Methanation of CO₂ over Yb-Promoted Ni/Al₂O₃ Catalysts Prepared by Solution Combustion

Abstract

Introducing a proper promoter into Ni-based catalysts for CO 2 methanation is an effective method to improve their catalytic performance. In this work, we prepare a series of Ybmodified Ni/Al 2 O 3 catalysts by a solution combustion approach and characterize them using various techniques, including nitrogen adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed hydrogen reduction (H 2 -TPR), hydrogen desorption (H 2 -TPD), carbon dioxide desorption (CO 2 -TPD), Fourier transform infrared (FTIR), and Thermogravimetric/differential thermal (TG/DTA), and test their CO 2 methanation activity in a fixed-bed reactor under conditions of 200−500 °C, 0.1−2 MPa, space velocities ranging from 7200 to 16,200 h −1 , and feed molar ratios of H 2 /CO 2 from 1 to 4. We found that Yb modification promotes the dispersion of reducible NiO on Al 2 O 3 and simultaneously leads to the creation of new Yb-involved CO 2 chemisorption sites responsible for the improved catalytic activity and stability of Ni/Al 2 O 3 catalysts for CO 2 methanation so that the Yb-modified Ni/Al 2 O 3 catalysts exhibit higher catalytic activities than Ni/Al 2 O 3 catalysts without Yb.

Combined In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy and Kinetic Studies on CO2 Methanation Reaction over Ni/Al2O3

“…The reduction of NiO after H 2 pretreatment can also be evidenced by the quasi in situ XPS analysis (Figure ). The Ni 2p 3/2 spectra of the fresh sample exhibit two peaks at 855.9 and 862.0 eV assigned to Ni 2+ species (Figure c) . After H 2 reduction at 500 °C, a new peak appears at 852.4 eV, characteristic of the Ni 0 species (Figure d) .…”

“…The Ni 2p 3/2 spectra of the fresh sample exhibit two peaks at 855.9 and 862.0 eV assigned to Ni 2+ species (Figure 1c). 17 After H 2 reduction at 500 °C, a new peak appears at 852.4 eV, characteristic of the Ni 0 species (Figure 1d). 18 It is considered that Ni 0 is the active site for CO 2 methanation, which plays an important role in dissociating hydrogen into *H and the hydrogenation of CO into CH 4 .…”