Surface Acidity Of Catalysts Research Articles

Increasing Lewis acidic sites and promoting electron transfer of Mn2O3 by C-hybridization to improve the peroxymonosulfate activation for Bisphenol A degradation.

The surface acidity and electron transfer performance of manganese oxide catalysts significantly affected its performance of peroxymonosulfate (PMS) activation. In this work, Mn2O3 catalyst was prepared by the precipitation method. The C-hybridization Mn2O3-D (Mn2O3-D) catalyst prepared with disodium oxalate as a precipitant had more Mn3+ and Lewis acid sites on the surface, promoting the binding of PMS on the catalyst surface, which exhibited the best performance in inducing PMS activation to degrade bisphenol A (BPA). Quenching experiments and in situ electron spin resonance (ESR) results indicated that radicals and singlet oxygen were not the main reactive oxygen species (ROSs) in the advanced oxidation process. The chemical probe experiment of phenylmethylsulfone (PMSO) showed that the ≡Mn-OOSO3- metastable intermediate formed by the binding of PMS with Mn sites on the catalyst surface was important active species for contaminants degradation. Contaminants combined with intermediates on the catalyst surface to form the electron transfer channels, which were directly degraded through oxygen-atom-transfer pathway and single-electron-transfer pathway. And the hybridization of C promoted the electron transfer during this process. This work further elucidated the reaction mechanism of PMS activation by manganese oxides, and proposed new ideas for the design of MnOx catalysts for efficient activation of PMS.

Highly Efficient Ru-VOx/TiO2 Catalysts for Hydrodeoxygenation of Amides to Amines: The Promotion Effect of Monolayer Dispersed VOx on Rutile TiO2.

The hydrodeoxygenation of amide to amine is one of the most important amine synthetic approaches in chemical engineering. However, low amide reactivity and poor amine selectivity remain big challenges for catalytic hydrodeoxygenation of amides. Here, Ru-VOx/TiO2 catalysts with different V/Ru atomic ratios were prepared with the sequential impregnation method. The physicochemical properties of catalysts were characterized by using XRD, Raman, TEM, CO chemisorption, NH3-TPD, H2-TPR, XPS, and Formamide-DRIFTS. The hydrogenation of butyramide as a model reaction was used to evaluate the catalytic performance. The butyramide conversion and butylamine selectivity varied with V/Ru atomic ratio in a volcano-type relationship, and the 2V-4Ru/TiO2 catalyst (V/Ru atomic ratio = 1) presented the best catalytic performance (96% conversion and 82% butylamine selectivity) at 423 K with 5 MPa H2. The catalyst was also reused five successive times without an obvious decline in either activity or selectivity, showing excellent stability. Based on characterization and evaluation results, the interaction between Ru nanoparticles (∼2 nm) and VOx species promoter generated abundant Ru-VOx boundary with V4+ species adjacent to oxygen vacancies (Ru-Vo-V4+). As the V/Ru atomic ratio was 1, the 2V-4Ru/TiO2 catalyst, with monolayer dispersed VOx species, presented the maximum Ru-VOx boundary and showed the best catalytic activity and selectivity to amine. The monolayer dispersed VOx species also minimized the catalyst surface acidity and suppressed the secondary side reaction. Moreover, the hydrodeoxygenation reaction evaluations of various amides including aliphatic primary amides and cyclic amides showed 90-99% conversion and 78-99% selectivity to corresponding amines, suggesting wide applicability of 2V-4Ru/TiO2 catalyst. The study provides a highly efficient strategy to improve amine selectivity in the hydrodeoxygenation of amides by optimizing the interaction between metal and metal oxide promoters.

Reduction and structural modification of MoOx/γ-Al2O3 catalysts through acetic acid treatment for green diesel production from corn distiller’s oil

Enabling new environmentally-friendly resources for fuels and platform chemicals is crucial to fulfill our future energy demands while enhancing circularity. Corn distiller’s Oil (CDO) − as a coproduct of the ethanol industry, serves as a sustainable supply of carbon that may be converted into energy, fuels and specialty chemicals. A current challenge in using renewable oxygenated feedstocks is the high amount of coking and catalyst fouling that occurs. This study examined the hydrothermal deoxygenation of CDO into green diesel using molybdenum oxide (MoOx) catalysts in a continuous process without using any external hydrogen. The possibility of reduction and developing oxygen-deficient surfaces on molybdenum oxide (MoOx) catalysts through acetic acid treatment or adding ceria (CeO2) was investigated in order to enhance the acidity of catalysts as well as catalytic activity and stability required for the production of green diesel from CDO. Results showed that the acidity of these catalysts as measured by NH3 temperature programmed desorption (NH3-TPD) had a strong correlation between the degree of deoxygenation and catalyst stability. Acetic acid treatment of the 7.5 wt% MoO3/γ-Al2O3 catalyst reduced MoO3 to MoO3-x, increased the Mo5+ species from 8.7 % to 22 %, created Mo4+ species and increased the catalyst surface acidity in the range of low to moderate strength by approximately 17 %. The use of acetic acid-treated molybdenum oxide (Hac-7.5 wt% MoO3/γ-Al2O3) catalyst enabled nearly complete (99.9 %) deoxygenation of CDO and heavy hydrocarbons cracking to produce diesel-like fuels. A moderate increase in catalyst surface acidity by acetic acid treatment also increased the selectivity of diesel-like fuel through hydrocracking of long-chain hydrocarbons. This low-cost modification step of catalyst improvement is promising for industrial application. However, cracking of hydrocarbons generated amorphous coke (no graphitic coke was observed) on the catalyst surface, which required periodic removal by controlled calcination of the catalyst in presence of air for further use.

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Boosting toluene destruction by engineering surface acidity–alkalinity in defective cobalt oxide catalyst

The surface acidity and alkalinity of catalysts played a decisive role in the destruction of Volatile organic compounds (VOCs). In this study, a series of Co3O4 catalysts were synthesized under different temperatures by calcining metal organic frameworks (MOFs). By controlling the temperature, the organic linkers were effectively eliminated, resulting in catalysts with a high specific surface area due to the preservation of the parent structure of the MOFs. Among the catalysts tested, Co3O4−350 (calcined at 350 °C) demonstrated the highest catalytic activity for toluene oxidation (T90 =231 ℃) and reliable water resistance (3 vol.% water vapor). The efficacy was attributed to the high ratio of reactive oxygen species and high valence Co species, weaken Co−O bond strength as well as high concentration of oxygen vacancies. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrate that acidity–alkalinity is crucial in the adsorption and activation, while oxygen vacancies were found to be essential for deep oxidation.

Synergistic catalysis of NO and chlorobenzene over Mn3O4-CeO2 catalysts: Acid sites, catalytic pathway and mechanism

Catalyst active sites and surface acidity are crucial for the synergistic catalysis of NOx and dioxins, determining the selectivity towards N2 and CO2. This study synthesized Mn3O4-CeO2 catalysts to investigate the influence of these sites on the catalytic performance for NO and chlorobenzene. Mn0.086Ce, made by the redox method, showed the highest Mn-Ce interface, achieving nearly complete conversion of chlorobenzene and NO at 180℃, with CO2 and N2 selectivity reaching about 80 % and 100 %, respectively. EPR, NH3-TPD and Py-IR analyses revealed that the Mn-Ce interface induces the formation of Lewis acid sites and oxygen vacancies, facilitating the adsorption and conversion of chlorobenzene, NH3, and NO. Mn adjacent to Lewis acid sites is the main active site, while Ce acts as an electron transfer agent. Based on the results of in-situ DRIFTS and TOF-SIMS, the possible degradation pathway for chlorobenzene was proposed and as follows: phenol, benzoquinone, maleic anhydride, propionic acid, CO2, and H2O. The NH3-SCR reaction follows the Eley-Rideal mechanism at 150–300℃.

Sulfonated graphitic carbon catalyst derived from coffee waste: A sustainable valorization approach for highly efficient production of 5-hydroxymethylfurfural (5-HMF) from fructose

According to recent research, a sulfonated 2D graphitic carbon catalyst for the dehydration of fructose to the platform chemical 5-Hydroxymethylfurfural (5-HMF) can be made from used ground coffee. By carbonizing and activating at different temperatures, sulfonated graphitic carbon (SC) catalysts with varied chemical compositions and textural characteristics were obtained. The physical and chemical characteristics of the SC catalysts were assessed using XRD, Raman, SEM-EDX, HR-TEM, BET analysis, and XPS. Due to its microporous structure, SC-900 exhibited a high specific area and demonstrated selective and efficient production of 5-HMF from fructose. All in all, the surface acidity of catalysts was measured by NH3-TPD, and acid-base titration methods. The SC-900 catalyst, designed through carbonization at 900 ℃, achieved a fructose conversion rate of 100 % and a 5-HMF yield of 97.91 % without generating any by-products. This indicates the catalyst essentially produces 5-HMF under the specified optimal conditions (140 ℃, 90 min) observed in this study. To determine the origins of the highly efficient and highly selective conversion of fructose to 5-HMF, the performance of the SC catalysts was systematically investigated vi-a-vis their physical and chemical properties. The development of microporous SC catalysts and their application as catalysts not only enhances the value of waste coffee but also provides an environmentally friendly approach for converting carbohydrates into 5-HMF.

Insights into the Acidic Site in Manganese Oxide in Terms of the Sulfur and Water Tolerance of Low-Temperature NH3 Selective Catalytic Reduction.

A critical constraint impeding the utilization of Mn-based oxide catalysts in NH3 selective catalytic reduction (NH3-SCR) is their inadequate resistance to water and sulfur. This vulnerability primarily arises from the propensity of SO2 to bind to the acidic site in manganese oxide, resulting in the formation of metal sulfate and leading to the irreversible deactivation of the catalyst. Therefore, gaining a comprehensive understanding of the detrimental impact of SO2 on the acidic sites and elucidating the underlying mechanism of this toxicity are of paramount importance for the effective application of Mn-based catalysts in NH3-SCR. Herein, we strategically modulate the acidity of the manganese oxide catalyst surface through the incorporation of Ce and Nb. Comprehensive analyses, including thermogravimetry, NH3 temperature-programmed desorption, in situ diffused reflectance infrared Fourier transform spectroscopy, and density functional theory calculations, reveal that SO2 exhibits a propensity for adsorption at strongly acidic sites. This mechanistic understanding underscores the pivotal role of surface acidity in governing the sulfur resistance of manganese oxide.

Thermal stable Pt clusters anchored by K/TiO2–Al2O3 for efficient cycloalkane dehydrogenation

Catalytic dehydrogenation of cycloalkanes is considered a valuable endothermic process for alleviating the thermal barrier issue of hypersonic vehicles. However, conventional Pt-based catalysts often face the severe problem of metal sintering under high-temperature conditions. Herein, we develop an efficient K2CO3-modified Pt/TiO2–Al2O3 (K–Pt/TA) for cycloalkane dehydrogenation. The optimized K–Pt/TA showed a high specific activity above 27.9 mol·mol−1·s−1(H2/Pt), with toluene selectivity above 90.0% at 600 °C with a high weight hourly space velocity of 266.4 h−1. The introduction of alkali metal ions could generate titanate layers after high-temperature hydrogen reduction treatment, which promotes the generation of oxygen vacancy defects to anchored Pt clusters. In addition, the titanate layers could weaken the surface acidity of catalysts and inhibit side reactions, including pyrolysis, polymerization, and isomerization reactions. Thus, this work provides a modification method to develop efficient and stable dehydrogenation catalysts under high-temperature conditions.

Tailoring the surface acidity of catalyst to enhance nonthermal plasma-assisted ammonia synthesis rates

We report nonthermal plasma-assisted catalytic ammonia synthesis from N2 and H2 molecules at near ambient conditions in a custom-built coaxial dielectric barrier discharge plasma reactor. Here, we strategically designed catalysts to facilitate dissociation of strong nitrogen bond and desorption of NH3 molecules. This work demonstrates the use of empty orbitals of boron doped in graphitic carbon nitride (BCN) to activate nitrogen molecules, by creating electron-deficient sites, under nonthermal plasma conditions. Transition metals (Co and Fe) further contribute to the ammonia generation by altering the amount of weak acid sites of the BCN catalyst. As a result, at 20.16 kJ L−1, the maximum ammonia synthesis rate of ∼2.48mmolg−1h−1 was achieved by Co-BCN that corresponds to energy efficiency of 2.09 g-NH3 kWh−1, which was ca. 2.89-folds higher than that of plasma only. Evidently, dual mechanisms at play, leading to enhanced ammonia synthesis rates. Our strategy of tailoring catalyst structure provides a roadmap for engineering synergy with nonthermal plasma towards targeted applications.

Ni Nanoparticles Supported Montmorillonite Clay for Selective Catalytic Transfer Hydrodeoxygenation of Vanillin into 2‐Methoxy‐4‐methylphenol

AbstractThe targeted catalytic transfer hydrodeoxygenation (CTHDO) of vanillin (VAN) to 2‐methoxy‐4‐methylphenol (MMP) holds promise as a noteworthy subject in the domain of bio‐oil utilization, offering potential as a future biofuel and finding versatile use in fragrances and pharmaceutical industry. In this study, stable, cost‐effective Ni nanoparticles supported on montmorillonite (MMT) clay was synthesized for eco‐friendly, alcohol‐mediated CTHDO of VAN to MMP. The Ni(10 %)/MMT catalyst achieved >99 % VAN conversion and 95.2 % MMP selectivity using isopropanol (IPA) as a solvent and hydrogen donor. Characterization encompassing PXRD, SEM, TEM, and XPS confirmed successful Ni integration onto MMT. NH3‐TPD, pyridine‐IR, and H2‐TPR analysis evaluated catalyst surface acidity and reducibility. The synergy between surface‐modulated acidity of MMT and Ni nanoparticles collectively facilitated IPA and VAN activation, driving CTHDO performance. The Ni(10 %)/MMT catalyst displayed sustained activity over five recycles. Its exceptional stability and performance underscore its potential as an eco‐friendly, sustainable, non‐noble transition metal‐based catalyst for the hydrogenating lignin bio‐oil model compounds, contributing to greener catalytic advancements.

Co–Fe catalyst supported on acidified bentonite for selective hydrogenation of cinnamaldehyde

Acidified bentonite supported Co and Fe catalyst (Co–Fe/ACBT) with abundant strong Lewis acid sites was used for cinnamaldehyde selective hydrogenation, which showed a great catalytic activity with 90.5% CAL conversion and 86.8% COL selectivity.

The facilitating effect of sulfide treatment coupled sol-gel method on NH3-SCR activity of Fe–Mn/TiO2 catalysts

The 5Fe–3Mn–S/TiO2-SG catalysts were synthesized by sulfide treatment coupled sol-gel method to develop new NH3-SCR catalysts with wide temperature window, good low-temperature activity and environment-friendly. The evolution of catalyst surface chemical state, morphology, structure, acidity and interaction forces were systematically investigated by XPS, BET, XRD, SEM, H2-TPR, NH3-TPD, UV, IR and steady-state kinetic tests. The influence of sulfide treatment coupled sol-gel method on NO conversion was explored. XRD, BET and SEM characterization revealed that sulfide treatment resulted in smaller catalyst particles and higher dispersion, which increased the specific surface area. XPS, NH3-TPD and steady-state kinetic tests results demonstrated that the sulfide treatment catalysts had a higher surface adsorbed oxygen (Oα) content, which could produce more oxygen vacancies on the catalyst surface, thus increasing the number of acid sites. H2-TPR and UV results demonstrated that the 5Fe–3Mn–S/TiO2-SG catalysts exhibited the strongest contact between the carrier and the active component. The 5Fe–3Mn–S/TiO2-SG catalyst obtained more than 80% NO conversion in the operational temperature range of 220–420 °C, according to the NH3-SCR reaction data. The temperature window was expanded by 120 °C compared to conventional Fe–Mn/TiO2 catalysts, and 98% conversion was achieved at 300 °C. Meanwhile, DFT calculations of the SO42--MnFe2O4(311) crystalline surface of the 5Fe–3Mn–S/TiO2-SG catalysts revealed that it could form stronger chemisorption for both NH3 and NO, which promoted the NH3-SCR reaction more effectively. The DFT calculation results and the experimental findings agreed well.

Regeneration of PbO-deactivated Mn-Ce/Ti-bearing blast furnace slag SCR catalyst: Washing and Mn-Ce reloading

The NH3-SCR of NOx from sintering flue gas can be hindered by PbO, deactivating catalysts and making its regeneration a significant challenge. To address this issue, a novel MnOx-CeO2/Ti-bearing blast furnace slag catalyst was developed and its Pb poisoning mechanism was previously elucidated. In this work, regeneration of Pb-poisoned catalyst was systematically evaluated, including washing with different agents and replenishing MnOx-CeO2 components. The optimal conditions for catalyst cleaning were 1.5 mol/L H2SO4 pickling at 30 °C for 2 h. The doped SO42− could interact with catalyst ingredients, generating sulfate substances that partly transformed into various active sulfur-bearing species. These species enriched the catalyst surface and led to the formation of new S-OH/S = O chemical bonds. Loading MnOx-CeO2 further improved the catalyst's redox capacity by facilitating electronic conversions and increasing chemisorbed oxygen Oα content. The regeneration process also enhanced catalyst surface acidity by generating new N = O and N-OH bonds (N = Mn, Ce), intensifying the adsorption and activation of gaseous NH3. The present work offers new insights into the regeneration of MnOx-CeO2/Ti-bearing blast furnace slag catalyst, particularly for their application in flue gas streams with high Pb content.

Mechanistic insight into reaction behaviors of acetonitrile catalytic combustion over Cu-based catalysts with different supports

A series of Cu-based catalysts with different types of supports (TiO2, Al2O3, S-1, HZSM-5 SiO2/Al2O3 =27 and 85) were investigated for selective catalytic combustion of acetonitrile (CH3CN). Among all catalysts, the Cu/TiO2 and Cu/Al2O3 catalysts had superior activity accompanied with the generation of massive NOx, while Cu/ZSM-5 catalysts exhibited excellent N2 selectivity. The characterization results indicated that the surface acidity of catalysts played a decisive role in reaction behavior. For the Cu/TiO2 and Cu/Al2O3 catalysts mainly with Lewis acid sites, CH3CN underwent an initial hydrolysis step with surface hydroxy group to form acetamide anion (CH3CONHad), then occurred further hydrolysis reaction to form NH3 at low temperatures, or turned to proceed oxidation reaction with numerous NOx generation at high temperatures. Whereas, the enriched Brønsted acid sites on the Cu/ZSM-5 catalysts brought abundant isolated Cu2+ ions, which guaranteed the processing of iSCR reaction, thereby promoting the occurrence of hydrolysis and oxidation reaction pathways in parallel and benefiting the improvement of N2 selectivity. These results elucidated the influence of supports with different acidic types in reaction pathway and provided precious reference for the development of high-performance NVOCs catalysts.

Realizing Influence of Supports in Aqueous‐Phase Hydrogenation of Furfural over Nickel Catalysts

AbstractThe catalytic activity of nickel nanoparticles (5% Ni w/w loading) dispersed on different metal oxide supports has been explored for the hydrogenation of furfural. Nickel, supported on reducible oxides (CeO2 and TiO2), displays higher (almost 100%) conversion compared to that on non‐reducible oxide supports (SiO2, Al2O3, Mg3AlOx). H2‐TPR and XPS analyses bring out the influence of metal‐support interaction during the reduction of nickel precursor and their electronic properties. The adsorption and activation of furfural on the catalyst has been studied using infrared spectra and DFT calculations. The reaction proceeds via both ring‐rearrangement and ring hydrogenation pathways, with furfuryl alcohol as the primary intermediate. At higher reaction temperature, reducible oxide supported catalysts, particularly titania, favours deep‐hydrogenated products and higher conversion than non‐reducible oxide supported catalysts. Among all the catalysts, nickel on titania displayed maximum conversion of furfural. TiO2 possessing higher acidity than ceria, favoured ring‐rearrangement of furfuryl alcohol to cyclopentanone at high temperatures, while the latter retarded reduction of cyclopentanone due to blockage of active‐sites by unreacted furfural and strongly adsorbing intermediates. The combined effects of the electronic‐state of supported metal and surface acidity of catalyst provide a new strategy to tune catalytic properties for selective transformation during hydrogenation of furfural.

Poisoning mechanism of different Cd precursors on Fe-Ce/TiO2 catalyst for selective catalytic reduction of NOx with NH3

As one of the most harmful heavy metals, Cd can present in many chemical forms in real flue gas and may deactivate the SCR catalysts, but the poisoning mechanism of different Cd species over the Fe-Ce/TiO2 catalysts remains unclear. Therefore, in our work, Fe-Ce/TiO2 catalyst is prepared and doped with Cd(NO3)2, CdCl2, and CdSO4, respectively, aiming to investigate the effect of different Cd precursors on the catalytic performance, physicochemical properties, and poisoning mechanisms of Fe-Ce/TiO2 catalyst. The results demonstrate that different Cd precursors exert different influences on the catalytic activity of the catalyst and the deactivation sequence is CdSO4 <Cd(NO3)2 <CdCl2. The doping of Cd decreases the specific surface area, promotes the grain growth of active species, and results in the aggregation of surface active species to varying degrees. Although the total H2 consumption of Cd poisoned catalysts is enhanced, they are not originated from more amounts of surface active species and thus it does not contribute to the redox cycles and catalytic activity of catalysts. The doping of Cd(NO3)2 decreases the surface acidity of catalysts, while CdCl2 and CdSO4 promote surface acidity, but the adsorbed NH3 over CdCl2 poisoned catalyst is unreactive. In addition, both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms are involved in the SCR reaction over the Fe-Ce/TiO2 catalyst and different Cd poisoning makes no change to the reaction mechanism.

Design and identify the confinement effect of active site position on catalytic performance for selective catalytic reduction of NO with NH3 at low temperature

In heterogeneous catalysis, the migration and aggregation of active nanoparticles has always been a challenging problem in catalyst design. Two types of confined catalysts, including the pore confined Pore-CeW/OMT and framework confined FW-CeW/OMT were successfully designed for NH3-SCR process in this work. Experimental results revealed that the framework confined structure could effectively prevent the migration and aggregation of highly dispersed nanoparticles on catalyst. Benefiting from the structural advantages of ordered mesopores TiO2 (OMT), large specific surface area as well as abundant active sites could be supplied for catalytic reaction. It should be noted that citric acid pretreatment was essential for confined catalyst activation. The activation treatment could dramatically enhance catalyst surface acidity, especially a large number of strong acid sites were supplemented, resulting in significantly enhancement of catalytic activity at high temperature. Furthermore, it could also accelerate reduction of Ce4+ to Ce3+ and generate more active oxygen species, which resulted in a significant improvement in its low-temperature catalytic activity. Owning with strong surface acidity as well as framework confinement effect, the unique ordered mesoporous TiO2 framework could inhibit SO2 adsorption and protect active sites from SO2 attacking. Thus, the framework confined FW-CeW/OMT exhibited wide operating temperature window, good thermal stability, as well as strong sulfur resistance in NH3-SCR process.

Bifunctional catalyst of CuMn-HZSM-5 for selective catalytic reduction of NO and CO oxidation under oxygen atmosphere

Simultaneous removal of NOx and CO from steel sintering has attracted great attention because it is difficult to balance the catalyst reducibility and surface acidity merely using metal oxides or zeolite catalysts. In this study, a mixed CuMn-HZSM-5 catalyst was prepared via an impregnation method. The optimized sample exhibited excellent performance with 90% NO conversion and 100% CO conversion at 175 °C. The activity window of the catalyst was coincident with the actual demand of sintering flue gas control at 150-250℃. The active component CuMn suppressed the excessive Lewis acid sites on the zeolite support for NH3 adsorption, while the reducibility of the catalyst also decreased compared with that of pure CuMn metal oxides. This synergistic effect was beneficial for the reduction of NH3 nonselective oxidation with O2. In addition, both the DFT and DRIFTS results revealed that NO conversion was improved by CO introduction at low temperature, since NO could adsorb on the CO-preadsorbed sites for the reduction to N2 via the O atoms of Mn3c sites, i.e., adsorbed CO could also serve as a reductant to reduce NO to N2, which provides another reaction pathway in SCR reactions. Moreover, the NO2− and N2O2− species were observed in the spectra as key intermediates to oxidize CO to CO2, which are also the promoters for CO control.

Promoting catalytic performance by balancing acid and redox sites on Mn3O4–Mn2P2O7/TiO2 for selective catalytic reduction of NO by NH3 at low temperature

The surface acidity and redox property of catalyst are extremely important in the selective catalytic reduction of NOx with NH3 (NH3-SCR) process. In this work, phosphoric acid was used to regulate the acidity and redox property of Mn3O4/TiO2 and Mn3O4–Mn2P2O7/TiO2 (MnPO/TiO2) catalyst was firstly prepared. And its effect on the catalytic activity was investigated in NH3-SCR. The experimental results showed that Mn2P2O7 modified Mn3O4/TiO2 catalyst exhibited excellent catalytic activity and strong resistance to SO2 and H2O than Mn3O4/TiO2. The Brunauer-Emmett-Teller (BET) results showed that the formation of Mn2P2O7 was beneficial to optimize pore structure and significantly increased the specific surface area of Mn3O4/TiO2 catalyst. At the same time, the generation of Mn2P2O7 led to partial obstruction of Mn3+/Mn4+ with Mn2+ redox cycles, which weakened the redox property of Mn3O4/TiO2 catalyst and then prevented excessive dehydrogenation of NH3. Furthermore, the introduction of Mn2P2O7 provided more acid sites for Mn3O4/TiO2 catalyst. The moderate redox property and enhanced acidity facilitated adsorption and activation of NO and NH3. In situ DRIFTs results showed that the SCR reaction over MnPO/TiO2 catalyst at 200 °C was predominantly controlled by L-H route.