Understanding the nature of single‐atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ X‐ray absorption and infrared spectroscopy to probe the edge‐site‐specific chemistry of Co−N−C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge‐hosted architecture affords single‐atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co(2−δ)+ and Co2+, in contrast to the rigid in‐plane embedded Co1−Nx counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co1−N2‐oxo with peripheral oxygen groups gives a rise to the near‐optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e− selectivity for H2O2 production.
The regeneration process of fluid catalytic cracking (FCC) units produces amounts of greenhouse gases (GHGs), including carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ). However, the flue gas GHG emission characteristics of FCC units are not well understood in China. In our work, three typical FCC units are taken as stack tests for CO 2 , N 2 O, and CH 4 emissions in the flue gas. The on-site monitoring results show that the regenerated form of the FCC unit has the greatest impact on CH 4 , and CO 2 is the primary GHG, with total emissions of >99%. Meanwhile, the spent catalysts are collected for further characterization and regeneration experiments. Results show that the coke content and composition on the spent catalysts can directly affect GHG emissions. The regeneration experiments of spent catalysts at different oxygen contents show that the main emission temperature ranges of CO 2 , N 2 O, and CH 4 are 200−600 °C, 400−600 °C, and 300−600 °C, respectively. The peaks of CO 2 and N 2 O content in regenerated flue gas increase as the O 2 content increases, while CH 4 is generated under oxygenfree conditions. The study of the GHG emission characteristics can provide theoretical support for the carbon peaking and carbon neutrality goals.
Carbon monoxide (CO) is one of the most widely spread
and enormous
pollutants in the atmosphere, and CO catalytic oxidation is the primary
method for reducing CO levels. Pd catalysts show excellent catalytic
performance in CO catalytic oxidation, yet the majority of Pd-based
catalysts are weakly resistant to sulfur. SO2, which is
particularly harmful to the catalyst, is frequently present in industrial
exhaust gases. Therefore, in this report, we have used a H2S-pretreated Pd-based catalyst for CO catalytic oxidation with outstanding
catalytic activity, sulfur resistance, and high stability. A series
of characterizations were carried out on the fresh and used catalysts,
revealing that the catalytic activity is determined by Pd0 and the sulfur resistance is dependent on PdS
x
species. The PdS
x
content is adjusted
by changing the concentration of H2S in the gas sulfidation
process. The catalytic activity of the PdS
x
catalyst is much superior to that of other Pd-based catalysts, enabling
complete oxidation of CO at around 200 °C. For the long-term
test, the PdS
x
catalyst showed good ability
and the conversion of CO was maintained at 94.93% in the presence
of 500 ppm SO2 for 300 h, indicating the excellent stability.
At last, CO catalytic oxidation and sulfur resistance mechanisms are
presented and discussed, which will provide an insight in the design
of sulfur-resistant catalysts.
Fluid Catalytic cracking (FCC) unit is one of the means to lighten heavy oil in re neries, and its regenerated ue gas is also the main source of air pollutants from re nery. However, it is not clear about the type and amount of pollutants discharged from FCC units. The emissions of regenerated pollutants in the stack ue gases of three typical FCC units in China were investigated in this study, including a partial regeneration unit without a CO boiler (U1), a partial regeneration unit with a CO boiler (U2) and a full regeneration unit (U3). Different monitoring methods were used to analyze the concentration of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ), and the results showed that Fourier Transform Infrared Spectroscopy (FTIR) monitoring results of SO 2 and NO x are approximately 10 times and 5 times larger than that of the Continuous Emission Monitoring System (CEMS) data, respectively. Also, the contents of characteristic pollutants such as NH 3 , C 6 H 6 , HCN, C 8 H 8 , C 2 H 4 , CH 4 and CO were also monitored by FTIR, and the emission factors based on coke burn-off rate and throughput were investigated. The pollutants in U1 exhibited relatively higher contents with the NH 3 , HCN and C 6 H 6 of 116.99, 71.94 and 56.41 mg/Nm 3 in ue gas, respectively. The emission of regenerated pollutants in U2 and U3 are signi cantly different from U1. Regeneration processes (including coke properties, operating modes and presence or absence of CO boilers) affected pollutants emission factors in varying degree. At last, reasonable emission factors based on the different FCC regeneration processes contributes to the prediction, assessment and control for the pollutants emission.
Understanding the nature of single-atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ Xray absorption and infrared spectroscopy to probe the edge-site-specific chemistry of CoÀ NÀ C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge-hosted architecture affords single-atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co (2À δ) + and Co 2 + , in contrast to the rigid inplane embedded Co 1 À N x counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co 1 À N 2 -oxo with peripheral oxygen groups gives a rise to the near-optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e À selectivity for H 2 O 2 production.
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