conversion to Methane Assisted by Metal Hydroxides and a Ru/Al2O3 Catalyst

“…In a previous report, with a 25 %Ni/Al 2 O 3 catalyst, temperature played a significant role as the catalysis was greatly hindered at temperatures below 225 °C. [37] With the 5 %Ru/Al 2 O 3 catalyst in the present study the difference in yield between 200 °C and 225 °C was rather minute (Figure 3a). 200 °C produced 19 % methane with a productivity of 101.6 g methane • h À 1 • kg cat À 1 .…”

“…Metal hydroxide salts have been shown to be efficient bases for the capture of CO 2 from the atmosphere. [21,37,65,66] Thus, we performed an air capture with 10 mmol of potassium hydroxide in water. The air capture produced 5 mmol of K 2 CO 3 as shown in the 13 C NMR spectrum in Figure S13.…”

“…[33][34][35][36] Metal hydroxide salts were reported as well for the capture and conversion of CO 2 . [23,37] However, in organic solvents hydroxide bases can interact with the solvent and lead to degradation of the base over the course of the reaction, limiting their applications in these organic solvents. [21] One avenue to avoid the need for a solvent with heterogeneous catalysts is to combine the active metal, such as ruthenium or nickel, with an alkali or alkaline earth metal, such as potassium or calcium, that can capture CO 2 for further reactions.…”

“…The conversion of carbonate salts to methane has previously been reported utilizing a 25 %Ni/Al 2 O 3 catalyst, albeit the productivity numbers associated to the reaction were rather low at 12.3 g methane • h À 1 • kg cat À 1 partially due to the long reaction time of 48 hours. [37] Heterogeneous catalysts based on ruthenium have also been shown to convert CO 2 and other carbon sources to methane. [22,[50][51][52][53][54][55] In general, these ruthenium based catalysts are able to perform the reactions at a faster rate than the nickel based ones.…”

Phosphate assisted integrated carbon dioxide capture and conversion to methane

“…Prakash et al has recently shown that both sodium carbonate, sodium bicarbonate as well as other alkali metal carbonates in aqueous solution could be hydrogenated to methane using a nickel-based catalyst (25% Ni/Al 2 O 3 ). 34 Following this report, the same catalyst was initially used to test the conversion of carbon dioxide captured with trisodium phosphate to methane at 200 °C under a hydrogen pressure of 50 bar. This experiment led to a poor methane yield of only 2.6% in 6 hours (Table 1), which was likely the result of phosphorous compounds acting as ligand and binding to the nickel-based catalyst, inhibiting its reactivity (Fig.…”