Ni–Al layered double hydroxides as catalyst precursors for CO2 removal by methanation

The effect of nickel content on the structure and activity of co-precipitated Ni–Al layered double hydroxides (LDHs) as catalyst precursors for CO 2 removal by methanation was studied by variation of the Ni 2+ /Al 3+ molar ratio (Ni 2+ /Al 3+ = 3.0, 1.5 and 0.5), and of the reduction and reaction temperatures as well as of the space velocities. Powder X-ray diffraction (PXRD), H 2 chemisorption, and temperature programmed reduction (TPR) techniques were applied for physicochemical characterization of the samples. It was specified that the nano-scaled dimensions of the as-synthesized samples also generate nano-metrical metallic nickel particles (PXRD). The existence of readily and hardly reducible Ni 2+ –O species in the studied samples (TPR), affects catalytic performance. The studied catalysts hydrogenate CO 2 effectively to residual concentrations of the latter in the range of 0–10 ppm at reaction temperatures from 400 to 220 °C and space velocities between 22,000 and 3000 h −1 . The variation of the CO 2 methanation activity with the changes of space velocities depends on the nickel content, and reduction and reaction temperatures. After reduction at 400 and 450 °C, a sample of Ni 2+ /Al 3+ = 3.0 has demonstrated the highest conversion degree at all the reaction temperatures and space velocities, while a catalyst of Ni 2+ /Al 3+ = 0.5 dominated in the methanation activity after reduction within 530–600 °C. The Ni 2+ /Al 3+ = 1.5 catalyst data take intermediate position between Ni 2+ /Al 3+ = 3.0 and Ni 2+ /Al 3+ = 0.5 often closer to Ni 2+ /Al 3+ = 3.0 ones. The studied Ni–Al LDH systems are found to be promising catalyst precursors for fine CO 2 removal from hydrogen-rich gas streams through the methanation reaction, depending on the technological regime of catalyst activation.