Effect of vanadia loading on the acidic, redox and catalytic properties of V2O5–TiO2 and V2O5–TiO2/SO42− catalysts for partial oxidation of methanol

Effects of Chlorine Addition on Nitrogen Oxide Reduction and Mercury Oxidation over Selective Catalytic Reduction Catalysts

The effect of chlorine on mercury oxidation and nitrogen oxides (NO _x ) reduction over selective catalytic reduction (SCR) catalysts was investigated in this study. Commercial SCR catalysts achieved a high Hg⁰ oxidation efficiency when Cl₂ was sprayed into the flue gas. Results indicated that an appropriate concentration of Cl₂ was found to promote NO _x reduction and Hg⁰ oxidation significantly. An optimal concentration of Cl₂ (25 ppm) was found to significantly promote NO _x reduction and Hg⁰ oxidation. Moreover, we studied the effects of Cl₂ on NO _x reduction and Hg⁰ oxidation over SCR catalysts under different concentrations of SO₂. The SO₂ poisoning effect was decreased by Cl₂ when the SO₂ concentration was low (below 1500 ppm). However, sulfate gradually covered the catalyst surface over time during the reaction, which limited the impact of Cl₂. Finally, different sulfur-poisoned catalysts were examined in the presence of Cl₂. The NO _x reduction and Hg⁰ oxidation performances of sulfate-poisoned catalysts improved when Cl₂ was added to the flue gas. Mechanisms for NO _x reduction and Hg⁰ oxidation over fresh catalysts and sulfate-poisoned catalysts in the presence of Cl₂ were proposed in this study. The mechanism of Cl₂-influenced NO _x reduction was similar to that for the NH₃-SCR process. With Cl₂ in the flue gas, the number of Brønsted active sites increased, which improved catalytic activity. Furthermore, Cl₂ reoxidized V⁴⁺-OH to V⁵⁺=O and caused the NH₃-SCR process to operate continuously. The Langmuir-Hinshelwood mechanism was followed for Hg⁰ oxidation by SCR catalysts when Cl₂ was in the flue gas. Cl₂ increased the number of Lewis active sites, and catalytic activity increased. Hg⁰ adsorbed on the surface of the catalysts and was then oxidized to HgCl₂. Adding Cl₂ to the flue gas increased the strength and number of acid sites on sulfate-poisoned catalysts.

On the Activity and Selectivity of CoAl and CoAlCe Mixed Oxides in Formaldehyde Production from Pulp Mill Emissions

Contaminated methanol has very good potential for being utilized in formaldehyde production instead of its destructive abatement. The activities, selectivities and stabilities of cobalt–alumina and cobalt–alumina–ceria catalysts prepared by the hydrotalcite-method were investigated in formaldehyde production from emissions of methanol and methanethiol. Catalysts were thoroughly characterized and the relationships between the characterization results and the catalytic performances were drawn. The preparation method used led to the formation of spinel-type structures in the form of Co2AlO4 based on x-ray diffraction (XRD) and Raman spectroscopy. Ceria seems to be present as CeO2, even though interaction with alumina is possible in the fresh catalyst. The same structure is maintained after pelletizing the cobalt–alumina–ceria catalyst. The cobalt–alumina–ceria catalyst was slightly better in formaldehyde production, probably due to lower redox temperatures and higher amounts of acidity and basicity. Methanol conversion is negatively affected by the presence of methanethiol; however, formaldehyde yields are improved. The stability of the pelletized catalyst was promising based on a 16 h experiment. During the experiment, cobalt was oxidized (Co2+ → Co3+), cerium was reduced (Ce4+ → Ce3+) and sulfates were formed, especially on the outer surface of the pellet. These changes affected the low temperature performance of the catalyst; however, the formaldehyde yield was unchanged.

V2O5/TiO2 and V2O5/TiO2–SO42− catalysts for the total oxidation of chlorobenzene: one-step sol–gel preparation vs. two-step impregnation

This paper examines the effect of the preparation method of sulfated and unsulfated V₂O₅/TiO₂ catalysts on chlorobenzene total oxidation.

NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures

Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction (SCR) of NO. The results showed that the addition of Nb₂O₅ could improve the SCR activity at low temperatures and the 6wt.% additive was an appropriate dosage. The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures. The resistances to SO₂ of 3V6Nb/WTi catalyst at different temperatures were investigated. FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures, which still exhibited the reactivity with NO above 200°C on the catalyst surface. There was a synergistic effect among NH₃, H₂O and SO₂ that NH₃ and H₂O both accelerated the catalyst deactivation in the presence of SO₂ at 175°C. The thermal treatment at 400°C could regenerate the deactivated catalyst and get SCR activity recovered. The particle and monolith catalysts both kept stable NO_x conversion at 225°C with high concentration of H₂O and SO₂ during the long time tests.

Effect of MoO3 on vanadium based catalysts for the selective catalytic reduction of NOx with NH3 at low temperature

The selective catalytic reduction (SCR) activities of the MoO₃ doped V/WTi catalysts prepared by the incipient wetness impregnation method at low temperature were investigated. The results showed that the addition of MoO₃ could enhance the NO_x conversion at low temperature and the best SCR activity was obtained when the dosage of MoO₃ reached 5wt.%. The NH₃-TPD and DRIFTS experiments indicated that the addition of MoO₃ changed the type and number of acid sites on the surface of catalysts and reaction activities of acid sites were altered at the same time. The redox capacity and amount of active oxygen species got improved for V3Mo5/WTi catalyst, which could be confirmed by the H₂-TPR and transient response experiments. Water vapor inhibited the NO_x conversion at low temperature. Deposition of ammonium sulfate or bisulfate might be main reason for the loss of catalytic activity in the presence of SO₂ at low temperature. Choosing the suitable NH₃/NO ratio and elevation of reaction temperature both could weaken the influence of SO₂ on the SCR activity of the V3Mo5/WTi catalyst. Thermal treatment of the deactivated catalyst at 350°C could get the low temperature activity recovered. The decrease of GHSV improved the deNO_x efficiency at low temperature and we speculated that the rational technological process and operation parameters could contribute to the application of this kind of catalysts in real industrial environment.

High-Visible-Light Photoactivity of Plasma-Promoted Vanadium Clusters on Nanozeolites for Partial Photooxidation of Methanol

Cold VCl₃-plasma is employed for the preparation of highly dispersed vanadium oxide clusters on nanosized zeolite. Different types of zeolites, such as EMT, FAU (z.X), and Beta, are used. The activity of the prepared catalysts is studied in the selective photooxidation of methanol under polychromatic visible and UV irradiations. The physicochemical properties and catalytic performance of plasma-treated zeolite Beta (P-V₂O₅@Beta) catalyst is compared with zeolite Beta (V₂O₅@Beta) and amorphous silica (V₂O₅@SiO₂) impregnated vanadium oxide catalysts. Pure V₂O₅ is used as a reference material. The set of catalytic data shows that plasma-prepared zeolite Beta based catalyst displays the highest activity. Complementary characterization techniques including XRD, N₂-sorption, FTIR, ionic exchange, pyridine adsorption, Raman, NMR, TPR, and EDX-TEM are used to study the impact of the preparation approach on the physicochemical properties and catalytic performance of photocatalysts.

One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts

Dimethoxymethane or DMM is a versatile chemical with applications in many industries such as paints, perfume, pharmacy, and fuel additives.