PdPtVOx/CeO2-ZrO2: Highly efficient catalysts with good sulfur dioxide-poisoning reversibility for the oxidative removal of ethylbenzene

The PdPtVOx/CeO2-ZrO2 (PdPtVOx/CZO) catalysts were obtained by using different approaches, and their physical and chemical properties were determined by various techniques. Catalytic activities of these materials in the presence of H2O or SO2 were evaluated for the oxidation of ethylbenzene (EB). The PdPtVOx/CZO sample exhibited high catalytic activity, good hydrothermal stability, and reversible sulfur dioxide-poisoning performance, over which the specific reaction rate at 160°C, turnover frequency at 160°C (TOFPd or Pt), and apparent activation energy were 72.6 mmol/(gPt⋅sec) or 124.2 mmol/(gPd⋅sec), 14.2 sec-1 (TOFPt) or 13.1 sec-1 (TOFPd), and 58 kJ/mol, respectively. The large EB adsorption capacity, good reducibility, and strong acidity contributed to the good catalytic performance of PdPtVOx/CZO. Catalytic activity of PdPtVOx/CZO decreased when 50 ppm SO2 or (1.0 vol.% H2O + 50 ppm SO2) was added to the feedstock, but was gradually restored to its initial level after the SO2 was cut off. The good reversible sulfur dioxide-resistant performance of PdPtVOx/CZO was associated with the facts: (i) the introduction of SO2 leads to an increase in surface acidity; (ii) V can adsorb and activate SO2, thus accelerating formation of the SOx2- (x = 3 or 4) species at the V and CZO sites, weakening the adsorption of sulfur species at the PdPt active sites, and hence protecting the PdPt active sites to be not poisoned by SO2. EB oxidation over PdPtVOx/CZO might take place via the route of EB → styrene → phenyl methyl ketone → benzaldehyde → benzoic acid → maleic anhydride → CO2 and H2O.

Strong metal support interaction (SMSI) and MoO3 synergistic effect of Pt-based catalysts on the promotion of CO activity and sulfur resistance

In industrial applications, Pt-based catalysts for CO oxidation have the dual challenges of CO self-poisoning and SO2 toxicity. This study used synthetic Keggin-type H3PMo12O40 (PMA) as the site of Pt, and the Pt-MoO3 produced by decomposition of PMA was anchored to TiO2 to construct the dual-interface structure of Pt-MoO3 and Pt-TiO2, abbreviated as Pt-P&M/TiO2. Pt-0.125P&M/TiO2 with a molar ratio of Pt to PMA of 8:1 showed both good CO oxidation activity and SO2 tolerance. In the CO activity test, the CO complete conversion temperature T100 of Pt-0.125P&M/TiO2 was 113 ℃ (compared with 135 ℃ for Pt/TiO2). In the SO2 resistance test, the conversion efficiency of Pt-0.125P&M/TiO2 at 170 ℃ remained at 60% after 72 h, while that of Pt/TiO2 was only 13%. H2-TPR and XPS tests revealed that lattice oxygen provided by TiO2 and hydroxyl produced by MoO3 increased the CO reaction rate on Pt. According to the DFT theoretical calculation, the electronegative MoO3 attracted the d-orbital electrons of Pt, which reduced the adsorption energy of CO and SO2 from - 4.15 eV and - 2.54 eV to - 3.56 eV and - 1.52 eV, respectively, and further weakened the influence of strong CO adsorption and SO2 poisoning on the catalyst. This work explored the relationship between catalyst structure and catalyst performance and provided a feasible technical idea for the design of high-performance CO catalysts in industrial applications.

Combined removal of SO3 and HCl by modified Ca(OH)2 from coal-fired flue gas

As treatments for mainstream pollutants in coal-fired power plants have been established, the control of non-conventional pollutants, such as SO₃ and HCl, is gradually gaining attention. In this study, combined SO₃ and HCl removal is proposed based on SO₃ removal by absorber injection. However, it is challenging to selectively absorb SO₃ and HCl from SO₂-rich atmospheres. Therefore, Ca(OH)₂ was modified via ball milling and doping with CuO for the combined removal of SO₃ and HCl. The results showed that ball milling reduced the particle and grain sizes of Ca(OH)₂, which increased the active sites of Ca(OH)₂ and prolonged reaction time. After modification by ball milling, SO₃ absorption per mg of Ca(OH)₂ increased by 40 %. However, HCl removal efficiency was difficult to improve by modifying Ca(OH)₂ using only ball milling under SO₃ and SO₂ atmospheres. Therefore, the dechlorination capacity of Ca(OH)₂ was improved by adding ions during the ball milling process. Doping of Ca(OH)₂ with Cu²⁺ changed its crystal structure, weakened the diffusion resistance of HCl, and improved Ca(OH)₂ utilization. Additionally, it increased the energy of Ca(OH)₂ to adsorb HCl.

Soot Oxidation in a Plasma-Catalytic Reactor: A Case Study of Zeolite-Supported Vanadium Catalysts

The plasma-catalytic oxidation of soot was studied over zeolite-supported vanadium catalysts, while four types of zeolites (MCM-41, mordenite, USY and 5A) were used as catalyst supports. The soot oxidation rate followed the order of V/MCM-41 > V/mordenite > V/USY > V/5A, while 100% soot oxidation was achieved at 54th min of reaction over V/MCM-41 and V/mordenite. The CO2 selectivity of the process follows the opposite order of oxidation rate over the V/M catalyst. A wide range of catalyst characterizations including N2 adsorption–desorption, XRD, XPS, H2-TPR and O2-TPD were performed to obtain insights regarding the reaction mechanisms of soot oxidation in plasma-catalytic systems. The redox properties were recognized to be crucial for the soot oxidation process. The effects of discharge power, gas flow rate and reaction temperature on soot oxidation were also investigated. The results showed that higher discharge power, higher gas flow rate and lower reaction temperature were beneficial for soot oxidation rate. However, these factors would impose a negative effect on CO2 selectivity. The proposed “plasma-catalysis” method possessed the unique advantages of quick response, mild operation conditions and system compactness. The method could be potentially applied for the regeneration of diesel particulate filters (DPF) at low temperatures and contribute to the the emission control of diesel engines.

Theoretical Study of the Catalytic Activity and Anti-SO2 Poisoning of a MoO3/V2O5 Selective Catalytic Reduction Catalyst

In this paper, density functional theory has been applied to study the mechanism of anti-SO₂ poisoning and selective catalytic reduction (SCR) reaction on a MoO₃/V₂O₅ surface. According to the calculation results, the SO₂ molecule can be converted into SO₃ on V₂O₅(010) and further transformed into NH₄HSO₄, which poisons V₂O₅. If V₂O₅ and MoO₃ are combined with each other, charge separation of V₂O₅ and MoO₃, which are negatively and positively charged, respectively, occurs at the interface. In ammonium bisulfate liquid droplets on the MoO₃/V₂O₅ surface, NH₄ ⁺ tends to adhere to the V₂O₅(010) surface and can be removed through the SCR reaction and HSO₄ ^- tends to adhere to the MoO₃(100) surface and can be resolved into SO₃ and H₂O, which can be released into the gas phase. Thus, MoO₃/V₂O₅ materials are resistant to SO₂ poisoning. In the MoO₃/V₂O₅ material, Brønsted acid sites are easily formed on the negatively charged V₂O₅(010) surface; this reduces the energy barrier of the NH₃ dissociation step in the NH₃-SCR process and further improves the catalytic activity.

Modification of V2O5-WO3/TiO2 Catalyst by Loading of MnOx for Enhanced Low-Temperature NH3-SCR Performance

V₂O₅-WO₃/TiO₂ as a commercial selective catalytic reduction (SCR) catalyst usually used at middle-high temperatures was modified by loading of MnO_x for the purpose of enhancing its performance at lower temperatures. Manganese oxides were loaded onto V-W/Ti monolith by the methods of impregnation (I), precipitation (P), and in-situ growth (S), respectively. SCR activity of each modified catalyst was investigated at temperatures in the range of 100–340 °C. Catalysts were characterized by specific surface area and pore size determination (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), etc. Results show that the loading of MnO_x remarkably enhanced the SCR activity at a temperature lower than 280 °C. The catalyst prepared by the in-situ growth method was found to be most active for SCR.

Effect of SiO2 addition on NH4HSO4 decomposition and SO2 poisoning over V2O5-MoO3/TiO2-CeO2 catalyst

The deposition of NH₄HSO₄ and the poisoning effect of SO₂ on SCR catalyst are the main obstacles that restrict the industrial application of CeO₂-doped SCR catalysts. In this work, deposited NH₄HSO₄ decomposition behavior and SO₂ poisoning over V₂O₅-MoO₃/TiO₂ catalysts modified with CeO₂ and SiO₂ were investigated. By the means of characterization analysis, it was found that the addition of SiO₂ into VMo/Ti-Ce had an impact on the interaction existed between catalyst surface atoms and NH₄HSO₄. Temperature-programmed methods and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments indicated that the doping of SiO₂ promoted the decomposition of deposited NH₄HSO₄ on VMo/Ti-Ce catalyst surface by reducing the thermal stability of NH₄HSO₄ and enhancing the NH₄HSO₄ reactivity with NO in low temperature. And this improvement may be the reason for the better catalytic activity than VMo/Ti-Ce in the case of NH₄HSO₄ deposition. Accompanied with cerium sulfate species generated over catalyst surface, the conversion of SO₂ to SO₃ was inhibited in SiCe mixed catalyst. The addition of SiO₂ could promote the decomposition of cerium sulfate, which may be a potential strategy to enhance the resistance of SO₂ poisoning over CeO₂-modifed catalysts.

Field test of SO3 removal in ultra-low emission coal-fired power plants

Under the extensive implementation of ultra-low emission (ULE) facilities in coal-fired power plants of China, sulfur trioxide (SO₃) has received increasing attention due to its impact on human health and operation safety of power plants. However, systematic research and evaluation for controlling SO₃ emission in various ULE facilities are still lacking. Here, a systematic study was conducted based on 378 in situ performance evaluation tests carried out in 148 coal-fired power plants. The results illustrate that the SO₂/SO₃ conversion rate of the selective catalytic reduction devices can be controlled within 1% before and after ULE retrofit. Also, the synergistic removal efficiency of SO₃ in the low-low-temperature electrostatic precipitator and the wet electrostatic precipitator can be higher than 70%. The removal efficiency of SO₃ in the wet limestone-gypsum flue gas desulfurization scrubber is 33-64% before ULE and 31-81% after, and the average efficiency of the double scrubbers is 8.7% higher than that of the single scrubber. Due to the different SO₃ removing abilities of various technologies, the overall efficiency of SO₃ removal is in the range between 27 and 95% adopting different ULE technical routes. Average concentration of SO₃ emission can be decreased by 51.8% after ULE application.

Understanding the oxidative dehydrogenation of ethyl lactate to ethyl pyruvate over vanadia/titania

We studied the vapour-phase oxidative dehydrogenation of ethyl lactate to ethyl pyruvate over V₂O₅/TiO₂ catalysts in a fixed-bed reactor.

Supported two- and three-dimensional vanadium oxide species on the surface of β-SiC

Dispersing two-dimensional VO_x species on β-SiC offers a new approach to scale up propane ODH.

Vapor-phase dehydrogenation of ethylbenzene to styrene over a V2O5/TiO2–Al2O3 catalyst with CO2

A stable V₂O₅/TiO₂–Al₂O₃ catalyst was synthesized for the oxidative dehydrogenation of ethylbenzene to styrene using CO₂ as a mild oxidant.

Exploring the role of V2O5 in the reactivity of NH4HSO4 with NO on V2O5/TiO2 SCR catalysts

NH₄⁺ in NH₄HSO₄ is consumed during the reaction with NO, while S-species are stabilized as tridentate SO₄²⁻ on the catalysts.