Unravelling the synergistic effects in GdCe composite oxides supported biochar catalysts for formaldehyde elimination: Elevated performance and SO2 toleration

Abstract

A chain of GdCe oxides boosted biochars derived from maize straw and sewage sludge (Gd_yCe_1-y/MPBs) were fabricated for formaldehyde (HCHO) catalytic decomposition. The ingenerate relationship between the abatement performance and corresponding structural feature was comprehensively evaluated by XPS, in situ DRIFTS, BET, XRD, SEM and H₂-TPR. Meanwhile, 10%Gd_0.25Ce_0.75/MPB exhibited excellent performance, favorable SO₂ and moisture toleration over a broad temperature range from 160 to 320 ℃, where it achieved 96.8% removal efficiency with 90.5 % selectivity at 200 ℃. The single or united effects of O₂, SO₂, H₂O on HCHO abatement over 10 %Gd_0.25Ce_0.75/MPB were tested, and the findings demonstrated that the suppressive effects of SO₂ and H₂O outweighed the promoting influence of O₂ within a specific range. Gd and Ce co-modified MPB revealed superior HCHO removal capability in contrast to that of Gd or Ce severally modified MPB, ascribing to the synergistic effect of GdO_x and CeO_x and benefitting from the augmentation of surface area and total pore volume, the aggrandizement of surface active oxygen species, the promotion of redox ability and the inhibition crystallization of CeO_x. According to in situ DRIFTS, a series of intermediates including formate species and dioxymethylene (DOM) were produced, which would eventually decompose into H₂O and CO₂. In addition, the mass transfer and diffusion of the reactants along with the accessibility of the catalytic sites were enlarged by the hierarchical porous structure of the support, which were also answerable for its distinguished catalytic performance. Furthermore, 10%Gd_0.25Ce_0.75/MPB possessed remarkable potential for industrial applications.