H2O Tolerance Research Articles

Architecture of core-shell Ce-OMS-2@CeO2 catalyst and its SCR activity and SO2+H2O tolerance performance at low-temperature

It is a challenge to develop highly sulfur dioxide and water (SO2+H2O) resistance for the low-temperature selective catalytic reduction (SCR) catalysts of nitrogen oxide (NOx) in the non-electric-power industry. In this paper, core-shell and loaded type of Ce-OMS-2 complexes (Ce-OMS-2@CeO2 and CeO2/Ce-OMS-2) were successfully prepared. Their textural properties were characterized and catalytic performance were carried out. The results showed that the core-shell Ce-OMS-2@CeO2 material could maintain the mesoporous structure and significantly improve the mass transfer and adsorption of the reaction gas NO, thus improving the SCR efficiency. On the contrary, for the loaded CeO2/Ce-OMS-2 catalyst, large amounts of CeO2 deposited on the surface of Ce-OMS-2 and blocked the mesoporous structure. Furthermore, SO2 reacted with CeO2/Ce-OMS-2 to form lots of metal sulfate (manganese sulfate or cerium sulfate), which led to the deactivation of the active Mn sites. Therefore, the CeO2/Ce-OMS-2 catalyst exhibited the low SCR activity and poor SO2+H2O tolerance during the SCR reaction. We also clarify the reason for the anti-sulfur of core-shell Ce-OMS-2@CeO2 catalyst. In the presence of SO2 and H2O, SO2 could easily react with NH3 and H2O to produce ammonium bisulfate (NH4HSO4, ABS) on the surface of the Ce-OMS-2 and CeO2/Ce-OMS-2 catalysts. Then ABS can be physically deposited on the surface of the catalysts, thus blocking the active Mn sites to participate in the SCR reaction. Interesting, for the core-shell Ce-OMS-2@CeO2 catalyst, the formed ABS could significantly be decomposed at low temperature, leading to the exposure of surface active Mn sites of the catalyst. Herein, it could maintain the efficient SCR performance over the Ce-OMS-2@CeO2 catalyst. A dynamic balance of ABS formation and decomposition was achieved over Ce-OMS-2@CeO2 even at low temperatures, which hindered the SO2 poisoning during the NH3-SCR reaction. As expected, the core-shell Ce-OMS-2@CeO2 catalyst showed excellent SCR performance and SO2+H2O resistance (~100% NO conversion in the temperature range of 100–200 °C without SO2, ~80% NO conversion for 4 h in the presence of SO2). This work provides an effective strategy for the development of efficient and stable Mn-based low-temperature SCR catalysts.

The enhanced SO2 resistance of Fe-Ti catalyst by W/SO42− co-modification for NH3-SCR: A combined experimental and DFT study

It remains a great challenge to improve the low-temperature SO2 resistance of catalysts applied for selective catalytic reduction of NOx with NH3 (NH3-SCR). This work develops an outstanding SO2-tolerant Fe-Ti (FT) catalyst by W/SO42− co-modification via a sol–gel method using Fe(NO3)3·9H2O, tetrabutyl titanate, ammonium tungstate and thiourea as raw materials. The physicochemical characterizations, in-situ diffuse reflectance infrared Fourier transform (DRIFT) measurements and density functional theory (DFT) calculations were combined to reveal the underlying mechanisms. Although W doping can effectively enhance the surface acidity, NH3 adsorption on Lewis acid sites can still be restrained by competitive adsorption of SO2, whereas SO42− modification can enhance the adsorption stability of NH3 without being affected by SO2. Simultaneously, the NO adsorption ability on Fe sites can be significantly enhanced by W/SO42− co-modification. Furthermore, the W doping or SO42− modification can induce conversion of Fe3+ to Fe2+ to affect the redox property of Fe species. A proper amount of Fe2+ suppressed the oxidizability of FT catalyst to inhibit NH3 overoxidation to enhance N2 selectivity, and created more oxygen vacancies to generate larger amount of chemisorbed oxygen to facilitate NH3 dehydrogenation and NO oxidation. More importantly, the inhibition effect of SO2 adsorption on Fe sites was strengthened by W/SO42− co-modification. Consequently, the W/SO42− co-modified FT catalyst exhibited high activity with >90 % of NO conversion and >95 % of N2 selectivity within a broad window of 275–450 °C and possessed superior SO2 + H2O tolerance at 275 °C.

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Enhanced activity and water resistance of SiO2-coated Co/In-SSZ-13 catalysts in the selective catalytic reduction of NOx with CH4

CH4 selective catalytic reduction of NOx (CH4-SCR) is a promising technology to synergistic control of CH4 and NOx emission from LNG-powered vehicles and ships, while its insufficient catalytic activity and H2O resistance are key barriers for application. In this work, SiO2 coated Co3O4/In-SSZ-13 catalysts (Co/In-Z@Si) were prepared to simultaneously improve the CH4-SCR activity and H2O tolerance. The proper Co3O4 introduction enhanced the catalytic performance of the In-SSZ-13, while excessive amount of Co3O4 addition led to more CH4 being oxidized and insufficient CH4 participating in the CH4-SCR reaction. There was a “seesaw effect” between NO oxidation and CH4 oxidation performance of the catalysts. The H2O resistance of the Co/In-Z catalysts significantly enhanced via ultrathin SiO2 coating. The NOx and CH4 conversion maintained 81 % and 90 % in the presence of H2O at 500 °C for the Co/In-Z@Si catalyst, respectively. The in situ DRIFTS confirmed that the SiO2 coating could adsorb H2O molecules, prevent H2O from contacting the active sites, and limit the competitive adsorption between H2O and CH4 on the catalyst. This work provides a good candidate with superior catalytic performance and H2O resistance for removal of NOx and CH4 from LNG-powered vehicles and ships simultaneously.

New insights into improved SO2＆H2O resistance over MoCrCeOx catalyst by CTAB for medium-low temperatures NH3-SCR: Regulation of surface acid and oxygen species

Selective catalytic reduction (NH3-SCR) of NH3 is the most efficient NOx removal technology. Improving the SO2/H2O resistance of SCR catalyst is of great importance for its industrial application. The Mo(0.3)-CrCeOx catalysts synthesized by the citric acid method exhibited excellent high concentration SO2 resistance but poor H2O tolerance. In this work, cetyltrimethylammonium bromide (CTAB) was used to improve SO2＆H2O resistance over Mo(0.3)-CrCeOx catalyst at medium-low temperatures. The mechanism of CTAB modification and the discrepancy to citric acid (CA) method were investigated. The results indicated that the CTAB catalyst had a large specific surface area, and was conducive to forming a specific structural strength. The enhancement of surface acidity of CTAB is the reason for the further enhancement of SCR activity. The regulation of hydroxyl oxygen to promote the activation of Brønsted acid sites is the key factor to SO2＆H2O resistance. In addition, the in-situ DRIFTS results revealed the different mechanisms of the two catalysts. This paper raised the deactivation reason of sol-gel catalyst caused by SO2＆H2O and presented an effective modification strategy.

Revealing the boosting roles of sulfate groups on NOx selective catalytic reduction over V2O5/CeO2 catalyst

Ceria-supported vanadia (VOx/CeO2) catalyst has been extensively investigated in the field of NOx selective catalytic reduction with NH3 (NH3-SCR) but is limited in practical application owing to its poor sulfur resistance and high-temperature activity. Herein, a series of SO42− modified V2O5/CeO2 catalysts were fabricated to improve the overall catalytic performance. The 2 %SO42−-V2O5/CeO2 catalyst exhibited above 95 % NOx conversion, 90 % N2 selectivity in the temperature range of 225–400 °C and excellent SO2 + H2O tolerance, which was much better than V2O5/CeO2 catalyst. Characterization results showed that the introduction of SO42− over V2O5/CeO2 increased the Ce3+/(Ce3++ Ce4+) ratio to promote the formation of oxygen vacancies and promoted the generation of more conducive polymeric vanadyl species. The synergistic effect of the redox sites and acid centers provided moderate redox property and enhanced surface acidity, thus improving the adsorption of NH3 and inhibiting the over-oxidation of NH3 that occurs on V2O5/CeO2. In-situ DRIFTS indicated that the NOx reduction over V2O5/CeO2 and 2 %SO42−-V2O5/CeO2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. This study can expound the reasonable design of vanadium-based catalysts for efficient NOx reduction in industry.

Sb-loaded MnOx/TiO2/CNTs catalysts for selective catalytic reduction of NOx: insight to the SO2 and H2O tolerance

PurposeThis paper aims to synthesize and test Mn-Sb/TiO2-CNT catalysts with different Sb/Mn molar ratios to be used in NH3-SCR reaction.Design/methodology/approachA series of Sb-loaded carbon nanotubes (CNTs)-based Mn/TiO2 catalysts were prepared by the incipient wetness co-impregnation method and tested for the selective catalytic reduction (SCR) of NOx with NH3.FindingsThe Sb-loaded Mn/TiO2-CNTs catalyst outperformed other catalysts and presented the highest activity in the temperature regime of 100–400°C. The catalyst loaded with Sb also showed good SO2 and H2O resistance and exhibited better thermal stability. A stepwise study of SO2 addition evidenced that Mn-Sb/TiO2-CNTs catalyst exhibited better SO2 resistance than the base catalyst Mn/TiO2, where the Sb doping greatly inhibited the sulphating of active phase of the catalyst.Originality/valueIn Sb-loaded catalysts, the formed SOx species fused with SbOx instead of MnOx. This favoured interaction of SO2 with SbOx successfully prevents the MnOx from being sulphated by SO2 which substantially improves the SO2 tolerance of Sb-loaded catalysts.

Puffy hierarchical nanonet structured multifunctional membranes for NO degradation and ultrafine dust filtration

Multifunctional nanofibrous catalytic membranes are used for comprehensive treatment of fine particulate matter (PM) and toxic gaseous contaminants. However, the need for high purification efficiency with low resistance presents a unique challenge. Herein, a method of optimizing the morphology of manganese oxide (MnOx) on Zr-TiO2 (TZ) nanofiber membranes was developed to remove ultrafine PM and nitric oxide (NO) efficiently with relatively low pressure drops. After tailoring the hydrothermal solution properties, the MnO2 ultrafine nanowires (≈22 nm) and Mn3O4 nano-octahedra assembled with scaffold nanofibers formed dual-network structures with high gas permeabilities, superior redox properties, and abundant surface acidities. The resultant M2TZ (2-MnOx/Zr-TiO2) catalytic membranes exhibited exceptional NH3 selective catalytic reduction (NH3-SCR) activity (T90 = 215 °C) with a gas hourly space velocity of 75,000 h−1, as well as outstanding SO2 and H2O tolerance and long-term stability. Meanwhile, owing to the puffy hierarchical nanonet structure, the M2TZ catalytic membranes also show a high filtration efficiency of 99.99% for PM0.3 removal with a low air resistance of 125 Pa, high air permeability of 1259 m3 m−2 h−1 kPa−1, and satisfactory PM capture at 300 °C. This work may shed light on the design of advanced multifunctional membranes for air pollutant purification.

Low-temperature selective catalytic reduction of NOx with NH3: Exploring the mechanism of enhancing H2O tolerance through methylation functionalization and structural regulation in IPAx-Mn-BTC

In the selective catalytic reduction (SCR) of NOx with NH3, it is crucial to design low-temperature de-nitrification (de-NOx) catalysts with high H2O tolerance. Here, we developed a type of low-temperature de-NOx catalyst (IPAx-Mn-BTC) with strong H2O tolerance through methyl functionalization. In the presence of the optimal catalyst (IPA50-Mn-BTC), the NOx conversion only decreased from 97% to 90% after introducing 6% H2O for 6 h at low temperature of 150 °C. The results of in-situ DRIFTS and density functional theory calculations confirm that the de-NOx reaction process and the generation of intermediate states that occur on the surface of the IPA50-Mn-BTC are not affected by H2O. The elimination of the small pore size (< 4.3 nm) and the diminished H2O adsorption energy resulted from methyl functionalization are the key factors behind the improved H2O tolerance. This work provides a new approach for designing low-temperature de-NOx catalysts with high H2O tolerance.

High performance iridium loaded on natural halloysite nanotubes for CO-SCR reaction

Iridium nanocatalysts are ideal candidates for the selective catalytic reduction of NOx by CO (CO-SCR) in excess oxygen. Here, a high-performance Ir nanocatalyst supported on natural halloysite nanotubes (HNTs) was applied for the CO-SCR. The HNTs loaded with only 0.5 wt% Ir achieved 78 % NOx conversion at 250 °C in the presence of 5 % O2, which was the highest among catalysts with varied Ir loadings or reduction temperatures. It also possessed an excellent SO2 and H2O tolerance during longevity tests. An interesting SO2-enhanced CO-SCR long-term stability was observed, which was ascribed to the inhibitory effects of SO2 on the side reaction between CO and O2. The loading amount and the reduction temperature could modulate the size of Ir nanoparticles and the percent of Ir0, which were two key factors determining the CO-SCR activity. DRIFTS characterizations and DFT calculations coherently revealed the favorable adsorption sites of CO (top) and NO (hcp) on Ir nanoparticles. The Ir atoms served as a charge transfer bridge from the C atom of CO to the N atom of NO, leading to the enhanced breakage of N-O bonds. This work provides Ir/HNT as a promising CO-SCR material with high performance and robustness to tackle NOx pollution.

Uncovering the centrality of mono-dentate SO32-/SO42- modifiers grafted on a metal vanadate in accelerating wet NOX reduction and poison pyrolysis

NOX rarely binds with labile oxygens of catalytic solids, whose Lewis acidic (LA) species possess higher binding strengths with NH3 (ENH3) and H2O than Brönsted acidic counterparts (BA--H+; -OH), oftentimes leading to elevate energy barrier (EBARRIER) and weaken H2O tolerance, respectively. These limit NH3-assisted wet NOX reduction via Langmuir-Hinshelwood-type or Eley-Rideal (ER)-type model on LA species, while leaving ER-type analogue on BA--H+ species proper to reduce wet NOX. Given hard-to-regulate strength/amount of -OH species and occasional association between ENH3 and EBARRIER, Ni1V2O6 (Ni1) was rationally chosen as a platform to isolate mono-dentate SO32-/SO42- species for use as BA--H+ bonds via protonation to increase collision frequency (k’APP,0) alongside with disclosure of advantages of SO32-/SO42--functionalized Ni1V2O6 (Ni1-S) over Ni1 in reducing wet NOX. Ni1-S outperformed Ni1 in achieving a larger BA--H+ quantity (k’APP,0↑), increasing H2O tolerance, and elevating oxygen mobility, thus promoting NOX reduction activity/consequences under SO2-excluding gases. V2O5-WO3 composite simulating a commercial catalyst could isolate mono-dentate SO32-/SO42- species and served as a control (V2O5-WO3-S) for comparison. Ni1-S was superior to V2O5-WO3-S in evading ammonium (bi-)sulfate (AS/ABS) poison accumulation and expediting AS/ABS pyrolysis efficiency, thereby improving AS/ABS resistance under SO2-including gases, while enhancing resistance against hydro-thermal aging.

Insights into the simultaneously enhanced activity, selectivity, and H2O resistance of cobalt modified MnCeOx/TiO2 catalyst for selective catalytic reduction of NOx with NH3

The promotional effect of cobalt (Co) modification on MnCeOx/TiO2 catalyst for selective catalytic reduction of NO with NH3 (NH3-SCR) was investigated extensively in this study. A series of CoMnCeOx/TiO2 catalysts with different Co contents were prepared by the facile impregnation method and characterized by XRD, N2 sorption, XPS, H2-TPR, NH3/NO-TPD, and in situ DRIFT spectroscopy. The results indicate that the modification of MnCeOx/TiO2 by Co could significantly improve its low-temperature activity and N2 selectivity, and broaden operation temperature window (>95% NO conversion at 100–225 °C), and that the optimal mole ratio of Co to Ti in the catalyst is 0.4. Furthermore, the introduction of Co to MnCeOx/TiO2 could obviously enhance H2O resistance. The characterization results reveal that the addition of Co to the MnCeOx/TiO2 catalyst could enhance the dispersion of MnOx and CeOx, and increase the relative ratio of Mn4+ and Ce3+ on the catalyst surface. In addition, the surface area of MnCeOx/TiO2 is enlarged evidently after doping of Co. From the results of H2-TPR, NH3/NO-TPD, and NO oxidation, CoMnCeOx/TiO2 exhibits stronger reducibility, larger adsorption capacity for NH3 and NO, and higher NO to NO2 conversion than MnCeOx/TiO2, thus obtaining the higher SCR activity, N2 selectivity, and H2O tolerance. In situ DRIFT spectroscopy tests indicate that the NH3-SCR reaction on both MnCeOx/TiO2 and CoMnCeOx/TiO2 follow simultaneously the Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Revealing the effect of electronic interaction between dual redox sites on CeO2-Fe2O3 NH3-SCR catalyst through interface contact tailoring

Due to the requirements of different applications environments, higher catalytic activity or SO2 and H2O tolerance, the binary or ternary metal oxide NH3-SCR catalysts with dual redox sites have been widely studied in recent years. The electronic interaction between the dual redox sites has a significant impact on the catalyst performance. Herein, a series of CeO2-Fe2O3 composite catalysts with continuously enhanced interface contact as well as electronic interactions were prepared through a facile grinding method. The activity tests showed that neither the catalyst with the least interfacial contacts nor the one with the greatest interfacial contacts exhibited the highest NOx removal activity. The comprehensive characterizations demonstrated that the apparent physicochemical properties including the NH3 adsorption ability, redox property, and so on, changed in favor of NH3-SCR reaction when enhancing the interface contact for the CeO2-Fe2O3 composite catalysts. However, the reaction mechanism as well as the reactivity of main NH3 and NO adsorbed species were also altered by the electronic interactions between Ce and Fe active species. The unsatisfactory NOx removal activity of the CeO2-Fe2O3 catalyst with strongest electronic interactions between Ce and Fe active species was explained by the reactivity of main NH3 and NO adsorbed species. This work can provide new ideas for improving the performance of NH3-SCR catalysts through changing the interface contact and electronic interaction between the dual redox sites.

Catalysts prepared from solid wastes for efficient removal of NOx in NH3-SCR process: A review

The increase of solid wastes exerted great pressure on the environment and even damaged human health. Given this, the resource utilization of solid wastes became an inevitable trend of the industrial development. However, many researchers recognized that solid wastes with the component of Fe2O3, SiO2, Al2O3, TiO2, etc., could be utilized as the low-cost materials for preparing NH3-SCR catalysts, which could solve both the accumulation of solid wastes and the emission of NOx in industrial processes. Herein, some typical solid wastes, such as blast furnace slag (BFS), red mud (RM), coal fly ash (CFA), Fenton sludge (FS), etc., were extensively studied for their potential in NH3-SCR catalysts. Although the presence of some harmful components in solid wastes led to catalysts deactivation, they could still be excellent supports applied on NH3-SCR catalysts after proper pretreatment. In fact, these catalyst supports derived from solid wastes provided larger specific surface areas, thereby enhancing the NH3 adsorption and redox capacity and facilitating the active ingredients loaded uniformly. Meanwhile, some useful impurities in solid wastes might also facilitate the NH3-SCR performance, achieving denitrification efficiency comparable to other catalysts made from costly materials. Moreover, most of these NH3-SCR catalysts performed significant SO2 and/or H2O tolerance via metal oxides-doping, which would expand their potential for practical application in industry. Finally, the prospects for the application of solid wastes in NH3-SCR catalysts were also proposed.

Dual improvement in acid and redox properties of the FeOx/OAC catalyst via APS oxygen-functionalization: High low-temperature NH3-SCR activity, SO2 and H2O tolerance

Carbon-based transition metal catalysts (CTCs) have shown tremendous potential within NOx abatement, while the improvement of low-temperature NH3-SCR activity and SO2 and H2O tolerance remains challenging. Herein, we report an easily-achievable strategy to regulate the active phases of the FeOx/AC catalyst via APS oxygen-functionalization for improving in acid and redox properties and facilitating NH3-SCR activity. For redox sites, APS oxygen-functionalization boosted the metal-support interaction, immobilized γ-Fe2O3 nanoparticles highly dispersed on FeOx/OAC1.5-60-3 surface. Meanwhile, Fe valence and oxygen vacancy of FeOx were tailored by APS oxygen-functionalization, resulting in the formation of active oxygen vacancy-coupled Fe2+. For acid sites, in situ DRIFTs further confirmed that APS oxygen-functionalization enhanced the adsorption and activation properties of NH3 over the oxygen-containing functional groups (OCFGs) on FeOx/OAC1.5-60-3. Due to the improvement of acid and redox properties, FeOx/OAC1.5-60-3 delivered superior NO conversion (>90 %) at 120–250 °C and SO2/H2O resistance in comparison with FeOx/AC. Therefore, this work sheds light on a robust and pragmatic strategy for the rational design of CTCs and provides a new insight in improving catalytic performance of CTCs.

Simultaneous removal of NOx and dust with integrated catalytic filter: Interactions between NH3-SCR and filtration processes

The integrated selective catalytic reduction of nitrogen oxides by NH3 (NH3-SCR) and dust filtration technology can effectively reduce the energy consumption and space of the flue gas purification system. Herein, a novel catalytic filter is fabricated by in situ depositing FeWOx heterogeneous catalyst onto stainless-steel-fiber filter (named as FeWOx/SSFF), which displays excellent deNOx performance (>85 % NOx conversion and 96 % N2 selectivity) with superior H2O and SO2 tolerance, as well as great dedust efficiency (>99.99 % and low residual pressure drop). The suitable oxygen mobility and enhanced charge transfer ability at the crystalline-amorphous interface contribute well to the excellent SCR performance, and the low pressure drop is promoted by the well dispersion of FeWOx species on the SSFF. Notably, a volcanic relationship between dedust process and SCR performance was obtained, due to the boosting of dedust process for the denitrification, which was confirmed by computational fluid dynamics (CFD). Besides, excessive dust-cake could inhibit SCR performance owing to catalytic site being covered by dust particles. Accordingly, SCR process hardly affected dedust efficiency and residual pressure drop. This work reveals the interactions between SCR and dedust processes, and paves a way to design novel catalytic filters for simultaneously removing dust and gas pollutants at practical conditions.

Unveiling a remarkable enhancement role by designing a confined structure Ho-TNTs@Mn catalyst for low-temperature NH3-SCR reaction.

MnOx-based catalysts are considered promising alternative catalysts for NH3-SCR to remove NOx at low temperature. However, their poor SO2 or H2O tolerance and unfavorable N2 selectivity are still the main obstacles restraining their further practical application. Herein, we carefully confined the manganese oxide active species in Ho-modified titanium nanotubes to improve their SO2 resistance and N2 selectivity. Ho-TNTs@Mn exhibits excellent catalytic activity, strong SO2 and H2O tolerance and superior N2 selectivity, and more than 80% NO conversion can be achieved in the range 80-300 °C with 100% N2 selectivity. The characterization results verify that the pore confinement effect of Ho-TNTs for Mn increases the dispersion of Mn to promote the interfacial effect between Mn and Ho. The electron synergistic effect between Mn and Ho improves the electron transformation of Mn and Ho, which inhibits electron transfer between SO2 and Mn to avoid poisoning from SO2. We also find that the interaction between Ho and Mn induces electron migration to restrain the production of Mn4+, contributing to the suitable redox capacity to decrease the creation of byproducts, which serves as the motivation for high N2 selectivity. In situ DRIFTs analysis clarifies that Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms co-exist in the NH3-SCR reaction over Ho-TNTs@Mn, and the E-R reaction mechanism predominates We believe that Ho-TNTs@Mn with a well-designed nanotube structure will show preferable development and application prospects in the NH3-SCR reaction.

Enhancement of low temperature NH3-SCR activity and SO2 & H2O tolerance over VPO-Co/TiO2: Determining roles of acidity via Co doping

A series of VPO-Co/TiO2 samples were synthesized for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperature for the first time. The activity testing results suggested that the catalytic performance of VPO-Co/TiO2 was greatly improved after Co was introduced. Among all the catalysts, VPO-Co(0.07)/TiO2 provided the optimal low-temperature SCR activity, with NO conversion 100% and N2 selectivity above 98% at 180–270 °C. Additionally, VPO-Co(0.07)/TiO2 also presented extraordinary SO2 + H2O durability after introducing 200 ppm SO2 and 6 vol% H2O to the SCR reaction at 180 °C. The characterization results revealed that the oxidation capacity and the acidity were both improved with the Co doping. In this VPO-Co/TiO2 system, the increased acidity via the Co doping played a more critical role in raising the SCR activity. The richest surface acidity could offset the adverse effect of moderate oxidation capacity over VPO-Co(0.07)/TiO2, thus resulting in the best de-NOx performance at low temperature. Furthermore, the in-situ diffuse reflectance Fourier transform infrared spectroscopy (in-situ DRIFTS) studies revealed that the SCR reaction over VPO-Co(0.07)/TiO2 was proceeded via a combination of Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) pathways at 180 °C.

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 NOx 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.

Crystal plane induced metal-support interaction in Pd/Pr-CeO2 catalyst boosts H2O-assisted CO oxidation

Catalytic oxidation is an effective method to remove CO in exhaust gas, yet it is challenging to enhance the H2O tolerance of catalysts at low temperature due to the strong competitive adsorption between H2O and reactants (CO and O2). Here, we report that the precise control of the metal-support interaction by regulating the support crystal plane of Pd/Pr-CeO2 catalysts leads to highly efficient CO oxidation catalysts under wet conditions. The addition of H2O inhibits the CO oxidation activity of Pr-CeO2 nano-cube and octahedron supported highly dispersed Pd catalysts, but enhances the CO oxidation activity over Pr-CeO2 nanorod supported highly dispersed Pd catalysts. After introduction of H2O in feed gas, the T99 (Temperature to achieve 99 % conversion of CO) decreases from 157 °C to 115 °C for Pd/Pr-CeO2-NRs (Nanorods) catalyst at a gas hourly space velocity of 70, 000 h−1 and remains stable for more than 2000 min in the presence of H2O. Systematic characterization reveals that the (110) crystal plane of Pr-CeO2 nanorod enhance the interaction between Pd species and support, resulting in the formation of abundant high dispersed Pd-oxygen vacancy (Ov) active sites. The kinetics study and in-situ DRIFTS characterization confirmed that CO oxidation Pd/Pr-CeO2-NRs mainly follows the H2O-mediated Langmuir-Hinshelwood mechanism in the presence of H2O. H2O promote the formation of active OH groups and accelerate CO oxidation through formate pathway at low temperature. In contrast, the CO oxidation follow traditional MvK mechanism in the absence of H2O.