Although substantial advances have been made in a few reactions of industrial significance over single-atom catalysts (SACs), the origin of the superior catalytic performance, the nature of the active sites, and the reaction pathways are still the subject of debate. Even for CO oxidation over SACs on nonreducible substrates, the understanding is limited. We investigated the performance of Pd atoms monodispersed on graphene (PdGr) in CO oxidation. Combining firstprinciples-based thermodynamics calculations and microkinetics modeling, we showed that the positively charged PdGr can exhibit a rather high low-temperature activity in CO oxidation. Under reaction conditions, the Pd atom binds strongly with O 2 , acting as the reactive species to convert CO. A comparison of the conversion rates of steps along different potential reaction pathways provides direct evidence that CO oxidation mainly proceeds through revised Langmuir−Hinshelwood pathways, and the dissociation of the peroxide intermediate (O−O−CO) is the ratelimiting step. The predicted catalytic performance was attributed to the specific electronic structure of PdGr with the positively charged Pd on graphene monovacancy exposing sp-type frontier states. We expect these findings to help in understanding the performance of SACs and to guide the design and fabrication of SACs with superior catalytic performance.

Catalytic semireduction of internal alkynes to alkenes is very important for organic synthesis. Although great success has been achieved in this area, switchable Z/E stereoselectivity based on a single catalyst for the semireduction of internal alkynes is a longstanding challenge due to the multi-chemo- and stereoselectivity, especially based on less-expensive earth-abundant metals. Herein, we describe a switchable semireduction of alkynes to (Z)- or (E)-alkenes catalyzed by a dinuclear cobalt complex supported by a macrocyclic bis pyridyl diimine (PDI) ligand. It was found that cis-reduction of the alkyne occurs first and the Z–E alkene stereoisomerization process is formally controlled by the amount of H2O, since the concentration of H2O may influence the catalytic activity of the catalyst for isomerization. Therefore, this protocol provides a facile way to switch to either the (Z)- or (E)-olefin isomer in a single transformation by adjusting the amount of water.

No abstract

The lack of efficient catalysts with a wide working temperature window and vital O2 and SO2 resistance for selective catalytic reduction of NO by CO (CO‐SCR) largely hinders its implementation. Here, a novel Ir‐based catalyst with only 1 wt% Ir loading is reported for efficient CO‐SCR. In this catalyst, contiguous Ir atoms are isolated into single atoms, and Ir–W intermetallic nanoparticles are formed, which are supported on ordered mesoporous SiO2 (KIT‐6). Notably, this catalyst enables complete NO conversion to N2 at 250 °C in the presence of 1% O2 and has a wide temperature window (250–400 °C), outperforming the comparison samples with Ir isolated‐single‐atomic‐sites and Ir nanoparticles, respectively. Also, it possesses a high SO2 tolerance. Both experimental results and theoretical calculations reveal that single Ir atoms are negatively charged, dramatically enhancing the NO dissociation, while the Ir–W intermetallic nanoparticles accelerate the reduction of the N2O and NO2 intermediates by CO.

Fe is not only the most abundant metal on the planet, but also the key component of many enzymes in organisms that are capable to catalyze many chemical conversions. Mono-dispersed...

We compared the electronic structure and CO oxidation mechanisms over Pt atoms immobilized by both B‐vacancies and N‐vacancies on gas‐exfoliated hexagonal boron nitride. We showed that chemical bonds are formed between the B atoms associated with dangling bonds around the vacancies and Pt atoms. These bonds not only alter the thermodynamics and kinetics for the aggregation and effectively immobilize Pt atoms, but also significantly change the composition and energetic distribution of the electronic states of the composites to circumvent CO poisoning and to favour coadsorption of CO and O2, which further regulates the reactions to proceed through a Langmuir‐Hinshelwood mechanism. The CO oxidation over Pt atoms immobilized at N‐vacancies involves formation of an intermediate with –C(O)‐O−O‐ bonded to Pt, the generation of CO2 by peroxo O−O bond scission and the reduction of the remnant oxygen, and the calculated energy barriers are 0.49, 0.23 and 0.18 eV, respectively. Such small energy barriers are comparable to those over Pt atoms trapped at B‐vacancies, showing the effectiveness of Pt/hexagonal boron nitride atomic composites as catalysts for CO oxidation. These findings also suggest the feasibility of regulating the reaction pathways over single atom catalysts via interfacial engineering.

Compared to other Fen (n > 2) clusters, Fe2 cluster catalysts combined with vicinal nonmetallic sites are expected to be an ideal catalyst for ammonia synthesis with a lower N–H formation (0.47 eV) and N–N dissociation (0.50 eV) energy barrier at the same time.

No abstract