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Abstract: Zirconium doped Cu/ZSM-5 catalysts were prepared and characterized in this investigation. Catalytic activity during soot combustion was determined in both O2/He and NO/O2/He atmospheres by temperature-programmed oxidation. The use of zirconium reduces the temperature of maximum soot oxidation rate by 229°C in O2/He atmosphere and 270°C in NO/O2/He atmosphere. The promoting effect of zirconium is discussed in terms of surface dispersion, enrichment of active components, and creation of oxygen vacancies where molecular oxygen or NO x is adsorbed forming basic surface oxygen species active for soot oxidation. The NO2 formed at the copper–zirconium interface sites leads to the ignition temperature being significantly decreased to 93°C, which is inside the exhaust temperature range of diesel engines. To understand the combustion reaction kinetics, the activation energy and reaction order of soot combustion were evaluated. According to the Redhead method, the activation energy for non-catalyzed reaction is 164kJ/mol under the O2/He atmosphere. For the Cu/ZSM-5 and Cu–Zr/ZSM-5, the activation energies under the O2/He atmosphere (134–151kJ/mol) are slightly higher than those under the NO/O2/He atmosphere (128–135kJ/mol). The Freeman–Carroll method is suitable to describe the soot combustion in the NO/O2/He atmosphere, with the activation energies for the catalysts in the range of 97–112kJ/mol and the average value of reaction order equal to 1.36. [Copyright &y& Elsevier]

[Display omitted] • The L-H mechanism dominates the low-temperature induction stage. • Coexistence of M−K and L-H mechanisms in ammonia catalytic combustion. • (M−K) /(L-H) = 0.427 (Induction stage) and 0.627 (continuous combustion stage). • The NH and NH 2 are the key species for the two stages of N 2 production (i-SCR). • The CuO-CeO 2 achieves self-sustained catalytic combustion at NH 3 = 14%. Carbon-free hydrogen-rich ammonia (NH 3) is a potential next energy generation source, where a high ignition point and high nitric oxide contents, thereby limiting further development. This study aims to investigate the mechanism evolution during the catalytic ignition process of high NH 3 concentration over copper-cerium catalyst to address the demerits of flame combustion. The phase composition, elemental valence, and active species of the copper-cerium oxide (CuO-CeO 2) catalyst are investigated using various characterization techniques. The results indicated that Cu species are mainly present in copper-cerium solid solutions and highly dispersed CuO clusters, providing sufficient Cu sites to adsorb NH 3 and abundant reactive lattice oxygen. The catalytic ignition triggered a kinetic transition from low-rate to high-rate steady-state. During the induction process, the predominance of the L-H mechanism is implied by the kinetic modeling and transient experiments (low-rate induced phase). Combined with IR spectroscopy and isotope (18O 2)-transient response study, the results indicated that adsorbed NH 3 reacted with surface adsorbed oxygen, simultaneously pulling out lattice oxygen to react with adsorbed NH 3 , confirming the coexistence of L-H and M−K mechanism over CuO-CeO 2. The L-H mechanism (18O, contribution of adsorbed oxygen) plays a relatively dominant role in the induction stage, while the involvement of the M−K mechanism (16O, contribution of lattice oxygen) is significantly increased in the sustained combustion stage. At both stages, NH and NH 2 served as critical species for N 2 generation (i-SCR), respectively, playing an important role in N 2 selectivity. Moreover, in the self-sustained combustion stage for CuO-CeO 2 (14%NH 3), the rapid gas diffusion and mass transfer facilitated the adsorption and activation of NH 3. These results are envisaged to provide theoretical support for the handling and application of high concentrations of NH 3. [ABSTRACT FROM AUTHOR]

Catalytic combustion (CC) and chemical looping combustion (CLC) are promising technologies for energy saving and emission reduction of CO 2 in treatment of steelmaking off-gas. This work firstly reports and compares the evolution behavior and quantitative reaction mechanisms of cube Cu 2 O model catalyst for CC and CLC reactions. The Cu 2 O-CC exhibited the higher activity and stability than Cu 2 O-CLC. The typical characterization results suggested that the only surface unstable Cu 2 O was oxidized to CuO, and the excellent synergistic effect of metal-oxide interface (100) between Cu+/Cu2+ and active lattice oxygen species for Cu 2 O-CC reaction. But, for CLC reaction, Cu 2 O structure was collapsed, which caused the agglomeration of CuO x species and gradual decrease of reaction stability. Three different active oxygen species (surface cycle lattice oxygen, bulk lattice oxygen, and adsorbed oxygen) and the detailed reaction pathways were proposed by the in situ IR spectroscopy, isotopic (18O 2) transient exchange experiments and DFT simulation. The intrinsic activity of surface cycle lattice oxygen was higher in terms of TOF (13.5 × 10−3 s−1) and facile formation of C16O18O on the cubic interface of Cu 2 O-CC through adsorbed CO during CC process. The contribution degrees of Mars-van-Krevelen (M-K) and Langmuir–Hinshelwood (L-H) mechanisms for CC and CLC reactions were 76.6% and 23.4% for CC, and 89.7% and 10.3% for CLC on Cu 2 O catalyst, respectively. [Display omitted] • The cube Cu 2 O model catalyst was well prepared by liquid-phase reduction method. • The detailed evolution behavior and structure-activity relationship of cube Cu 2 O was carried out for CC and CLC reactions. • The roles of three different active oxygen species in CC and CLC reactions were clearly distinguished. • The contribution degrees of Mars-van-Krevelen and Langmuir–Hinshelwood mechanisms for CC and CLC reaction were proposed. [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]