Mechanism Of Catalytic Reduction Research Articles

Promoting effects of cerium oxide on catalysts performance for selectivity catalytic oxidation of NH3 over RuOx/TiO2

Cerium oxide (CeO2) was added to modified Ru/TiO2 catalyst by a two-step impregnation method for selective catalytic oxidation of ammonia (NH3-SCO). The low-temperature NH3 oxidation activity and N2 selectivity of the 1Ru/xCe-TiO2 catalyst were investigated with the result that both SCO activity and N2 selectivity were influenced by the amount of Ce. Specifically, the presence of 5 wt% CeO2 demonstrated a great promoting effect on both parameters, reaching an NH3 conversion and N2 selectivity of 97 % and 93 % at 180 ℃, respectively. Various characterization methods indicated that the presence of CeO2 regulates the dispersion of the 1Ru/xCe-TiO2 catalysts, changes the amount, strength and ratio of strong and weak acid sites on the catalyst surface, and promotes the formation of Ru-O-Ce bonds through the interaction between Ce and Ru species, which facilitates electron transfer and oxygen vacancy formation, thereby enhancing the oxidation ability of the catalysts. Furthermore, the results of in situ diffuse reflectance infrared Fourier transform spectroscopy indicated that the NH3-SCO reaction over the 1Ru/xCe-TiO2 catalysts follows the “internal” selective catalytic reduction (i-SCR) mechanism, involving the oxidation of NH3 into nitric oxide (NO) species and the reaction of -NH2 with in situ-formed NO to form N2.

Mechanism study on CO2 hydrogenation to methanol on Cu5/TiO2 catalyst

Copper clusters supported on TiO2 have demonstrated exceptional performance in catalyzing the reduction of CO2. However, there is a lack of detailed studies on the underlying mechanism. In this study, we employ first-principles thermodynamics and kinetic calculations to unveil the catalytic reduction mechanism of CO2 to C1 product on the Cu5/TiO2 catalyst. Our calculations reveal that the interaction between the cluster and the support significantly enhances the chemical adsorption of CO2 and lowers the dissociation barrier of H2, creating favorable conditions for hydrogenation reduction of CO2. Additionally, our findings suggest that the Cu5 cluster also significantly enhances the adsorption of *CO intermediates, resulting in a preference for the RWGS pathway over the formate pathway for CO2 reduction. The rate-determining barrier for CH3OH formation is considerably lower than that for CH4 formation, indicating that Cu5/TiO2 exhibits remarkable CO2 conversion performance with nearly 100 % selectivity towards CH3OH production.

Pt/Al2O3@Ce/ZrO2-S bifunctional catalysts prepared by mechanically milling for selective catalytic oxidation of high-concentration ammonia.

The selective catalytic oxidation (SCO) is an effective method for removing slipped high-concentration ammonia from NH3-fueled engine exhaust gas. Herein a novel bifunctional catalyst was synthesized by mechanically mixing sulfated Ce/ZrO2 (Ce/ZrO2-S) with a small fraction of Pt/Al2O3 (Pt 0.1 wt.%) for SCO of NH3. As expected, the introduction of a small amount of Pt/Al2O3 significantly improved NH3 conversion ability of Ce/ZrO2-S catalysts toward low-temperature direction. When the mass ratio of Pt/Al2O3 to Ce/ZrO2-S was 7.5% (the corresponding mixed catalyst was denoted as P@CZS-7.5), T90 temperature was 312°C. More importantly, P@CZS-7.5 catalyst exhibited a much better N2 selectivity (> 96%) in a wide temperature range (320 ~ 450°C). H2-TPR results revealed that the addition of a trace amount of Pt/Al2O3 significantly led to a distinct shift of reduction temperature peak toward low-temperature direction, thereby greatly improved the low-temperature redox performance of mixed catalysts. Furthermore, NH3-TPD and BET results showed that P@CZS-7.5 catalyst exhibited a similar NH3 adsorption capacity to Ce/ZrO2-S catalyst, while the former had a relatively higher specific surface area than the latter. It was considered as a crucial factor for P@CZS-7.5 catalyst maintaining superior N2 selectivity in high-concentration NH3 (5000ppm) removal processes. In situ DRIFTS results indicated that P@CZS-7.5 catalyst followed the internal selective catalytic reduction (i-SCR) mechanism in NH3-SCO reactions.

Temperature-driven dynamic evolution process of Ag species on silver-loaded Zr0.2Sn0.8O2 catalyst for selective catalytic oxidation of ammonia

Silver-based catalysts are extensively utilized in the selective catalytic oxidation of ammonia (NH3-SCO). However, enhancing low-temperature activity often causes a decline in N2 selectivity, presenting a substantial challenge in balancing activity and N2 selectivity. In this work, we introduced zirconium into the SnO2 support, resulting in a significant enhancement of low-temperature activity by 200 °C for the Ag/Zr0.2Sn0.8O2 catalyst; yet, this also led to the formation of N2O at low temperatures and NOx at high temperatures. Characterizations such as XPS and in situ DRIFTS revealed that the dynamic changes of silver species driven by temperature had a profound impact on the reaction mechanism and guided the formation of different products. Below 200 °C, the predominance of Ag+ directed the imide mechanism, with the –HNO species being the key intermediate leading to the production of N2O. Above 300 °C, Ag0 became dominant, favoring the internal selective catalytic reduction (i-SCR) mechanism and the production of NOx. This work provides novel insights into improving N2 selectivity of Ag-based catalysts and contributes to a deeper understanding of the reaction mechanisms.

Construction of bionic sea urchin-like ZnFe2O4/Bi2S3 heterojunction for microwave-induced catalytic reduction of Cr(VI): Performance and mechanism insights

The construction of microwave-responsive catalysts with high reactivity for detoxifying heavy metal ions, particularl Cr(VI) in wastewater, poses a significant challenge. In this study, a novel microwave-responsive sea urchin-like ZnFe2O4/Bi2S3 heterojunction catalyst was designed for the rapid reduction of Cr(VI) from wastewater. Thanks to the unique “tip” structure of its surface, and its exceptional microwave absorption capabilities, the as-prepared sea urchin-like ZnFe2O4/Bi2S3 heterojunction was capable of removing 98 % pollutant from a 50 mg/L Cr(VI) solution under microwave irradiation for 40 min, even in a near-neutral aqueous environment. Importantly, this sea urchin-like ZnFe2O4/Bi2S3 heterojunction maintains efficient microwave-induced catalytic removal of Cr(VI) in complex water environments containing coexisting pollutants such as Methylene Blue (MB), Methyl Orange (MO), Crystal Violet (CV), Rhodamine B (RhB), Tetracycline (TC), Reactive Red X (RBR-X-3B), Congo Red (CR), Ketoprofen (KTP) drug, Norfloxacin (NOF) and Uranium(VI) (U(VI)). Furthermore, density functional theory (DFT) calculations reveal that the inhibited interface between ZnFe2O4 and Bi2S3 accelerates the transfer of electrons from ZnFe2O4 to Cr(VI) adsorbed on the surface of Bi2S3. Additionally, the synergistic interaction of ZnFe2O4 with Bi2S3 promotes the conversion of *Cr2O72- ions to *CrO3H3 ions and reduces the energy barrier of the rate determining hydrogenation step from −0.60 to −1.70 eV. This work serves as a reference for designing highly active microwave-responsive heterojunction catalysts, and offers theoretical guidance for a deeper understanding behind the mechanism of microwave-induced catalytic reduction of heavy metal ions.

Enhancing activity and non-deactivating stability on N-modified TiO2 catalyst for visible-light photocatalytic oxidation of ammonia at room temperature

Nitrogen modified TiO2 catalysts (N-TiO2(1)) with high photocatalytic activity and non-deactivating stability were prepared by using urea as nitrogen source. Its efficiency of photocatalytic oxidation of NH3 (NH3-PCO) remained above 80 %, peaking at 88 % at room temperature over 72 h, while N2 selectivity also improved noticeably, stabilizing at approximately 87.1 %. Conversely, the NH3 conversion on pure TiO2 plateaued at approximately 67 % within 72 h, peaking at only 72.8 %, with nitrogen selectivity not exceeding 55 %. N element was successfully doped into TiO2 lattice system in the form of O-Ti-N, which reduced the band gap energy from 3.18 eV to 3.07 eV and improved the light utilization rate. The water molecules formed during the reaction contribute to the in-situ reaction to continually generate hydroxyl radicals (·OH), thereby conferring greater reaction stability. By-products NOx- and NOx are formed during the reaction process, while NOx will be also converted to N2 by initial selective catalytic reduction (i-SCR) mechanism. These findings present a novel perspective for enhancing the stability of NH3-PCO active agents and have substantial applications within the parameters of air pollution control.

Mechanism of selective catalytic reduction on VOx/TiO2 catalyst by in situ ambient pressure X-ray photoelectron spectroscopy

Unveiling the relationship between NH3 adsorption/activation behaviors and SCR reaction mechanism is imperative for rational catalyst design, but is is still not established because of lacking methodology of in situ spectroscopies. Here, vanadia-based SCR catalysts were used to identify the electron transfer and dynamic evolutions of active sites in SCR reaction by in situ AP-XPS, Raman, and DRIFTS spectra. The activation of NH3 occurred at V5+O sites, and then they reduced to V4+OH species by proton-coupled electron transfer process at high temperature (350 °C). Reducibility of vanadium dominated the catalytic reaction and both lattice and surface oxygen can oxidize the V4+OH to fulfill redox cycles. Whereas, at low temperature (150 °C), the adsorptions of NH3 on Brønsted acid sites was the rate-determine step of NH3 activations. NO was stored as nitrate/nitrite with the help of surface chemisorbed oxygen. The NHx species reacted with adsorbed nitrite/nitrate to generate the NHxNOx intermediate that subsequently decomposed into N2 and H2O.

Low temperature NH3 selective catalytic reduction of NOx over CeOx-biochar catalyst prepared by air oxidation

A highly efficient CeOx-BC0.6 (BC: biochar. 0.6: mass ratio of Ce/(BC + Ce)) catalyst was prepared by air oxidation for low temperature NH3 selective catalytic reduction of NOx. The catalytic performance, characterization and reaction mechanism of the CeOx-BC0.6 were investigated. The results showed that NOx conversion and N2 selectivity of CeOx-BC0.6 catalyst obtained by calcining in air were above 90 % at 150–300 °C and 100,000 h−1. The surface oxygen groups, acid sites and oxygen vacancies were generated by air oxidation treatment, which promoted the adsorption and activation of reactants. NH3 and NOx were adsorbed on the catalyst surface in the form of NH4+, NH3+, nitrite and nitrate adspecies. The redox cycles of ketonic carbonyl/phenol (CO/C–OH) pairs and Ce4+/Ce3+ pairs were responsible for the activation of NH3 and NOx. NH2NO and NH4NO2 were the main active intermediates. The reaction of NH3 selective catalytic reduction of NOx over CeOx-BC0.6 mainly followed Eley-Rideal mechanism. These results will promote the understanding of mechanism of NH3 selective catalytic reduction of NOx for biochar-based catalyst prepared by air oxidation.

Direct time-resolved observation of surface-bound carbon dioxide radical anions on metallic nanocatalysts

Time-resolved identification of surface-bound intermediates on metallic nanocatalysts is imperative to develop an accurate understanding of the elementary steps of CO2 reduction. Direct observation on initial electron transfer to CO2 to form surface-bound CO2•− radicals is lacking due to the technical challenges. Here, we use picosecond pulse radiolysis to generate CO2•− via aqueous electron attachment and observe the stabilization processes toward well-defined nanoscale metallic sites. The time-resolved method combined with molecular simulations identifies surface-bound intermediates with characteristic transient absorption bands and distinct kinetics from nanosecond to the second timescale for three typical metallic nanocatalysts: Cu, Au, and Ni. The interfacial interactions are further investigated by varying the important factors, such as catalyst size and the presence of cation in the electrolyte. This work highlights fundamental ultrafast spectroscopy to clarify the critical initial step in the CO2 catalytic reduction mechanism.

Copper loading effect on active species formation over Cu/SSZ-13 catalysts for selective catalytic oxidation of high-concentration NH3

Cu/SSZ-13 catalysts not only exhibit superior SCR performance but also possess excellent selective catalytic oxidation (SCO) ability to remove NH3 escaped from engine exhaust gas fueled by NH3. To elucidate the effect of Cu loading on Cu/SSZ-13 catalysts, a series of Cu/SSZ-13 catalysts were prepared through wet impregnation method to remove high-concentration NH3 (5000 ppm). The SCO activity test results showed that when Cu loading increased from 1% to 10%, there was an obvious improvement effect on NH3 conversion performance at low temperature. Cu10/SSZ-13 catalyst reached a high NH3 conversion of 96% at 250 °C, and N2 selectivity was higher than 86% in the whole temperature range. However, when further increasing Cu loading from 10% to 20%, there was no distinctive difference in NH3 conversion and N2 selectivity. The characterization results indicated that there were abundant active species, adsorbed oxygen species, and acid sites on the surface of Cu10/SSZ-13 catalyst. The [Cu(OH)]+ and isolated Cu2+ species in zeolite channels of Cu10/SSZ-13 catalyst rather than CuO species on the surface played a key role in NH3-SCO reactions. Since 20% Cu loading would result in a significant decrease in isolated Cu2+ species, it resulted in both [Cu(OH)]+ species in zeolite channels and superfluous Cu species on zeolite surface being main active species in NH3-SCO reactions. In-situ DRIFTS experiments suggested that NH3-SCO reactions over Cu/SSZ-13 catalysts followed the internal selective catalytic reduction (i-SCR) mechanism.

An Experimental and Density Functional Theory Simulation Study of NO Reduction Mechanisms over Fe0 Supported on Graphene with and without CO.

NO reduction over highly dispersed zerovalent iron (Fe0) supported on graphene (G), with and without the presence of CO in the reacting stream, was systematically studied using a fixed-bed reactor, and the reaction mechanism was examined with the aid of in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The in situ FTIR results showed that NO adsorbed on the Fe0 site is reduced to form active surface oxygen species (O*), which is then reduced by carbon in graphene to form CO2. The presence of CO in the reacting stream helps to reduce the oxidized Fe(O) sites to regenerate Fe0 sites, making NO reduction easier. It was revealed that NO and CO2 are easily adsorbed on the active surface oxygen species (O*) to form nitrate and carbonate, inhibiting their reduction by CO and deactivating the catalyst. The DFT calculations results suggest that the role of Fe is to reduce the energy barrier of the NO adsorption and decomposition, which controls the formation of active surface oxygen species and N2. The combined FTIR and DFT results offer new insights into the possible mechanism of catalytic NO reduction over graphene loaded with Fe, with and without CO.

Reasonable design of Sm-modified Cu-based catalyst for NH3-SCO: Role of the amide intermediates

The selective catalytic oxidation of ammonia (NH3-SCO) is currently the most effective method used to eliminate NH3. However, one of the major challenges for NH3-SCO is the development of catalyst capable of completely converting NH3 into harmless N2 and water vapor. In this paper, a high N2 selective catalyst prepared by the sol-gel method using TiO2 as the support, Cu as the active species, and Sm as the auxiliary agent is presented. Compared to traditional Cu/TiO2 catalyst, the 4SmCu/TiO2 catalyst has higher catalytic activity and N2 selectivity at low temperatures. The NH3 conversion can reach 100%, and the selectivity of N2 can be maintained at 100% at 275 °C. The excellent catalytic activity is attributed to the highly dispersed active species, abundant Lewis acid sites (LASs), and the generation of large amounts of surface-adsorbed oxygen. In addition, doping Sm species will cause TiO2 lattice distortion, and at the same time load the distorted TiO2 with more active material. Moreover, in-situ DRIFTS analysis suggests that both the 4SmCu/TiO2 and Cu/TiO2 catalysts follow the "internal" selective catalytic reduction (iSCR) mechanism during NH3-SCO reactions. The 4SmCu/TiO2 catalyst generates more amides (-NH2), which reduces the non-selective oxidation of the catalysts and promotes the formation of N2. This provides a new idea and method for the selective catalytic oxidation of NH3 to N2 and water vapor using Cu-based catalysts.

Low-temperature CO selective catalytic reduction denitrification and sulfuric acid regeneration mechanism of Cu-Ce/AC catalyst poisoned with zinc salt

To explore Cu–Ce/activated carbon (AC) catalyst poisoned of with zinc salt and its mechanism of low-temperature CO selective catalytic reduction (CO-SCR) denitrification following sulfuric acid regeneration, this paper uses ZnCl2 and ZnSO4 to poison Cu–Ce/AC catalyst and H2SO4 pickling to regenerate the poisoned catalyst. Not only the catalyst denitrification activity was investigated but also the surface morphology, pore structure, variation of active component phases and elemental valence, surface functional groups, reduction characteristics and adsorption mechanism of catalyst before and after regeneration were systematically characterized. The low-temperature CO-SCR denitrification mechanism of the poisoned Cu–Ce/AC catalyst was revealed. After being poisoned with zinc salt, the oxide on the catalyst surface aggregated, causing the blockage of the pore, thereby inhibiting the adsorption capacity of the reaction gas and the synergistic reaction between Cu-Ce. Moreover, zinc salt not only occupies the active site, but also destroys the -C=O and –OH oxygen-containing functional groups. This not only reduces the chemically adsorbed oxygen (Oβ) and oxygen vacancy but also leads to the reduction of Cu+–CO species, the reduction of catalyst redox capacity, and the reduction of NO conversion rate. The regeneration mechanism of the sulfuric acid method was as follows. First, the solid particles deposited on the catalyst surface are removed, thereby restoring its specific surface area and pore structure, and increasing the adsorption area of reaction gas. Additionally, the content of Cu and Ce active components was increased, which promoted the synergistic reaction, and the content of Cu+–CO species, oxygen vacancy, and Oβ was increased, resulting in enhanced redox capacity. Finally, sulfuric acid impregnation generated S2O82− groups, which sulfated the surface of the catalyst, and its S=O reacted with Zn to form S–O–S, which prevented zinc salt from destroying the oxygen-containing functional groups and improved the reducing capacity and CO adsorption capacity of the catalyst, thereby restoring the denitrification activity of the catalyst.

Fabrication of highly dispersed carbon doped Cu-based oxides as superior selective catalytic oxidation of ammonia catalysts via employing citric acid-modified carbon nanotubes doping CuAl-LDHs

In this work, the CuAl-LDO/c-CNTs catalyst was fabricated via in situ oriented assembly of layered-double hydroxides (LDHs) and citric acid-modified carbon nanotubes (c-CNTs) followed by annealing treatment, and evaluated in the selective catalytic oxidation (SCO) of NH3 to N2. The CuAl-LDO/c-CNTs catalyst presented better catalytic performance (98% NH3 conversion with nearly 90% N2 selectivity at 513 K) than other catalysts, such as CuAlOx/CNTs, CuAlOx/c-CNTs and CuAl-LDO/CNTs. Multiple characterizations were utilized to analyze the difference of physicochemical properties among four catalysts. XRD, TEM and XPS analyses manifested that CuO and Cu2O nanoparticles dispersed well on the surface of the CuAl-LDO/c-CNTs catalyst. Compared with other catalysts, larger specific surface area and better dispersion of CuAl-LDO/c-CNTs catalyst were conducive to the exposure of more active sites, thus improving the redox capacity of the active site and NH3 adsorption capacity. In-situ DRIFTS results revealed that the internal selective catalytic reduction (iSCR) mechanism was found over CuAl-LDO/c-CNTs catalyst.

Insight into the Mechanism of Selective Catalytic Reduction of NO by CO over a Bimetallic IrRu/ZSM-5 Catalyst in the Absence/Presence of O2 by Isotopic C13O Tracing Methods.

The development of efficient catalysts for the selective catalytic reduction of NO by CO (CO-SCR) in the presence of O2 is highly desirable for controlling the emission of toxic gases from tailpipes. Here, a bimetallic IrRu/ZSM-5 catalyst was prepared for the selective catalytic reduction of NO by CO in the presence of O2 (5%) for the low-temperature treatment of exhaust gas. IrRu/ZSM-5 afforded 90% NOx conversion in the range of 225-250 °C and maintained 90% NOx conversion after 12 h of reaction. Ru addition inhibited agglomeration of the Ir particles during the reduction process and provided more active sites for NO adsorption. Isotopic C13O tracing and in situ diffuse reflectance infrared Fourier-transform spectroscopy experiments were used to elucidate the CO-SCR mechanism in the absence or presence of O2. NCO could easily form on the surface of catalysts in the absence of O2, whereas NCO formation has been inhibited owing to the quick consumption of CO in the presence of O2. Moreover, some byproducts such as N2O and NO2 are generated in the presence of O2. Finally, a possible mechanism for CO-SCR under different conditions was proposed based on in situ experiments and physicochemical analyses.

Synergistic effect of silver NPs immobilized on Fe3O4@L-proline magnetic nanocomposite toward the photocatalytic degradation of Victoria blue and reduction of organic pollutants.

The surface of magnetite (Fe3O4) nanoparticles was subject to modification through the incorporation of L-proline (LP) by simple co-precipitation method in which silver nanoparticles were deposited by in situ method, thereby yielding the Fe3O4@LP-Ag nanocatalyst. The fabricated nanocatalyst was characterized using an array of techniques including Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET), and UV-Vis spectroscopy. The results evince that the immobilization of LP on the Fe3O4 magnetic support facilitated the dispersion and stabilization of Ag NPs. The SPION@LP-Ag nanophotocatalyst exhibited exceptional catalytic efficiency facilitating the reduction of MO, MB, p-NP, p-NA, NB, and CR in the presence of NaBH4. The rate constants obtained from the pseudo-first-order equation were 0.78, 0.41, 0.34, 0.27, 0.45, 0.44, and 0.34 min-1 for CR, p-NP, NB, MB, MO, and p-NA, respectively. Additionally, the Langmuir-Hinshelwood model was deemed the most probable mechanism for catalytic reduction. The novelty of this study lies in the use of L-proline immobilized on Fe3O4 MNPs as a stabilizing agent for the in-situ deposition of silver nanoparticles, resulting in the synthesis of Fe3O4@LP-Ag nanocatalyst. This nanocatalyst exhibits high catalytic efficacy for the reduction of multiple organic pollutants and azo dyes, which can be attributed to the synergistic effects between the magnetic support and the catalytic activity of the silver nanoparticles. The easy recyclability and low cost of the Fe3O4@LP-Ag nanocatalyst further enhance its potential application in environmental remediation.

Reaction mechanism of selective catalytic reduction of NO with NH3 on Fe3O4 (1 1 1) surface: Experimental and DFT studies

Iron-based catalysts have vast potential for application prospect in selective catalytic reduction of NOx with NH3 (NH3-SCR). These catalysts offer excellent SCR activity at medium and high temperatures, N2 selectivity and environmental performance. Among these catalysts, Fe3O4 catalyst is highly active and significant in the denitration reaction due to the presence of both ferrous and ferric ions. This study utilized density functional theory (DFT) in combination with experimental measurements to investigate the reaction pathway of NH3-SCR on the Fe3O4(111) surface. The research found that the surface was favorable for the adsorption of NO molecules and followed the NO activation mechanism. Upon activation of NO at the Feoct site, it reacted with NH3 to form NH2NO, This compound then underwent decomposition into N2 and H2O. The presence of O2 on the catalyst facilitated the surface dehydrogenation reaction and completed the SCR cycle reaction. Based on the DFT results, the formation of NH2NO intermediate was the rate-determining step of SCR reaction. The Fe3O4(111) surface followed the L-H mechanism, which was in line with the experimental results. This study provided novel insights into the SCR reaction process and can be useful in developing new iron-based SCR catalysts.

Unraveling the Lattice O Assisted Internal Selective Catalytic Reduction Mechanism on High N2 Selectivity of CuOx/PtCu Catalysts in NH3-SCO

Supported Pt catalysts suffer from low reaction selectivity (<65% at 100% conversion) in the selective catalytic oxidation of ammonia (NH3-SCO) because of their intrinsic over-oxidation tendencies. Herein, a strategy based on facilitating byproduct NOx reduction to N2 is demonstrated at CuOx/PtCu catalysts, aiming to tackle the low selectivity challenge. This PtCu alloy sample with a CuOx-rich surface displays an N2 selectivity of 95%, while its turnover frequencies are the highest among reported supported Pt-based catalysts. The enhanced reaction activities and N2 selectivities are primarily attributed to the Pt-Cuδ+ dual-site synergies at the CuOx/PtCu interface, in which dual sites exhibit distinct NH3 adsorption, activation, and dehydrogenation behaviors. The Olat assisted internal selective catalytic reduction mechanism at CuOx/PtCu with N2O22– as the central intermediates is proposed. Density functional theory calculation and temperature-programmed surface reaction measurements show that the N–O bond in N2O22– tends to break simultaneously with the assistance of Ov in CuOx followed by the easy transition from N2O22– to N2, which serve as the origin of the high selectivity.

Study on the mechanism of selective catalytic reduction with propylene (C3H6-SCR) on the MnOx-based catalysts by a doping experiment and DFT+U calculation

For a long time, the research of the C3H6-SCR reaction relied only on experimental techniques, which limited the recognition of the mechanism for this process. Herein, we systematically calculated the adsorption characteristics, electronic structure, oxidation pathways, and reaction pathways of the C3H6-SCR procedure by density functional theory (DFT) based on a representative doping model. DFT calculations show that the C3H6 oxidation with NO to CH3NO2/CH3CN is more favorable to achieve energetically than CH3NO/CH3NCO, while the NO2 is a better oxidant than O2 and NO for the C3H6 oxidation at low temperatures. The excellent correlation between temperature programmed experiment and the C3H6-SCR reaction path barrier can reasonably conclude that the first step oxidation of C3H6 and the formation of amino intermediates(−NH2) are the keys to the low-temperature activity of C3H6-SCR. Besides, the stronger charge non-localization on the surface with lanthanum doping demonstrated by XPS could be responsible for the enhanced oxidation of the active sites, hence promoting NO to NO2. The study shed more light on the C3H6-SCR reaction mechanism at the molecular level and expects to contribute to the development of low-temperature C3H6-SCR.

A rational construction of Pt@Cu-ZSM-5@CuOx catalyst with detached multi-functional Pt and Cu sites for high-performance acetonitrile decomposition

Pt@Cu-ZSM-5@CuOx catalyst was constructed for the catalytic oxidation of acetonitrile (AN), which achieved a complete mineralization rate and more than 95 % N2 selectivity within 300–450 °C. Characterization results revealed that the satisfactory synergistic action of hydrolysis and oxidation pathways was well achieved. The NOx release from CN oxidation reaction on out-layer CuOx species and NHx species over-oxidation over Pt sites could be eliminated by NH3 from CN hydrolysis reaction on Cu ions via internal selective catalytic reduction mechanism. The deep oxidation of carbon-containing intermediates (such as CO etc.) during CN decomposition over Cu species effectively occurred over Pt site. The encapsulation of Pt inner ZSM-5 zeolite not only strengthened low-temperature mineralization rate compared to Cu/ZSM-5 sample, but also inhibited NOx release caused by over-oxidation of AN at an elevated temperature with co-impregnation of Pt species over Cu/ZSM-5. This work provided a viable strategy for designing catalysts to effective abatement of NVOCs.