Catalytic removal of gaseous pollutant NO using CO: Catalyst structure and reaction mechanism

Carbon monoxide (CO) has recently been considered an ideal reducing agent to replace NH3 in selective catalytic reduction of NOx (NH3-SCR). This shift is particularly relevant in diesel engines, coal-fired industry, the iron and steel industry, of which generate substantial amounts of CO due to incomplete combustion. Developing high-performance catalysts remain a critical challenge for commercializing this technology. The active sites on catalyst surface play a crucial role in the various microscopic reaction steps of this reaction. This work provides a comprehensive overview and insights into the reaction mechanism of active sites on transition metal- and noble metal-based catalysts, including the types of intermediates and active sites, as well as the conversion mechanism of active molecules or atoms. In addition, the effects of factors such as O2, SO2, and alkali metals, on NO reduction by CO were discussed, and the prospects for catalyst design are proposed. It is hoped to provide theoretical guidance for the rational design of efficient CO selective catalytic denitration materials based on the structure-activity relations.

Insight into the mechanism of direct N-C coupling in selective catalytic reduction of NO by CO over Ni(111)-supported graphene

Selective catalytic reduction (SCR) of NO using CO as a reducing agent is a straightforward and promising approach to the simultaneous removal of NO and CO. Herein, a novel mechanism of N-C direct coupling of gaseous NO and CO into ONCO and subsequent hydrogenation of *ONCO to nitrogen-containing compounds over Ni(111)-supported graphene ((Gr/Ni(111)) is reported. The results indicate that Gr/Ni(111) can not only trigger direct N-C coupling of NO and CO to form ONCO with a low activation energy barrier of 0.11 eV, but also enable the key intermediate of *ONCO to be stable. The *ONCO chemisorbed on Gr/Ni(111) exhibits negative univalent [ONCO]- and is more stable than neutral ONCO. The hydrogenation pathways show that HNCO preferably forms through a kinetically favorable initial N-C coupling due to the lowest free-energy barrier of 0.18 eV, while NH2CH3 is a considerably competitive product because its free-energy barrier is only 0.20 eV higher than that of HNCO. Our results provide a fundamental insight into the novel reaction mechanism of the SCR of NO and also suggest that nickel-supported graphene is a potential and high-efficient catalyst for eliminating CO and NO harmful gases.

CuO decorated vacancy-rich CeO2 nanopencils for highly efficient catalytic NO reduction by CO at low temperature

With the rapid development of transportation and vehicles, the elimination of NO_x and CO has highly attracted public attention. In this work, vacancy-rich CeO₂ nanopencil supported CuO catalysts (CuO/CeO₂-NPC) were successfully prepared for NO reduction by CO. Importantly, CeO₂ with nanopencil-like shape (CeO₂-NPC) have been synthesis by solvothermal method for the first time. The physicochemical properties of all samples were studied in detail by combining the means of X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (H₂-TPR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ physisorption (Brunauer-Emmett-Teller), and NO and CO temperature-programmed desorption (NO-TPD and CO-TPD) techniques. Compared with CeO₂ nanorods and nanoparticles supported CuO catalysts (CuO/CeO₂-NR and CuO/CeO₂-NP), the CuO/CeO₂-NPC catalysts showed the highest catalytic activity, affording more than 90% NO conversion at 69 °C as well as excellent H₂O tolerance at 150 °C, which is superior to catalysts previously reported. Characterization results indicated that the synergistic effect between the well-dispersed CuO and the CeO₂ nanopencil support enables a favorable electron transfer between these components and enhances the density of surface oxygen vacancies and Cu⁺ species, which consequently accelerating the redox cycle. The results indicated that the morphology control of CeO₂ support could be an efficient way to evidently enhance the catalytic performance for NO + CO reaction.

Constructing a Channel to Regulate the Electron-Transfer Behavior of CO Adsorption and Light-Driven CO Reduction by H2 over CuO-ZnO

Photocatalytic conversions of C1 molecules under mild conditions have been widely researched in many fields. Adsorption of reactants at a catalyst surface is an indispensable process for C1 conversion and thus it might play a key role in reaction behavior. Herein, for a ZnO sample without photocatalytic activity for CO + H₂ reduction, CuO is introduced into ZnO to regulate the adsorption behavior of CO on the CuO-ZnO surface and then to drive the reduction of CO by H₂ under UV irradiation. The results of gas sensitivity tests and various in situ characterization methods are as expected. Specifically, surface zinc vacancies and Cu²⁺ sites at the interface of ZnO and CuO cooperate to construct a special electron-transfer channel (Zn-O-Cu-O) for CO adsorption [CO (ads)]. A new linear adsorption mode of CO at Cu²⁺ sites occurs, and this successfully changes the electron-transfer behavior of CO (ads) from donating electrons (to ZnO) to accepting electrons (from CuO-ZnO) via electron-transfer channels and d-electrons of Cu²⁺ matching. Then, CO molecules are reduced by H₂ under UV irradiation. The strategy here provides an insight into the design of highly effective catalysts as well as an in-depth understanding of the mechanism of C1 photocatalytic conversion.

Enhanced activity and sulfur resistance of Cu- and Fe-modified activated carbon for the reduction of NO by CO from regeneration gas

The reduction of NO by CO was proposed to be applied for regeneration gas to remove NOx from industrial flue gas with activated carbon purification technology.

Improved Pd/CeO2 Catalysts for Low-Temperature NO Reduction: Activation of CeO2 Lattice Oxygen by Fe Doping

Developing better three-way catalysts with improved low-temperature performance is essential for cold start emission control. Density functional theory in combination with microkinetics simulations is used to predict reactivity of CO/NO/H2 mixtures on a small Pd cluster on CeO2(111). At low temperatures, N2O formation occurs via a N2O2 dimer over metallic Pd3. Part of the N2O intermediate product re-oxidizes Pd, limiting NO conversion and requiring rich conditions to obtain high N2 selectivity. High N2 selectivity at elevated temperatures is due to N2O decomposition on oxygen vacancies. Doping CeO2 by Fe is predicted to lead to more oxygen vacancies and a higher N2 selectivity, which is validated by the lower onset of N2 formation for a Pd catalyst supported on Fe-doped CeO2 prepared by flame spray pyrolysis. Activating ceria surface oxygen by transition metal doping is a promising strategy to improve the performance of three-way catalysts.

Investigation of the NO reduction by CO reaction over oxidized and reduced NiOx/CeO2 catalysts

NO reduction by CO reaction was investigated by NiOx/CeO2 catalysts with different pretreatment conditions. Surface area, oxygen defect sites, and CeO2 crystallite size are closely related to the catalytic performance.

A first-principles understanding of the CO-assisted NO reduction on the IrRu/Al2O3 catalyst under O2-rich conditions

The IrRu alloy offered optimal energetics for NO reduction by CO. The ensemble effect plays a key role in promoting the reactivity of the IrRu alloy. Making the IrRu surface alloy is better for CO-SCR than forming an alloy over the bulk structure.

A review of the catalysts used in the reduction of NO by CO for gas purification

The reduction of NO by the CO produced by incomplete combustion in the flue gas can remove CO and NO simultaneously and economically. However, there are some problems and challenges in the industrial application which limit the application of this process. In this work, noble metal catalysts and transition metal catalysts used in the reduction of NO by CO in recent years are systematically reviewed, emphasizing the research progress on Ir-based catalysts and Cu-based catalysts with prospective applications. The effects of catalyst support, additives, pretreatment methods, and physicochemical properties of catalysts on catalytic activity are summarized. In addition, the effects of atmosphere conditions on the catalytic activity are discussed. Several kinds of reaction mechanisms are proposed for noble metal catalysts and transition metal catalysts. Ir-based catalysts have an excellent activity for NO reduction by CO in the presence of O₂. Cu-based bimetallic catalysts show better catalytic performance in the absence of O₂, in that the adsorption and dissociation of NO can occur on both oxygen vacancies and metal sites. Finally, the potential problems existing in the application of the reduction of NO by CO in industrial flue gas are analyzed and some promising solutions are put forward through this review.

Unravelling the structure sensitivity of CuO/SiO2 catalysts in the NO + CO reaction

CuO/SiO₂ catalysts with vast difference in copper dispersion were prepared by impregnation and ammonia-evaporation methods and used for exploring the structure sensitivity of CuO/SiO₂ catalysts in the NO + CO reaction.

Effect of a ZrO2 support on Cu/Fe2O3–CeO2/ZrO2 catalysts for NO removal by CO using a rotary reactor

The effect of a ZrO₂ support on the activity and adsorption behavior of Cu/Fe₂O₃–CeO₂/ZrO₂ catalysts was promoted by the oxygen vacancy.