Surface Acidity Research Articles

Revealing insights into the unexpected effects of ZnO on selective catalytic reduction (SCR) activity of the CeOx-WO3 catalyst

This study delved into the intriguing impact of zinc oxide (ZnO) on the selective catalytic reduction (SCR) performance of a CeOx-WO3 catalyst with a Ce/W molar ratio of 3:2 (denoted as CW). The introduction of ZnO, at low concentrations of 1 wt% or 3 wt%, resulted in a diminution of the catalyst’s surface acid sites, which hampered the adsorption of NH3 and negated the benefits of improved NH3 activation due to the enhanced oxidative capacity. Consequently, the proceeding of the SCR reactions was significantly impeded, with a marked decrease in NOx conversion to approximately 42 % at 200 °C, which was nearly half that of the virgin CW catalyst. In contrast, increasing ZnO loading to 5 wt% facilitated the formation of ZnWO4, which introduced additional strong acid sites and bolstered NH3 adsorption at moderate and high temperatures. This, in conjunction with the heightened reactivity of surface Ce4+, resulted in a resurgence of deNOx performance, with a NOx conversion increase of ∼ 13 % at 250 °C compared to the catalyst with 3 wt% ZnO. Conversely, escalating ZnO loading to 7 wt% disrupted the formation of ZnWO4 and the excess ZnO neutralized the catalyst’s acid sites, thereby hindering NH3 adsorption and reducing NOx conversion. These insights were instrumental for the prospective application of the CeOx-WO3 catalysts under heavy metal-rich conditions.

Achieving Ultra-Low-Sulfur Model Diesel Through Defective Keggin-Type Heteropolyoxometalate Catalysts

Various Keggin-type heteropolyoxometalate catalysts with structural defects and surface acidity were synthesized by immobilizing 12-phosphotungstic acid (HPW) on mesoporous SBA−15, to produce near-zero-sulfur diesel fuel. As the calcination temperature increased, the W=O and the corner-shared W–O–W bonds in the Keggin unit partially broke, creating oxygen defects, as evidenced by the Rietveld refinement and in situ FTIR characterization. All the catalysts contained Lewis (L) and Brønsted (B) acid sites, with L acidity predominant. The relative intensity of the IR band (I980) of W=O bond inversely correlated with the number of L acid sites as the calcination temperature varied, suggesting that oxygen defects contributed to the Lewis acid sites formation. In the oxidation of dibenzothiophene (DBT) in a model diesel within a biphasic system, DBT conversion exceeded 99% under the optimal reaction conditions (reaction temperature 70 °C, reaction time 60 min, H2O2/sulfur molar ratio 8, H2O2/formic acid molar ratio 1.5, catalyst concentration 2 mg/mL). The influence of fuel composition and addition of indole and 4,6-DMDBT on DBT oxidation were also evaluated. Indole and cyclohexene negatively impacted the DBT oxidative removal. Oxygen defects served as active centers for competitive adsorption of sulfur compound and oxidant. Both L and B acid sites were involved in transferring O atom from peroxophosphotungstate complex to sulfur in DBT, resulting in DBTO2 sulfone, which was immediately extracted by polar acetonitrile. This study confirms that structural defects and surface acidity are crucial in the deep oxidative desulfurization (ODS) reaction, and in enabling the simultaneous oxidation and separation of refractory organosulfur compounds in a highly efficient model diesel.

Zirconium Phosphates and Phosphonates: Applications in Catalysis

This review covers recent advancements in the use of zirconium phosphates and phosphonates (ZrPs) as catalysts or catalyst supports for a variety of reactions, including biomass conversion, acid–base catalysis, hydrogenation, oxidation, and C-C coupling reactions, from 2015 to the present. The discussion emphasizes the intrinsic catalytic properties of ZrPs, focusing on how surface acidity, hydrophobic/hydrophilic balance, textural properties, and particle morphology influence their catalytic performance across various reactions. Additionally, this review thoroughly examines the use of ZrPs as supports for catalytic species, ranging from organometallic complexes and metal ions to noble metals and metal oxide nanoparticles. In these applications, ZrPs not only enhance the dispersion and stabilization of active catalytic species but also facilitate their recovery and reuse due to their robust immobilization on the solid support. This dual functionality underscores the importance of ZrPs in promoting efficient, selective, and sustainable catalytic processes, making them essential to the advancement of green chemistry.

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.

Soluble Polyimide Coated UHMWPE Fibers with Multiple Property Enhancements: Surface Activity, Tensile Strength, Heat Resistance, Acid Resistance, and Erasability.

Ultrahigh molecular weight polyethylene (UHMWPE) fibers possess excellent mechanical properties, yet their applications are severely limited by surface inertness and low melting points. To enhance surface activity and temperature resistance, soluble polyimide (PI) is applied to the surface of UHMWPE fibers. A mussel-inspired biomimetic polycatechol/polyamine (PA) coating is initially constructed on the UHMWPE fiber surface by oxidative self-polymerization, serving as a secondary reaction platform. Subsequently, multifunctional UHMWPE-PA-PI fibers are prepared by depositing soluble PI on the fiber surface via impregnation. The PA and PI layers are firmly bonded by hydrogen bonding interactions and physical adhesion. The results show that the PI-coated UHMWPE fiber surface exhibits enhanced chemical activity, hydrophilicity, and thermal stability, with an increased thermal decomposition temperature of approximately 30 °C. Compared to pristine UHMWPE, the breaking force of UHMWPE-PA-PI fibers increases by 14.9%, and the interfacial adhesion strength between the fiber and rubber improves by 65.5%. The PI coatings also provide thermal insulation, acid resistance, and erasability functionalities. This modification strategy is highly efficient, simple, and less damaging, offering a novel solution to address UHMWPE fibers' surface inertness and temperature intolerance.

Promising metal-free green heterogeneous catalyst for quinoline synthesis using Brønsted acid functionalized g-C3N4

Rationally designing distinct acidic and basic sites can greatly enhance performance and deepen our understanding of reaction mechanisms. In our current investigation, we studied the utilization of Brønsted acid sites within layered graphitic carbon nitride (g-C3N4) for the first time to enhance the rate of the Friedländer synthesis. The structural and surface analyses confirm the effective integration of -COOH and -SO3H groups into the g-C3N4 lattice. The surface-functionalized g-C3N4-CO-(CH2)3-SO3H exhibits a remarkable acceleration in quinoline formation, surpassing previously mentioned catalysts, and demonstrating notable recyclability under optimized mild reaction conditions. The heightened reaction rate observed over g-C3N4-CO-(CH2)3-SO3H is attributed to its elevated surface acidity. By probing the Friedländer reaction mechanism through surface characterization, examination of reaction intermediates, and investigation of substrate scope, we elucidate the pivotal role of Brønsted acid sites. This study constitutes a comprehensive exploration of metal-free heterogeneous catalysts for the Friedländer reaction, offering a unique contribution to the field.

Enhanced Regulation of Selectivity by the Coupling Effects of Surface Acidity and Strain Effects via Precisely Controlling the Location of Pt.

Loading a sensitizer and constructing a rational nanostructure have been reported to be effective approaches for enhancing the catalytic/sensing performance. However, the impact of the precise loading position on the catalytic/sensing performance is always overlooked. Here, we discovered that precisely changing the location of Pt clusters from the outside of Al2O3-ZnO nanocoils (O-PtAlZnNCs) to the inner side of the nanocoils (I-PtAlZnNCs) could change the sensing performance of the sensor from H2S to acetone. Furthermore, precisely loading Pt inside of the confined space led to a high sensing performance and reduced the limit of detection (LOD) of acetone by a factor of 50 times (from 100 to 2 ppb). Combining X-ray photoelectron spectroscopy (XPS), NH3-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ X-ray absorption spectroscopy (XAS), and density functional theory (DFT) simulations, the enhancement of sensitivity and regulation of sensing selectivity are attributed to the coupling effects from enrichment of confined space and Al2O3 acid-base active sites as well as the regulation of electronic structure by location-dominated strain effects. This work not only provides a novel sight to precisely regulate the selectivity and obtain ultrasensitive materials but also serves as a useful instruction for further understanding and precisely designing specific sensors and catalysts with high performance.

Improved catalytic NO oxidation over Pt supported on sulfuric acid treated TiO2

Promoting the formation of metallic Pt over the catalysts is the key to improving the NO reactivity. In general, TiO2 suppresses the oxidation of Pt by surface acidity and induces the formation of the metallic phase of Pt by Pt-Ti interaction. However, the limited number of acidic sites (–OH) contributes to the formation of large Pt particles, which may lead to the formation of Pt2+ or Pt4+, resulting in performance degradation. In this study, we further formulated the acidic sites of the TiO2 with sulfuric acid treatment (SA-TiO2) to improve catalytic NO oxidation. During the SA treatment, the TiO2 surface is positively charged by the low pH, providing an environment for well-distributed sulfate. In the subsequent introduction of Pt, the increase in acidic sites for Pt adsorption greatly enhanced the dispersion of Pt. During this process, Pt formed bonds with sulfate as [Pt(NH3)4]-SO4. The surface species combined with SO4 and NH3 were decomposed during the calcination process, thereby inhibiting the oxidation of Pt, which promotes the formation of metallic Pt. As a result, highly reactive Pt0 and Pt2+ were further formulated by increasing the acidic sites of SA-TiO2, where the low-temperature NO oxidation performance was improved, regardless of the Pt loading (0.3 to 3 wt.%).

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.

Synthesis of low-temperature NH3-SCR catalysts for MnOx with high SO2 resistance using redox-precipitation method with mixed manganese sources

It remains a big challenge to enhance the SO2 resistance of catalyst in low-temperature NH3-SCR reduction. In this work, a series of MnOx-a%Mn (a = 0, 1, 3, 5, 10) catalysts were prepared by introducing manganese acetylacetonate during the reaction between lactic acid and KMnO4, based on the molar ratio of manganese acetylacetonate to KMnO4. Notably, MnOx-5 %Mn exhibited more than 95 % NO conversion and 100 % N2 selectivity at 80–240 °C. Moreover, the catalyst demonstrated excellent sulfur resistance by sustaining over 90 % NO conversion at 140 °C at the presence of 100 ppm SO2 for more than 6 h. Furthermore, XPS characterization indicated that adding manganese acetylacetonate enhanced electron transfer efficiency and improved the reduction capacity of the catalyst due to the interconversion between Mn3+ and Mn4+, which improved electron transfer efficiency. The enhanced reduction capacity of the catalyst promoted the formation of oxygen vacancies and surface-adsorbed oxygen species (Oα), avoiding over-oxidation of NH3. The results elucidated that manganese acetylacetonate could optimize the overall performance by modulating the synergistic effect between the oxidizing ability and surface acidity of the catalyst. Therefore, the MnOx-5 %Mn catalyst possessed a broad operational temperature window (40–240 °C) and SO2 resistance in the NH3-SCR reaction, indicating its potential for practical application.

Improved surface acidity of CeO2/TiO2 catalyst by Cu doping to enhance the SCR catalytic activity

The catalyst is based on CeO2 cannot be widely used in SCR reaction because of its poor NH3 adsorption performance. In this study, Cu-doped CeTi catalyst was designed. The results show that the CeTiCu0.3 has a wide active temperature window of 200–450 °C in NH3-SCR reaction, and NO conversion is > 80%. This is mainly due to the fact that Cu doping provides more acidic sites on the surface of CeTi catalyst, especially the increase of Lewis acid sites is more obvious. NH3-TPD showed that CeTiCu0.3 had a large NH3 adsorption capacity and was mainly adsorbed at Lewis acid sites. In situ DRIFTs results show that NH3 first adsorbs on the Lewis acid site of catalyst in coordination state and reacts with gaseous NOx, while NOx adsorbed on catalyst surface has low reactivity. Therefore, the CeTiCu0.3 catalyst is mainly controlled by the Eley–Rideal mechanism. More Lewis acid sites, and abunda nt Cu2+/Cu+ and Ce4+/Ce3+ formed Cu2+, Ce3+ and surface reactive oxygen species are the main reasons for the excellent catalytic performance of CeTiCu.

Mechanistic investigation of the suppressed N2O formation during the low-temperature NH3-SCR over the Sb-modified Mn/Ti catalyst

The formation of N2O during the NH3-SCR reaction over the Mn-based is one of the crucial factors limiting the industrial application of Mn-based catalysts. In this work, the Sb-modified Mn/Ti catalyst was prepared by the ultrasonic assistance impregnation method to control the formation of N2O during the NH3-SCR reaction. The preferred Mn3Sb/Ti catalyst had over 80 % NOx conversion at 150–300 °C, and more than 80 % N2selectivity at 150–250 °C, which were higher than that of the Mn/Ti catalyst at the same temperature window. A series of performance experiments showed that the Sb modification inhibited the oxidation of NH3to N2O and suppressed the N2O produced by the E-R mechanism in the NSCR reaction, which is the main pathway for N2O generation. Moreover, the presence of NO inhibited the oxidation of NH3 to generate N2O over the Mn3Sb/Ti catalyst. Based on the physical–chemical characterizations and DFT calculations, it was revealed that the introduced Sb species achieves a trade-off between redox ability and surface acidity over the Mn3Sb/Ti catalyst, which is beneficial to enhance the NH3-SCR performance and simultaneously suppress the over-oxidation of NH3. The high content of Mn3+caused by the electron transfer through the redox cycle of Sb3++Mn4+→Sb5++Mn3+ was beneficial in decreasing the N2O formation.The formation of NH speciesis inhibited on the Mn3Sb/Ti catalyst with a higher energy barrier of the NH2* conversion to NH* species due to the Sb modification. Meanwhile, the energy barrier of NH3*→NH2* is decreased and the energy barrier of NH2*+NO → N2 + H2O is lower than that of NH2*→NH* over the Sb-modified catalyst, indicating that the NH3-SCR reaction is more favorable than the formation of N2O on the Mn3Sb/Ti catalyst.

Functionalized construction of multiple active centers for durability controlling during catalytic combustion of chlorinated aromatic hydrocarbons

The catalytic combustion of chlorine-containing VOCs primarily encounters the bottleneck of catalyst poisoning by chlorine, thereby impeding the further industrial application of this technology. The development of multi-active catalytic materials for discerning chlorine fixation, chlorine transfer, deep oxidation during elimination of chlorine-containing VOCs can mitigate catalyst chlorination and enhance stability. Herein, we utilizing LDHs as catalyst precursors and successfully synthesized flower-like Co2FexCr1-xOy catalyst with different functionalized reaction centers. The addition of Cr improved the surface lattice oxygen, oxygen vacancies, and acid sites of catalyst. The removal efficiency of CB can be achieved >90 % at 247 °C (WHSV = 33000 mL · g−1·h−1). The fixation of dissociated chlorine contributed by Cr not only enhances oxidation performance and directional adsorption of chlorine, but also improves carbon deposition resistance and catalyst sintering resistance significantly. Compared with Co2Fe1Oy, Co2Fe0.67Cr0.33Oy catalyst achieves a remarkable threefold reduction in surface carbon deposition. The DFT calculation revealed that water dissociation energy over the Co site is −0.72 eV, which is significantly lower than Fe (−0.59 eV) and Cr (−0.17 eV), facilitating water dissociation and subsequently removes a substantial amount of accumulated chlorine on Cr to form HCl. With the help of In situ DRIFT and GC/MS analysis, we found the efficient removal of chlorine atoms enhances the exposure of active sites on the catalyst surface with hydrolyzed hydroxyl group, which facilitating the conversion of aromatic hydrocarbons into a greater quantity of maleate and carboxylate species. This phenomenon is beneficial for the subsequent mineralization process of chlorobenzene. This work provide valuable insights for multi-active site catalysis mechanism in practical applications aimed at eliminating chlorinated organic waste gases from industrial emissions.

Enhanced microwave-catalytic performance for CO2 oxidative propane dehydrogenation by acidified and Bi-doped ZnO-based microwave catalysts

The oxidative dehydrogenation of propane by carbon dioxide (CO2-ODHP) has great potential in producing propylene. Resource utilization of CO2 will be the dominant trend in the future to mitigate environmental problems and cope with the growth in energy demand. However, simultaneously achieving high propane conversion, high propylene selectivity, and high CO2 conversion at low temperatures remains challenging. Herein, we report a novel efficient microwave catalyst (1.0-Zn4Bi1/Silicalite-1+SiC) by doping Bi on ZnO/Silicalite-1 and then acid treatment. The (1.0)-Zn4Bi1/Silicalite-1+SiC microwave catalyst exhibited 92 % C3H8 conversion, 84 % C3H6 selectivity, and 45 % CO2 conversion under microwave mode, significantly better than under the thermocatalysis (without microwave: 27 % C3H8 conversion, 92 % C3H6 selectivity, and 14 % CO2 conversion). The CO2 capture capacity was improved by adding Bi to ZnO/Silicalite-1. In addition, acid modification increased the propane and CO2 conversion by 1.9 and 1.3 times, respectively. Notably, acid treatment enriched the pore structure of the catalysts, altered surface acidity and alkalinity, and promoted C3H8 and CO2 activation and C3H6 desorption. In particular, the acid treatment enriches the state of the presence of Zn species in the catalyst. Microwave irradiation reduces the apparent activation energy of the catalytic system and accelerates the removal of coke from the catalyst surface. Microwave catalysis can activate CO2 and propane at lower temperatures than thermocatalysis.

Morphology and crystal–plane dependent catalytic activity of α-Fe2O3 for NH3-SCR de-NOx: Experimental and DFT study

Three kinds of α-Fe2O3 catalysts, each having a distinct morphology and crystal planes, were synthesized and applied for NH3-SCR reaction. The morphology and crystal-plane effects for the activity of α-Fe2O3 were investigated by a combined study of experiment and density functional theory. The experiment findings reveal that the α-Fe2O3-S, α-Fe2O3-R, and α-Fe2O3-C display the shuttle (predominantly exposed (110) and (012) crystal planes), rod (predominantly exposed (110), (104), and (012) crystal planes), and cube (only exposed (104) crystal plane) shapes, respectively. Furthermore, the α-Fe2O3-S yields the best catalytic performance because of its moderate surface acidity, the best redox capacity, and the highest contents of surface Fe3+ and chemisorbed oxygen, which may result from the morphology and crystal plane effects. Additionally, the activity of different crystal planes is significantly different. The NO and NH3 are more apt to be adsorbed on the (110) and (012) surfaces and O2 dissociation is more likely to happen on the (110) surface. Besides these, the (110) surface owns the lowest energy barrier to the decomposition of intermediate NH2NO. All of the mentioned above collectively enhance the efficiency of the SCR process. Finally, the (110) and (012) surfaces facilitate the rapid SCR process, while the (104) surface is the most difficult. The α-Fe2O3-S predominately exposes high activity of (110) and (012) surfaces, therefore, it can yield the highest catalytic activity.

Influence of the synthesis route on Au-Ir/Al2O3 catalysts performing the total propane oxidation reaction at low temperature

The current study highlights synthesis as a key parameter for obtaining Au-Ir/Al2O3 bimetallic catalysts using the deposition-precipitation with urea (DPU) method. Both co-deposition and sequential deposition (first by adding Au and then Ir and vice versa) were employed. These approaches were compared with the sol-gel and impregnation methods, revealing notable differences in the catalytic oxidation of C3H8 at low temperatures. The Au-Ir/Al2O3 catalysts prepared via co-deposition and sequential deposition demonstrated outstanding results, producing nanoparticles as small as 1 nm when thermally reduced in hydrogen at 400 °C; also, these catalysts exhibited greater capacity for oxidizing C3H8 below 280°C than the Ir/Al2O3 and Au/Al2O3-based catalysts. Characterization of the catalysts was conducted by employing various techniques, including in-situ DRIFTS, UV-Vis, H2-TPR, HAADF-STEM-EDS, XPS and surface acidity determinations by pyridine thermo-desorption. This last technique showed differences in total acidity (Brönsted and Lewis) provoked by the Au-Ir interaction in the different catalysts, which significantly influenced their ability to oxidize C3H8 towards CO2. The results emphasize the effectiveness of the co-deposition and sequential deposition methods using the DPU approach compared to the sol-gel and impregnation methods.

Noble metal-free tandem catalysis enables efficient upcycling plastic waste into liquid fuel components

The lack of effective approaches for upcycling waste plastic has led to severe environmental pollution and squandering of carbon resources. While hydrocracking macromolecular polyolefins over typical metal-zeolite catalyst produces high quality liquid fuel components, the limited activity of base metal and restricted accessibility of acid sites within microporous zeolite renders this process still not in practical scale. A tandem catalyst comprising Ni-WO3/Al2O3 and Beta zeolite was developed for consecutive hydrocracking polyolefins, achieving a yield of 86.2 % of primarily gasoline-jet ranged hydrocarbons (mainly C5-C16 and minor C16+) at 280 °C. The incorporation of tungsten species onto Ni/Al2O3 largely enhances the surface acidity and accelerates the primary cracking process that converts polyethylene (PE) into medium-sized intermediates, which would readily diffuse into the pore networks of Beta and undergo further cracking to yield desired liquid hydrocarbons. In addition, this tandem catalyst also promotes facile hydrocracking of consumer-grade plastic waste and maintains excellent stability over 5 recycling tests. The noble-metal-free catalyst achieves an impressive liquid formation rate of 5.74 g·gcat.−1·h−1, rivaling the noble metal-based catalyst and demonstrating high application prospects.

Synergistic removal of NO and CO in industrial waste gas by Fe-modified Cu/TiO2 catalysts: The synergistic effect of metal oxides interaction

NH3-based selective catalytic reduction (NH3-SCR) combined with carbon monoxide (CO) catalytic oxidation is a productive way to synergistically remove nitrogen oxides (NOx) and CO from industrial waste gas. Catalyst is the undoubtedly centerpiece of the synergistic removal technology, which has aroused tremendous attention. Herein, in this investigation a variety of Cu/TiO2 catalysts modified by various metal oxides were prepared by impregnation method, and the excellent synergistic removal performance of Fe-modified Cu/TiO2 catalyst was observed. The Cu/TiO2 catalyst with a 7 wt% Fe doping amount exhibited the highest NO and CO removal efficiency (86 % for NO at 300 °C and over 98 % for CO from 300 ∼ 400 °C). Through a series of characterization techniques, it was discovered that Cu and Fe oxides interacted to evenly distribute them throughout the surface of TiO2 support, resulting in smaller particle size and abundant variable valence species (Cu+/Cu2+ and Fe2+/Fe3+) to enhance the redox performance of the catalysts. Moreover, the creation of additional surface chemisorbed oxygen, the adsorption of NO and CO, and the improvement of surface acidity were all facilitated by the electron transfer between various Cu and Fe species. In addition, in-situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTS) results revealed the interaction between NH3-SCR and CO oxidation. This study proposes a viable approach to develop efficient catalysts for the synergistic removal of NO and CO in industrial applications.

In situ decorated Mn-FeOx amorphous oxides on filter felt by a polyphenol-assisted method for low-temperature NH3-SCR

The combination of dust filtration technology and selective catalytic reduction of nitrogen oxides can effectively reduce the energy consumption and footprint of the flue gas purification system. To fabricate the high efficiency and firmly bonded catalytic filter material, a novel polyphenol-assisted method was designed in this work for in situ decorating Mn-FeOx amorphous oxides onto the smooth polyphenylene sulfide (PPS) filter felt. The polyphenolic compounds are not only worked as the dispersant, but also the binder for Mn-FeOx catalysts to firmly anchor on PPS filter felts. The introduction of Fe3+ into catalyst precursors can increase the Mn4+ content, surface adsorbed oxygen, as well as surface acidity, which displays satisfactory denitration performance and SO2 tolerance at low temperatures. The Mn5Fe1-TA/PDA@PPS sample shows nearly 100 % NO conversion efficiency at 180 °C with only 10.11 % catalysts loading in the sulfur dioxide free flue gas. Furthermore, the green and efficient synthesis route makes the catalytic filter felts preserve the same gas permeability and thermal stability with the pristine PPS filter felt, which suggests that the Mn5Fe1-TA/PDA@PPS has great prospects for simultaneously removing of NOx and dust in practical applications.

Highly efficient Fe-Cu/CL catalysts based on low-cost clay minerals for NH3-SCR of NOx at low temperature

One of the main challenges for NH3-SCR of NOx at low temperatures is developing a catalyst with exceptional low-temperature catalytic activity. Herein, four kinds of clay minerals including halloysite (Hte), Ca-montmorillonite (Ca-Mte), chlorite (Cte), and Na-montmorillonite (Na-Mte) were used as supports and impregnated with Fe and Cu to synthesize Fe-Cu/Hte, Fe-Cu/Ca-Mte, Fe-Cu/Cte, and Fe-Cu/Na-Mte catalysts, respectively. Within a temperature range of 180–240 °C, the resultant Fe-Cu/Hte catalyst produced more than 98 % NOx conversion and demonstrated the best low-temperature NH3-SCR catalytic performance. The characterization results indicated that the weakened crystallinity of active species, high ratios of Fe3+/Fe and Cu+/Cu, and more surface absorbed oxygen species, as well as excellent low-temperature redox ability and surface acidity all contributed to its outstanding low-temperature catalytic activity. The in situ DRIFT study at 240 ℃ showed that two forms of the Eley-Rideal (E-R) mechanism existed on the Fe-Cu/Hte and Fe-Cu/Cte catalysts, while the E-R and Langmuir-Hinshelwood (L-H) processes were both involved over the Fe-Cu/Ca-Mte and Fe-Cu/Na-Mte catalysts.