Anti-poisoning Performance Research Articles

Effect of Tourmaline Addition on the Anti-Poisoning Performance of MnCeOx@TiO2 Catalyst for Low-Temperature Selective Catalytic Reduction of NOx.

In view of the flue gas characteristics of cement kilns in China, the development of low-temperature denitrification catalysts with excellent anti-poisoning performance has important theoretical and practical significance. In this work, a series of MnCeOx@TiO2 and tourmaline-containing MnCeOx@TiO2-T catalysts was prepared using a chemical pre-deposition method. It was found that the MnCeOx@TiO2-T2 catalyst (containing 2% tourmaline) exhibited the best low-temperature NH3-selective catalytic reduction (NH3-SCR) performance, yielding 100% NOx conversion at 110 °C and above. When 100-300 ppm SO2 and 10 vol.% H2O were introduced to the reaction, the NOx conversion of the MnCeOx@TiO2-T2 catalyst was still higher than 90% at 170 °C, indicating good anti-poisoning performance. The addition of appropriate amounts of tourmaline can not only preferably expose the active {001} facets of TiO2 but also introduce the acidic SiO2 and Al2O3 components and increase the content of Mn4+ and Oα on the surface of the catalyst, all of which contribute to the enhancement of reaction activity of NH3-SCR and anti-poisoning performance. However, excess amounts of tourmaline led to the formation of dense surface of catalysts that suppressed the exposure of catalytic active sites, giving rise to the decrease in catalytic activity and anti-poisoning capability. Through an in situ DRIFTS study, it was found that the addition of appropriate amounts of tourmaline increased the number of Brønsted acid sites on the catalyst surface, which suppressed the adsorption of SO2 and thus inhibited the deposition of NH4HSO4 and (NH4)2HSO4 on the surface of the catalyst, thereby improving the NH3-SCR performance and anti-poisoning ability of the catalyst.

Theoretical study on the surface poisoning of high-entropy alloys during hydrogen storage cycles: the effect of metal elements and phases.

High-entropy alloys offer promising hydrogen storage properties and design versatility but suffer from compromised capacity and stability in practical industrial applications owing to surface poisoning caused by trace impurities or unexpected contact with air. Theoretical simulations provide a rapid and efficient platform for estimating anti-poisoning performance, particularly concerning alloys versus metal elements in various phases. This work explores the surface poisoning behavior of two typical high entropy materials: BCC-phase V35Ti30Cr25Fe10 and Laves-phase ZrTiVNiCrFe, along with pure metals V, Ti, Cr, and Fe as well as single AB2 (A = Zr, Ti, B = V, Ni, Cr, and Fe) compounds, at various phase stages during hydrogen storage cycles using density functional theory (DFT) simulations. Results show that surfaces of V35Ti30Cr25Fe10 and ZrTiVNiCrFe with a hydrogen uptake of 100% can facilitate O2 adsorption over dissociation, especially when O2 adsorbs on Fe sites, and formation of hydroxyl. The O2 poisoning behavior of high-entropy alloys was roughly estimated using the molar ratio weighted sum of constituent components, with the maximum deviation of 15.92% between predicted values and calculated values. This study sheds light on anti-poisoning mechanisms and aids in designing resilient high-entropy alloys.

Enhancing SCR activity and anti-poisoning of MnOx/m-ZrO2 catalysts by metal doping

This study investigated the impact of metal doping on the DeNOx and anti-poisoning performance of MnOx/m-ZrO2. The DeNOx performance increases from 96% to nearly 100% by Co or Sm doping. However, the anti-poisoning performance was enhanced more by Sm doping, and the DeNOx performance remained at 90.97% after water and sulfur compound poisoning. The improved redox performance caused by the interaction between Sm and Mn resulted in more acidic sites that aid in the adsorption of NOx and NH3, and the presence of Sm effectively inhibits the formation of sulfate and ammonium sulfate, thus enhancing the DeNOx and anti-poisoning performance.

Anti-poisoning performance of flat-tube solid oxide fuel cell in high concentration [formula omitted]S environment

In this work, the anti-poisoning performance of flat-tube solid oxide fuel cells (FT-SOFCs) is investigated in high concentrations of H2S. The degradation rate of the cell is 0.52%/ h, 0.27%/ h and 0.305%/ h at 750 °C, when the concentration of H2S is 161 ppm, 182∼222 ppm and 226 ppm, respectively, and the performance can be restored by humidification of H2. The resistance to sulfur poisoning breaks through the limitation, proving the stability advantage of the flat-tube structure. Through energy dispersive spectrometer (EDS) and Raman spectrum analysis, it is found that the cell performance degradation under high concentration of H2S is mainly caused by the loss of metallic nickel caused by the migration and decomposition of nickel-sulfur compounds, which will reduce the active sites of H2 participating in the anode reaction. This study provides a reference for the application of flat-tube structure cells under high concentrations of H2S.

Coated monolithic catalysts for better selective catalytic reduction: Concerns about structural integrity, catalytic activity and anti-poisoning performance

Coated monolithic catalysts for better selective catalytic reduction: Concerns about structural integrity, catalytic activity and anti-poisoning performance

Promoter not inhibitor: The antidotal effects of arsenic on lead-poisoning V2O5−WO3/TiO2 catalyst for selective catalytic reduction of NOx with NH3

Arsenic has been considered a strong inhibitor for a variety of catalysts for the selective catalytic reduction of NOx with NH3 (NH3−SCR). However, in this work, we found arsenic exhibits a remarkable detoxification effect on lead-poisoning V2O5−WO3/TiO2 catalysts. With only 0.9 wt% arsenic introduction, the NOx conversion over Pb–V2O5−WO3/TiO2 (lead: 2 wt%) could be raised from 35% to 81% at 250 °C under a GHSV of 100,000 h−1. More surprisingly, the negative effect of arsenic on N2 selectivity was greatly inhibited simultaneously. The catalyst characterizations and DFT simulation manifest that arsenic could not only extricate VOx sites and related Lewis acid sites from lead shackles but also promote the redox property through its stronger electronic interaction with the lead. On the basis of in situ DRIFTS and kinetic study, regenerated V=O sites were profitable to the adsorption and activation of NH3 species, thus greatly improving the SCR activity. We demonstrate that the antidotal effect of arsenic to lead poisoning V2O5−WO3/TiO2 catalyst is the increase of active site amount rather than the change of reaction pathway. It is believed that the novel findings above could open up an innovative pathway for toxic heavy metals reduction and catalyst designing with virtuous anti-poisoning performance.

V-Cu bimetallic oxide supported catalysts for synergistic removal of toluene and NOx from coal-fired flue gas: The crucial role of support

It is a major challenge to achieve effective synergistic reduction of NOx and VOCs in coal-fired flue gas under complex working conditions. In this work, V-Cu bimetallic oxide catalysts with different supports were designed. V1-Cu5 bimetallic oxide supported on TiO2 showed significantly higher activity for simultaneous toluene oxidation and NOx reduction than that supported on ZSM-5, SiO2 and γ-Al2O3. Meanwhile, it exhibited excellent stability and anti-poisoning performance, and could block the formation of toxic polycyclic aromatic hydrocarbons in by-products. Compared with ZSM-5, SiO2 and γ-Al2O3, TiO2 as support was conducive to the formation of abundant acidic sites and oxygen vacancies. In addition, the strong interaction between the metal active sites and TiO2 accelerated the electron transfer from Cu to adsorbed O2, thus promoting the formation of active O2−. This work can provide guidance for the development of catalysts designed for the simultaneous catalytic removal of NOx and VOCs.

An anti-poisoning defective catalyst without metal active sites for NH3-SCR via in situ stabilization

The denitrification catalyst without metal active component has excellent anti-poisoning performance and stability.

Enhanced performance and DFT study of sulfur poisoning mechanism of modified Al2O3 catalyst in COS hydrolysis

The sulfur poisoning mechanism of Al2O3 catalysts in COS hydrolysis is still controversial. The modified K0.1Al2O3-PA catalyst exhibited enhanced anti-poisoning performance, which maintained 100 % conversion and 85 % H2S selectivity after 150 h of reaction. The results illustrated that the decrease of activity was related to the reduced specific surface area, basicity, oxygen vacancies and weakened adsorption ability of COS. The sulfur species on the Al2O3 and Al2O3-PA catalyst was Al2(SO4)3 and elemental S, respectively. After adding K, the sulfur species existed stably in the form of K2SO4. The DFT calculation results suggest that the trapping of H2S by K weakens the adsorption of H2S on Al, which protects the Al sites. The results suggested that COS and H2S are difficult to be oxidized by lattice oxygen, especially after adding K. In the presence of O2, H2S is more easily oxidized to generate S and OH– through a two-step dehydrogenation reaction.

A DFT study on adsorption behaviors of NH3 and SO2 on MnCe/TiNTs catalyst

Manganese-cerium catalyst has attracted much attention due to its extraordinarily good low-temperature performance for detrinification technology, but its poor SO2 resistance limits its wide application. A suitable catalyst carrier can enhance the low-temperature activity and anti-poisoning performance of catalyst. In this paper, density functional theory (DFT) was used to construct MnCe catalyst models that supported by conventional TiO2 and TiO2 nanotubes (TiNTs) (denoted as MnCe/TiO2 and MnCe/TiNTs, respectively) to simulate adsorption behaviors of NH3 and SO2 molecules on catalyst surface. The adsorption energies (Eads) of NH3 and SO2 on catalyst surface, projected density of states (PDOS) of surface metal/nonmetal atoms and Mulliken charge were calculated. The results show that NH3 and SO2 molecules prefer to adsorb on top sites of Mn and Ce atoms respectively, but the competitive adsorption between NH3 and SO2 for top site of Ce atom on MnCe/TiO2 surface exists, for their Eads values (-0.42 eV and -0.44 eV) are similar. TiNTs alleviates their competitive adsorption by increasing the adsorption capacity of NH3 and weakening that of SO2 on catalyst surface. It attributes to the fact that TiNTs increases the coordination unsaturation of Mn and Ce atoms that enhances the electron transformation from NH3 molecule to Mn atom and weakens the electron-donating ability of Ce atom to SO2 molecule. In addition, TiNTs own abundant hydroxyl groups (OH) which can act as surface Brønsted acid sites for NH3 adsorption. These facts deeply reveal the promotion mechanism of TiNTs for low-temperature denitrification activity and sulfur poisoning resistance of MnOx-CeO2 catalyst from a microscopic perspective.

Effects of Flue Gas Impurities on the Performance of Rare Earth Denitration Catalysts

Selective catalytic reduction (SCR) is still the most widely used process for controlling NOx gas pollution. Specifically, commercial vanadium-based catalysts have problems such as narrow operating temperature range and environmental pollution. Researchers have developed a series of cerium-based catalysts with good oxygen storage performance and excellent redox performance of CeO2. However, the anti-poisoning performance of the catalyst is the key to its application. There are many kinds of impurities in the flue gas, which has a huge impact on the catalyst. The deposition of substances, the reduction of active sites, the reduction of specific surface area, and the reduction of chemically adsorbed oxygen will affect the denitration activity of the catalyst to varying degrees, and the poisoning mechanism of different impurities on the catalyst is also different. Therefore, this review divides the impurities contained in flue gas into different types such as alkali metals, alkaline earth metals, heavy metals, and non-metals, and summarizes the effects and deactivation mechanisms of various types of impurities on the activity of rare earth catalysts. Finally, we hope that this work can provide a valuable reference for the development and application of NH3-SCR catalysts for rare earth denitration in the field of NOx control.

Diluted silicon promoting Pd/Pt catalysts for oxygen reduction reaction with strong anti-poisoning effect

Poisoning species, such as methanol and air pollutants, degrade the electrocatalytic activity for oxygen reduction reaction (ORR). Here, via taking advantage of the varied electronic property of nano-silicon, a versatile strategy is reported for enhancing the catalytic activity and anti-poisoning ability toward ORR by decorating noble metal catalysts with the size-controlled silicon nanoclusters (DS). Consequently, DS-Pd exhibits the enhanced ORR performance with a large halfwave potential of 0.892 V and an onset potential of 1.010 V. More importantly, it also shows enhanced anti-poisoning performance in methanol, NaNO2 and NaHSO3 electrolytes, compared to those of commercial Pt/C and Pd/C catalysts. Mechanism studies reveal that the synergistic effect between Pd and more oxygen-philic and less poison-philic Si nanoclusters largely abbreviate the absorption of poisoning species on the active sites. This strategy also improves the methanol-tolerant performance of Pt based catalysts, providing a versatile strategy for the fabrication of methanol-tolerant ORR catalysts.

Rational design ternary platinum based electrocatalysts for effective methanol oxidation reaction

Exploring effective, durable, and affordable electrocatalysts of methanol oxidation reaction (MOR) is of vital significance for the industrial application of direct methanol fuel cells. Herein, an efficient, general, and expandable method is developed to synthesis two-dimensional (2D) ternary PtBiM nanoplates (NPLs), in which various M (Co, Ni, Cu, Zn, Sn) is severed as the third component to the binary PtBi system. The MOR performance of PtBiM NPLs is entirely investigated, demonstrating that both the MOR activity and durability is enhanced with the introduction of the additional composition. Pt3Bi3Zn NPLs shows much higher MOR activity and stability than that of the PtBi counterparts, not to mention the current advanced PtRu/C and Pt/C catalysts. The prominent performances are attributed to the modulated electronic structure of the surface Pt in PtBi NPLs by the addition of Zn, resulting in a weakened affination between Pt and the adsorbed poisoning species (mainly CO) compared with PtBi NPLs, verified by density functional theory (DFT) calculations. In addition, the absorbed OH can be generated on the surface of Zn atom due to its favorable water activation properties, thus the CO removal on the adjacent Pt atoms is accelerated, further leading to a high activity and anti-poisoning performance of the resulting Pt3Bi3Zn catalyst. This work provides new insights and robust strategy for highly efficient MOR electrocatalyst with extraordinary anti-poisoning performance and stability.

The promoting mechanism of doping Mn, Co, and Ce on gas adsorption property and anti-SO2 oxidation over γ-Fe2O3 (001) surface: A density functional theory study

To improve the deNOx and anti-poisoning performance of γ-Fe2O3 catalyst, the effects of three dopants Mn, Co, and Ce on gas adsorption and SO2 oxidation were investigated by a DFT method. Results show that NH3, NO, O2 can be adsorbed stably on the γ-Fe2O3 (001) surface to form coordinated NH3, nitrosyl, and adsorbed oxygen species, respectively. SO2 and H2O bind to Fe site on the catalyst surface by weak chemisorption. Doped Mn, Co, and Ce atoms simultaneously improve the gas adsorption performance of its own site and the surrounding Fe sites, especially for Ce doping. Furthermore, doping Mn contributes to the oxidation of SO2 to SO3, while doping Co and Ce restrains the formation of SO3, especially doping Ce, which is conducive to sulfur resistance of the catalyst. By comparison, the doping of Ce has more excellent deNOx and anti-poisoning property for the γ-Fe2O3 catalyst, which provides theoretical guidance for the selection of dopant in the subsequent experiments.

Two-dimensional PdMo curved nanosheets for tunable CO2 electrocatalytic reduction to syngas

Summary Syngas (CO/H2) is an essential industrial feedstock. Electroreduction of CO2 to syngas is a desirable solution to energy and environmental challenges. Two-dimensional (2D) nanomaterials have been identified as promising electrocatalysts in CO2 reduction reactions (CO2RRs). Here, we report 2D PdMo curved nanosheets (PdMo CNSs) as the electrocatalyst for efficient, tunable, selective, and stable electroreduction of CO2 to syngas. The H2/CO ratio is tunable from 0.15:1 to 4:1. The current density can be as high as 65.6 mA cm–2 with a H2/CO ratio of 1:1. Density functional theory calculations illustrate that alloying Mo can optimize the electronic structure around Pd and significantly reduce the kinetic energy barrier, thus improving the migration ability of CO∗ and enhancing the anti-poisoning performance of the electrode to achieve more stable CO2 electroreduction. This work offers a strategy for developing new metal-based 2D nanomaterial electrocatalysts for efficient catalysis of CO2 to syngas.

Enhanced anti-poisoning performance against carbon monoxide of LaNi4.7Al0.3 alloy encapsulated in polymethyl methacrylate

LaNi4.7Al0.3 alloy has been applied in hydrogen recovery system due to the favorable absorption and desorption property. Herein, the LaNi4.7Al0.3 alloy is encapsulated in polymethyl methacrylate (PMMA) by a simple physical mixing method, and the hydrogen absorption and desorption properties in the hydrogen containing 300 ppm carbon monoxide (CO) are investigated. PMMA can accommodate the powdered alloy particles and prevent the contact of CO and alloy. The hydrogen absorption and desorption kinetics properties in hydrogen gas with 300 ppm CO impurities of the LaNi4.7Al0.3 alloy encapsulated in PMMA matrix are improved. PMMA can be used as a potential material to enhance the anti-poisoning property of hydrogen storage alloys.

An acid-base molecular assembly strategy toward N-doped Mo2C@C nanowires with mesoporous Mo2C cores and ultrathin carbon shells for efficient hydrogen evolution

Molybdenum carbides are promising electrocatalysts for the hydrogen evolution reaction (HER). Rational design of morphology, composition and interfacial structure in Mo2C materials is essential to enhance their HER performance. Herein, an acid-base molecular assembly strategy is demonstrated for the synthesis of novel N-doped Mo2C@C core–shell nanowires (NWs) composed of mesoporous Mo2C cores with interconnected crystalline walls and ultrathin carbon shells. The strong interactions between the two precursors, adenine (Ade) and phosphomolybdic acid (PMA), lead to the formation of inter-molecular hybrid NWs during a hydrothermal process. The subsequent pyrolysis leads to confined growth of crystalline Mo2C NWs with inter-crystal mesopores (5 ~ 10 nm), formation of ultrathin carbon shells (~1.5 nm in thickness), and effective N doping. Such a structure architecture can provide abundant active sites, fast and diverse mass and electron transport paths, as well as stable reaction interfaces. The typical N-doped Mo2C@C NWs exhibit high HER performance with a low overpotential of 136 mV at 10 mA cm−2, a small Tafel slop of 58 mV dec-1, excellent durability and outstanding anti-poisoning performance against CO and H2S gases. Furthermore, the influences of several important factors, including the pyrolysis temperature, hydrothermal temperature and precursor mass ratio, on the morphology, composition and structural configuration of the resulted materials are elucidated and correlated with their HER performance. This work may provide a general strategy for the synthesis of other nanoscale metal carbides for various catalytic applications.

Bidirectional controlling synthesis of branched PdCu nanoalloys for efficient and robust formic acid oxidation electrocatalysis

Through a two-way control of hexadecyl trimethyl ammonium bromide (CTAB) and hydrochloric acid (HCl), the PdCu nanoalloys with branched structures are synthesized in one step by hydrothermal reduction and used as electrocatalysts for formic acid oxidation reaction (FAOR). In this two-way control strategy, the CTAB is used as a structure-oriented surfactant, while a certain amount of HCl is used to control the reaction kinetics for achieving gradual growth of multi-dendritic structures. The characterizations including scanning transmission electron microscope (STEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggest that PdCu nanoalloys with unique multi-dendritic branches have favorable electronic structure and lattice strain for electrocatalyzing the oxidation of formic acid. In specific, among the electrocatalysts with different Pd/Cu ratios, the Pd1Cu1 branched nanoalloys have the largest electrochemically active surface area (ECSA) and the best performance for the FAOR. The catalytic activity of the Pd1Cu1 branched nanoalloys is 2.4 times that of commercial Pd black. After the chronoamperometry test, the Pd1Cu1 branched nanoalloys still maintain their original morphologies and higher current density than that of the commercial Pd black. In addition, in the CO-stripping tests, the initial oxidation potential and the oxidation peak potential of the PdCu branched nanoalloys for CO adsorption are lower than those of commercial Pd balck, evincing their better anti-poisoning performance.

Synthesis of bimetallic PdSn nanoparticle assembly as highly efficient electrocatalyst for ethanol oxidation

The direct ethanol fuel cells are considered as a kind of green portable power sources with high energy density and stable convert efficiency. Alloyed PdM performs highly efficient electrocatalyst for ethanol oxidation reaction. In this study, a facile one-step oil bath method was conducted to synthesize alloyed PdSn nanoparticle (NP) assembly in ethylene glycol solution with the help of cetyltrimethyl-ammonium bromide and L-ascorbic acid. Among various alloyed PdSn NPs, alloyed PdSn-15 NP showed much enhanced current density (2230 mA mg−1) in cyclic voltammetric measurements for ethanol electrooxidation, compared to pure Pd NP (1120 mA mg−1). The former has a lower electron transfer barrier, anti-poisoning performance and better catalytic stability than that of latter, closely relative to its optimized coordination environment and change of d-band center of palladium.

Low temperature performance and sulfur resistance enhancement of Mn-Ce oxides supported on W-modified MWCNT for NH3-SCR removal of NOx

ABSTRACT To eliminate nitrogen oxides (NOx), composite carrier-supported catalysts (Mn-Ce/MWCNT-W) and traditional catalysts (Mn-Ce/MWCNT and W-Mn-Ce/MWCNT) were prepared using an ultrasonic impregnation method that preformed low-temperature ammonia-selective catalytic reduction (SCR) removal of NOx. The promotion effects of MWCNT-W composite carriers for low temperature SCR activities and SO2 tolerance of the catalysts were systematically investigated. Compared to traditional catalyst, Mn-Ce/MWCNT-W catalyst, with a 30% WOx/MWCNT mass ratio, demonstrated improved SCR activity and high N2-selectivity from 100°C to 200°C. A series of characterizations were carried out and it was found that there were more redox sites and the stronger the NH3 adsorption capacity over the composite carrier-supported catalysts than traditional catalysts. Also, with this composite carrier-supported catalyst, the improvement of SCR reaction was considered to be from the abundance of high valence state Mn and well dispersed active components. Notably, compared to traditional catalyst, the composite carrier-supported catalyst exhibited the stronger sulfur resistance. Thus, using MWCNT-W composite carriers to prepare Mn-Ce/MWCNT-W catalysts resulted in excellent NOx conversion and SO2 resistance at low temperatures. Implications: LT NH3-SCR of NOx is an effective way to remove NOx from stationary sources. The physicochemical properties of the support not only affect a catalyst’s LT SCR activity but also affect the catalyst’s anti-poisoning performance. The modified carriers could promote active component dispersion, which is conducive to SCR reaction. However, for LT SCR reactions, few reports have addressed the design and preparation of composite carrier-supported catalysts. The goal of this study was to design and synthesize Mn-Ce/MWCNT-W catalysts and to observe the influence of composite support in Mn-based catalysts on LT SCR activity and sulfur resistance.