Catalytic Activity For NO Reduction Research Articles

Selective Formation of Cu Active Sites with Different Coordination States on Pseudospinel CuAl2O4 and Their NO Reduction Catalysis.

In the spinel framework, copper (Cu) in two distinct coordination states exhibits catalytic activity for NO reduction through different mechanisms. However, detailed exploration of their respective catalytic properties, such as the redox behavior of Cu and substrate molecule adsorption, has been challenging due to difficulties in their separate formation. In this study, we present the controlled formation of pseudospinel CuAl2O4, containing exclusively tetrahedrally or octahedrally coordinated Cu, achieved by manipulating aging temperature and O2 concentration. Through these materials, we observed that in the CO-NO reaction, the step primarily determining the rate differs: NO reduction dominates with octahedrally coordinated Cu, whereas carbon monoxide (CO) oxidation is prominent with tetrahedrally coordinated Cu. The lower coordination number of Cu significantly benefits NO reduction but negatively impacts the CO-NO reaction, albeit positively influencing NO reduction in three-way catalytic reactions.

Effect of alkali addition on a Cu/SmCeO2 @TiO2 catalyst for NO reduction with CO under oxidizing conditions

The accumulation of alkali metals generated during biomass combustion onto the catalysts employed for off-gas treatment can have a detrimental effect on their performance. This work investigates the effect of potassium as a model alkali on an efficient copper-based catalyst supported on SmCeO2 @TiO2. The addition of potassium modifies the redox properties of the Cu species or, more specifically, the metal-ceria interface, providing better catalytic activity for NO reduction in oxidizing conditions. SmCeO2 @TiO2 stabilizes highly dispersed copper species, and the presence of potassium introduces surface distortions that modify the lability of oxygen atoms. The results demonstrate the key role of surface defects and labile oxygen species associated with the CeO2 support. It was found that both Cu/SmCeO2 @TiO2 and K/Cu/SmCeO2 @TiO2 catalysts fully oxidized CO below 350 °C and actively reduced NO with CO in the presence of excess oxygen, reaching a maximum NO conversion of 65% at 316 °C and 83% at 330 °C, respectively, while undesired NO2 release was minimized in the alkaline-loaded sample.

Effect of interaction degree between Mn and Ce of MnOX-CeO2 formulation on NO reduction and o-DCB oxidation performed simultaneously

MnOX-CeO2 catalysts were prepared by different methods in order to assess the influence of Mn and Ce interaction on the catalytic activity of NO reduction and 1,2-dichlorobencene (o-DCB) oxidation carried out simultaneously. Changes on catalytic properties were evaluated by XRD, Raman, N2-physisorption, H2-TPR and NH3-TPD. The samples prepared by co-precipitation and sol-gel exhibited the best catalytic activity over the whole temperature range. These preparation methods provide high interaction between Mn and Ce at surface and bulk, which was evidenced by the formation of mixed oxide phase. According to characterisation, the enhancement of catalytic activity with Mn and Ce interaction is associated to the promotion of structural defects, which improve redox and acid properties. Oxidative capability is also improved as a consequence of the oxygen vacancies generated by the presence of those structural defects. On the other hand, the promotion of Mn and Ce interaction favours the production of N2O in NO reduction at a lower temperature, and also leads to o-DCB total oxidation by decreasing CO production.

Effect of Cu-Doped Co-Mn Spinel for Boosting Low-Temperature NO Reduction by CO: Exploring the Structural Properties, Performance, and Mechanisms.

Cobalt-manganese spinel catalysts performed unsatisfactory activity at low-temperature and narrow reaction temperature window, which greatly limited the application in NO reduction by CO. Herein, we synthesize a series of Cu-doped CoMn2O4 catalysts and apply to NO reduction by CO. The Cu0.3Co0.7Mn2O4 exhibited superior catalytic performance, reaching 100% NO conversion and 80% N2 selectivity at 250 °C. Detailed structural analysis showed that the introduced Cu replaces some Co in tetrahedral coordination to induce a strong synergistic effect between different metals. This endows the catalyst with the promotion of both electron transfer and oxygen vacancy generation on the catalyst surface. Importantly, the reaction mechanism and pathway were further revealed by in situ diffusion Fourier transform infrared spectroscopy (DRIFTS) and density functional theory (DFT) calculations. The results indicated that the cycle of oxygen vacancy mainly determines the catalytic activity of NO reduction by CO. Notably, Cu doping significantly lowered the energy barrier of the rate-determining step (*CO + O → *Ov + CO2), facilitating the desorption of the CO2 and exposing the active sites for efficient NO reduction with CO. This work offers an effective way for designing the catalyst in NO reduction by CO and provides a reference for exploring the catalytic mechanism of the reaction.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide

Parallel to CO2 emission, NOx emission has become one of the menacing problems that seek a simple, durable, and high-efficiency deNOx catalyst. Herein, we demonstrated simple syntheses of platinum group metal nanoparticle-decorated f-BNNT (PGM = Pd, Pt, and Rh, and f-BNNT stands for -OH-functionalized boron nitride nanotubes) as a catalyst for efficient and selective reduction of NO by CO at low-temperature conditions. PGM/f-BNNT with a low amount of noble metal nanoparticles (0.7-0.8 wt %) presents very efficient catalytic activity for NO reduction as well as CO oxidation during their removal process. The removal efficiencies of NO and CO with Pd/f-BNNT, Pt/f-BNNT, and Rh/f-BNNT catalysts were investigated under various temperatures, flow rates, and reaction times, respectively. For most cases, NO catalytic reduction with CO reaction was >99% at a temperature as low as ∼200 °C. The catalyst robustness and efficiency were also verified by presenting almost 100% conversion of NO using a Rh/f-BNNT catalyst, which was aged under humid air at 600 and 700 °C for 24 h, respectively. The synergic effect of the catalytic efficacy of the well-dispersed noble metal nanoparticles and the excellent surface properties of BNNT are reasons for the high selectivity and catalytic property at a low temperature. On the basis of this investigation, we demonstrated that the noble metal nanoparticle-decorated f-BNNT catalysts are possible to save expensive PGM catalysts, such as Pt, Pd, and Rd, as much as 100 times while presenting similar or better catalytic performance for simultaneous NO and CO removals.

Hexagonal boron nitride nanoribbon as a novel metal-free catalyst for high-efficiency NO reduction to NH3

Electrochemical NO reduction is taken as a promising avenue to eliminate detrimental NO into valuable NH3 for a balanced nitrogen cycle. Current electrocatalysts for NO reduction are mainly focused on metal-bearing catalysts, while metal-free catalysts with low cost, excellent stability, activity and selectivity are strongly desired. Herein, we report hexagonal boron nitride nanoribbons (BNNRs) as novel metal-free catalysts for efficient NO adsorption and reduction into NH3. Our results reveal that bare edge B atoms of armchair and zigzag BNNRs act as active sites for spontaneous chemisorption and activation of NO, originating from significant electron transfer. Notably, in the subsequent NO reduction, NH3 can be spontaneously produced by armchair BNNR with a limiting potential (UL) of 0 V, which is superior to most well-established single-atom, biatom and pure traditional metal catalysts. The awesome catalytic activity for NO reduction is intrinsically introduced by the suitable NO adsorption strength on armchair BNNR, which is illuminated to appropriate electronic interactions between the active site and NO. Moreover, the catalytic selectivity of armchair BNNR for NH3 production at both low and high NO coverage can be well guaranteed due to the higher thermodynamic energy barriers in generating N2O, N2 and H2. Overall, our findings pioneer the catalytic application of BNNR and unveil the veil of metal-free catalysts for direct NO reduction to NH3.

Understanding the Catalytic Deactivation upon Hydrothermal Aging at 850 °C of WO3/Fe-Cu-ZSM-5 Catalyst for Selective Catalytic Reduction of NO by NH3

A WO3/Fe-Cu-ZSM-5 catalyst was prepared using the solid state ion exchange method (SSIE) and its performance for the Selective Catalytic Reduction of NO with NH3 (NH3-SCR of NO) was investigated. The study shows that the tungsten addition can slightly improve the high temperature catalytic activity of Fe-Cu-ZSM-5. The influence of hydrothermal aging at 850 °C for 5 h on the structural and textural properties of WO3/Fe-Cu-ZSM-5 was also studied in this paper. The XRD and FE-SEM measurements did not indicate a breakdown of the zeolite structure upon steam treatment for both aged catalysts. The aged W-base catalyst demonstrates a lower deactivation and better catalytic activity for NO reduction than the bimetallic catalyst after hydrothermal aging despite the lower acidic properties as shown by FTIR-Pyr spectroscopy owing to the presence of tungsten oxide crystallites. The “severe” stage of aging occurring in the absence of W led to the formation of copper oxide agglomerates detected using STEM and H2-TPR techniques being responsible for the deterioration of SCR activity of the aged Fe-Cu-ZSM-5.

Mechanistic study on three-way catalysis over Pd/La/Al2O3 with high La loading

Although La-loaded Al2O3 (La/Al2O3) is a widely used support material for three-way catalysis (TWC), little is known about the promotional effect of La in the La/Al2O3 supported Pd catalyst (Pd/La/Al2O3) in the catalytic NO reduction (DeNOx) for automotive emission control. Previously (Jing et al., 2020 [1]), we assessed the promotional effect of La and observed that the supported metallic Pd nanoparticles on the La/Al2O3 support were more electron-deficient than those on Al2O3 without La, which led to suppression of CO poisoning and a higher catalytic activity for NO reduction. Here, we further investigated the role of La in Pd/La/Al2O3 for the DeNOx process by various spectroscopic methods. The results obtained suggest that the efficient generation of nitrite species and its facile reactivity are important for the promotional effect of La in NO reduction. In addition, we investigated the effects of hydrothermal aging. For the TWC, Pd/La/Al2O3 with high La loading (15 wt%) was identified to be superior to the conventional industrial catalyst having a loading of 5 wt%. It was also found to show relatively high Pd dispersion even after aging at 800 °C. The observed stabilizing effect is an important benefit of the addition of La.

Preparation and evaluation of catalysts of highly dispersed zerovalent iron (Fe0) supported on activated carbon for NO reduction

Catalysts of highly dispersed zerovalent iron (Fe0) supported on activated carbon were prepared and their catalytic activity in NO reduction by CO was studied in a fixed-bed reactor. The catalytic activity improved with increasing temperature, Fe loading and dispersion. At 325 °C, the NO conversion reached 85% in the presence of CO. N2 adsorption–desorption, XRD, SEM, TEM, XPS, ICP-AES, TGA-MS/FTIR and In-situ XRD were applied to characterise the fresh and spent catalysts. Fe0 in the catalyst is better dispersed at lower Fe loadings and at lower calcination temperatures. The mechanism of NO reduction with or without CO was different. Increasing Fe0 dispersion improves the catalytic activity in the presence of CO, while increasing Fe loading is more important in maintaining the catalytic activity in the absence of CO. Catalyst deactivation is attributed to NO oxidation of Fe0 and activated carbon support as well as Fe sintering and agglomeration. CO in the reacting stream plays an important role in enduring the catalytic performance by protecting Fe0 from being oxidised by NO.

Comparative study of structure-catalytic activity relationship for Ni–Cr–Al–O and Cu–Ni–Cr–Al–O spinel oxide solid solutions

A spinel solid solution expressed by a composition formula of CuxNi1−xAl1.8Cr0.2O4 (0 ≤ x ≤ 0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl1.8Cr0.2O4 (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C3H6 oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Mars–van Krevelen mechanism.

Effects of Ni loading on the physicochemical properties of NiOx/CeO2 catalysts and catalytic activity for NO reduction by CO

The NO reduction by CO reaction was investigated using NiOx/CeO2 catalysts with different Ni loadings. Surface NiOx controls the catalytic activity which was related to the molecular structure and reducibility of the catalysts.

A catalyst with the better catalytic activity for NO reduction showed bigger reduction capacity and limiting current

The catalytic activity of a new catalyst for NO reduction is usually obtained by a gas-solid phase experiment. For the first time, a relationship has been established between catalytic performance and electrochemistry property. A bimetallic catalyst showed a low-temperature activity and removed 67.27% of NO at 300 °C, 33.39% bigger than a single-metallic catalyst. The bimetallic catalyst removed 9.770 mmol/g of NO after 1440 min, 5.212 mmol/g bigger than the single-metallic one. At the same time, the bimetallic catalyst showed a reduction capacity of 0.441 mmole/g. In comparison, the single-metallic one only had 0.242 mmole/g. Moreover, the limiting current of bimetallic catalyst (4.020 e−4A) was also bigger than that of single-metallic one (3.698 e−4A). Therefore, a catalyst for NO reduction showed better catalytic activity and electron-transfer ability at the same time. In other words, the catalytic activity of a catalyst can be potentially estimated by detecting its electrochemistry properties.

Promotion of La(Cu0.7Mn0.3)0.98M0.02O3−δ (M = Pd, Pt, Ru and Rh) perovskite catalysts by noble metals for the reduction of NO by CO

To evaluate the structural and spectroscopic steering factors of noble metal promotion in the catalytic reduction of NO by CO, a series of La(Cu0.7Mn0.3)0.98M0.02O3−δ (M = Pd, Pt, Ru, Rh) perovskite catalysts is investigated. The materials are synthesized by a sol-gel method and characterized by X-ray powder diffraction (XRD), electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). All metal-promoted perovskites exhibit a comparatively higher activity for catalytic reduction of NO by CO with respect to pure La(Cu0.7Mn0.3)O3−δ . Among all catalysts tested, the La(Cu0.7Mn0.3)0.98Pd0.02O3−δ perovskite shows the highest catalytic activity, which is tentatively related to a combined synergistic effect of improved oxygen vacancy activity and noble metals. Additionally, the redox chemistry of the catalysts in different reducing (H2) and oxidizing (NO, O2) atmospheres is tested. An enhanced kinetic reducibility, especially with Pd, was observed. All the H2-reduced catalysts are capable of reducing NO. At low and intermediate temperatures, the formation of N2O is observed, but at higher temperatures NO is exclusively converted to N2. The introduction of noble metals leads to new adsorption sites for NO. As XPS suggests a tendency for depletion of noble metals in the surface-near regions, while the catalytic activity in NO reduction at the same time appears much improved, directed noble metal promotion with modest amounts especially in surface-near regions during synthesis appears as an encouraging method to economize the use of the latter.

Efficient oxygen storage property of Sr–Fe mixed oxide as automotive catalyst support

Pd/Sr3(Fe0.8Ni0.2)2O7−δ showed a high catalytic activity for NO reduction under a wide range of oxygen concentrations due to the excellent oxygen storage capacity.

Catalytic reduction of nitrogen oxide by carbon monoxide, methane and hydrogen over transition metals supported on BEA zeolites

Different metals were impregnated onto BEA zeolites supports by ion-exchanging method to prepare catalysts for NO reduction. Activities of the prepared catalysts were then examed in a fixed bed reactor for NO reduction by CO, H2, and CH4. Experimental results indicated that Cu-BEA shows high catalytic activity for NO reduction by CO and H2 at 300 °C–500 °C, while Co-BEA shows high catalytic activity of NO reduction by CH4 at 400 °C–500 °C. Activities of all the catalysts increase as the temperature rises. Then characterization of H2-TPR, XED, XPS and BET were conducted used to investigate the physical and chemical properties of these BEA catalysts. In-situ Fourier transform-infrared spectroscopy was also used to study the mechanism of the reaction of NO reduction by CO, CH4 and H2. The reason of different activities over different BEA catalysts was then carefully explored.

Selective catalytic reduction of NO with CO and C3H6 over Rh/NbOPO4

The selective catalytic reduction of NO with C3H6 and CO was investigated over platinum group metal (PGM; Pd, Rh, or Pt) supported on NbOPO4. Rh/NbOPO4 exhibits a lower light-off temperature of NO reduction to N2 compared to Pd- or Pt-loaded NbOPO4 catalysts and Rh/Al2O3 under stoichiometric conditions. Rh/NbOPO4 shows superior catalytic activity for NO reduction to Rh/Al2O3 under a wide range of lean conditions. Propylene (C3H6) was partially oxidized to reactive aldehyde species on Rh/NbOPO4, whereas less-reactive carboxylate species was generated and adsorbed on Rh/Al2O3. A highly dispersed Rh0 nanoparticles on NbOPO4 was slowly oxidized by exposure to excess O2, but Rh on Al2O3 was readily oxidized to less-active Rh2O3. The high activity of Rh/NbOPO4 for C3H6 oxidation to reactive aldehyde species and the resistance of Rh0 against oxidation results in the enhancement of NO reduction activity in a slightly lean region.

Iron based monolithic catalysts supported on Al2O3, SiO2, and TiO2: A comparison for NO reduction with propane

The selective catalytic reduction of NO with propane has been investigated with iron based monolithic catalysts supported on alumina, silica, and titania. The catalysts were characterized by N2-physisorption, XRD, SEM, XPS, H2-TPR, Py-FTIR and in situ DRIFTS technologies. The different supports had a significant influence on specific surface area, surface morphology, lattice oxygen, redox properties and the acid sites, which resulted in differences in the catalytic activity of NO reduction. The C3H8-SCR performance decreased in the order as Fe/Al2O3/CM > Fe/SiO2/CM > Fe/TiO2/CM. Fe/Al2O3/CM showed the highest activity with a nitrogen oxide conversion of 100% in the presence of oxygen at 500 °C,which is mainly attributed to the good redox properties and the abundant Lewis acid sites. Based on in situ DRIFT studies, the increase of Lewis acid sites will enhance the formation of NO2/NO3− species and acetate/formate species, then promote the catalytic activity.

The study on continuous denitrification, desulfurization of pyrolusite/activated coke hybrid catalyst

The SO2 removal and regeneration of ACP improved its NO removal activity, while the denitrification had almost no effect on the desulfurization. The metal sulfate of ACP-Rn showed catalytic activity for NO reduction although there is also a reverse effect.

Selective reduction of NO over Cu/Al2O3: Enhanced catalytic activity by infinitesimal loading of Rh on Cu/Al2O3

This study demonstrates that an isolated Cu2+ species formed by interacting with tetrahedral Al species on γ-Al2O3 shows a high catalytic activity for NO reduction with C3H6 and CO under high oxygen concentrations (lean conditions), and that an infinitesimal amount of Rh (0.01wt%, 100ppm) loaded on 0.5wt% Cu/Al2O3 is a more effective catalyst for the reactions, under a wide range of oxygen concentrations, than 0.5wt% Pd/Al2O3 or 1.0wt% Rh/Al2O3. Although 0.5wt% Cu/Al2O3 itself is effective for the reaction at lean conditions, it shows low catalytic activity under stoichiometric and low oxygen concentrations (rich conditions). On the other hand, the loading of 0.01wt% Rh on Cu/Al2O3 dramatically improves catalytic activities under stoichiometric and rich conditions, with maintaining the high NO reduction activity of Cu/Al2O3 itself under lean conditions. Therefore, a Rh species in the Rh/Cu/Al2O3 system must play a role as an active site under stoichiometric and rich conditions. Under lean conditions using Rh/Cu/Al2O3, an isolated Cu2+ species on γ-Al2O3 mainly contributes to the NO reduction properties of the catalyst. No such advantage was observed for Pd/Cu/Al2O3; that is, the catalytic activity of Cu/Al2O3 under lean conditions is diminished by Pd loading. Hence, we reveal that the roles of the Rh and Cu species in the Rh-loaded Cu/Al2O3 catalyst are effectively shared according to oxygen concentration in selective reduction of NO, when loaded with an infinitesimal amount of Rh. These observations provide novel guidelines for the development of catalysts that more beneficially use precious metal resources.

Preparation of Ir@Pt Core–Shell Nanoparticles and Application in Three-Way Catalysts

The Ir@Pt core–shell spherical nanoparticles with Pt deposited on Ir cores were synthesized for the first time using successive reduction method based on epitaxial growth. The Ir@Pt/SiO2 core–shell structure catalysts were used in the three-way catalysts of controlling automobile exhaust emission, which exhibited high catalytic activity of NO reduction in three-way catalytic reaction.