Search

Self-sustained catalytic combustion is a promising strategy to remove CO from the off-gas produced during steelmaking, where the potential catalysts are bulk copper-cerium-zirconium mixed oxides or those supported on TiO 2 or ZSM-5 substrates. In this study, the effects of the catalyst support on the CO catalytic ignition performance and reaction pathways were investigated by FTIR coupled with a novel in-situ cell, together with the state-of-the-art characterization techniques. The Infrared (IR) transmission cell equipped with a magnetically driven system, could effectively prevent overlaps between active intermediate peaks (Cu+-CO and Cu+(CO) 2) and gaseous CO peaks. The Cu+ cations located at the phase interface are the main active sites. The Cu and Ce interactions lead to the formation of solid solutions of CuCe 0.75 Zr 0.25 O δ (CuCeZr). The monocarbonyls [Cu+-CO] are the dominant species during CO oxidation, and the vacancies in the solid solutions are occupied by oxygen, accelerating the oxygen cycle. The TiO 2 or ZSM-5 supports promote copper dispersion over CuCe 0.75 Zr 0.25 O δ /TiO 2 (CuCeZr/T) and CuCe 0.75 Zr 0.25 O δ /ZSM-5 (CuCeZr/Z) catalysts, which can be attributed to their high surface areas (168.2 and 346.3 m2/g, respectively), while the Cu-Ce interactions are less relevant. Hence, CO oxidation mainly occurs at the phase interface between copper oxide and TiO 2 /ZSM-5. Dicarbonyls [Cu+(CO) 2 ] are the main intermediates for the CuCeZr/T and CuCeZr/Z catalysts, and the Cu2+ species are reduced to form dicarbonyls that also take part in the oxidation process. Although a well copper dispersion enhances the activity of individual copper sites on the CuCeZr/T and CuCeZr/Z catalysts, considering the redshift of the carbonyl bands and the increase in CO adsorption, the close interactions and high contents of Cu and Ce favor the local accumulation of heat and mass transfer over bulk CuCeZr, leading to the ignition of CO at low temperatures. [Display omitted] • CuCe 0.75 Zr 0.25 O δ and CuCe 0.75 Zr 0.25 O δ /TiO 2 and CuCe 0.75 Zr 0.25 O δ /ZSM-5 catalysts were designed. • The structure-activity relationship was obtained. • The self-sustained combustion and stability limit of CO were carried out. • The in-situ IR with a novel magnetically driven IR cell was designed and performed. • The intermediate species and reaction pathways over different catalysts were evidenced. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) and catalytic combustion (CC), which are potential technologies to promote CO→CO 2 efficient conversion and energy conservation for the steelmaking off-gas, are investigated in reaction activity, structure evolution catalysts/oxygen carriers (OCs) and energy recovery using Cu/CeO 2 materials. Activity results suggest that the rod-shaped samples with well-defined (100) crystal faces exhibit higher activity than the sphere-shaped samples with (111) crystal faces, obtaining the optimized copper content of 3 wt%. IR spectra confirmed the proposed reaction pathway that the CO adsorbed on copper sites (Cu+–CO) at the Cu–Ce interface reacts with adjacent surface lattice oxygen. The gaseous oxygen continuously migrates to the external surface of materials, thus resulting in strongly exothermic CO self-sustained combustion during CC. Such a violent reaction does not cause obvious evolution of chemical composition, crystalline phase and structure. Since the active lattice oxygen is gradually consumed but not replenished by external gaseous O 2 in time, CO combustion is not self-sustained during CLC. Therefore, the reduction cycle is no longer confined to the surface of the material but penetrates deep into its body, which accelerates Cu+ enrichment at the surface and leads to irreversible sintering and agglomeration of the material. • The activity of nanorod and nanosphere Cu/CeO 2 was compared. • CLC reaction is more exergy efficiency when burning. • The reason of catalyst deactivation in CLC was investigated. • The migration of active oxygen species in CC and CLC was compared. [ABSTRACT FROM AUTHOR]