Highly active OMS-2 for catalytic ozone decomposition under humid conditions

Four kinds of cryptomelane-type octahedral molecular sieve(OMS)-2-X(the X represents the molar ratio of KMnO4/MnAc2) were prepared as catalytic materials for ozone decomposition through a one-step hydrothermal reaction of KMnO4 and MnAc2, by changing their molar ratios. These samples were characterized by N2 adsorption–desorption, X-ray di raction(XRD), transmission electron microscopy(TEM), scanning electron microscopy(SEM), temperature programmed reduction by H2(H2-TPR) and X-ray photoelectron spectroscopy(XPS). Among them, the OMS-2-0.7 sample showed the best O3 conversion of 92% under high relative humidity(RH) of 90% and gas hourly space velocity of 585,000 h-1. This was accordingly thought as a possible way for purifying ozone-containing waste gases under high RH atmospheres. The e ciency of ozone decomposition of the prepared OMS-2-X sample was found to be related to specific surface area, particle size, surface oxygen vacancies, and Mn3+ cation amounts. The one-step hydrothermal synthesis was shown to be a simple method to prepare the considerably active OMS-2 solids for ozone decomposition.

N/Ce doped graphene supported Pt nanoparticles for the catalytic oxidation of formaldehyde at room temperature

Pt catalysts with nitrogen-doped graphene oxide (GO) as support and CeO_(2)as promoter were prepared by impregnation method,and their catalytic oxidation of formaldehyde (HCHO) at room temperature was tested.The Pt-CeO_(2)/N-rGO (reduced GO) with a mass fraction of 0.7% Pt and 0.8%CeO_(2)exhibited an excellent catalytic performance with the 100% conversion of HCHO at room temperature.Physicochemical characterization demonstrated that nitrogendoping greatly increased the defect degree and the specific surface area of GO,enhanced the dispersion of Pt and promoted more zero-valent Pt.The synergistic effect between CeO_(2)and Pt was also beneficial to the dispersion of Pt.Nitrogen-doping promoted the production of more Ce3+ions,generating more oxygen vacancies,which was conducive to O_(2)adsorption.As a result,the catalyst exhibited enhanced redox properties,leading to the best catalytic activity.Finally,an attempt to propose the reaction mechanism of HCHO oxidation has been made.

Selective catalytic oxidation of ammonia to nitrogen over orderly mesoporous CuFe_2O_4 with high specific surface area

Orderly mesoporous CuFe2O4spinel-type mixed oxide with high specific surface area was prepared successfully by a hard-template method in which KIT-6mesoporous silica was selected as the hard template.The KIT-6 hard template and CuFe2O4samples were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,X-ray fluorescence,transmission electron microscopy,scanning electron microscopy,nitrogen physisorption,and hydrogen-temperature programmed reduction.The KIT-6 hard template had perfect crystallization and ordered mesoporous structure with a probable pore distribution of about 9.1 nm,large enough to be filled by the spinel precursor.The mesoporous CuFe2O4spinel oxide synthesized inside the KIT-6 mesopores had a relatively small pore size(4.3 nm),orderly arrangement,and high specific area(194 m2/g).The catalytic activity of the mesoporous CuFe2O4was tested for the selective oxidation of ammonia to nitrogen.The conversion of ammonia reached nearly 100%at 300°C with a nitrogen selectivity as high as 96%.The nitrogen selectivity remained high with increasing temperature and even maintained a value of80%at 600°C.

Facile synthesis of Ag-modified manganese oxide for effective catalytic ozone decomposition

O3 decomposition catalysts with excellent performance still need to be developed. In this study, Ag-modified manganese oxides(AgMnOx) were synthesized by a simple co-precipitation method. The effect of calcination temperature on the activity of MnOx and AgMnOxcatalysts was investigated. The effect of the amount of Ag addition on the activity and structure of the catalysts was further studied by activity testing and characterization by a variety of techniques. The activity of 8%AgMnOxfor ozone decomposition was significantly enhanced due to the formation of the Ag1.8 Mn8 O16 structure, indicating that this phase has excellent performance for ozone decomposition.The weight content of Ag1.8 Mn8 O16 in the 8%AgMnOxcatalyst was only about 33.76%, which further indicates the excellent performance of the Ag1.8 Mn8 O16 phase for ozone decomposition. The H2 temperature programmed reduction(H2-TPR) results indicated that the reducibility of the catalysts increased due to the formation of the Ag1.8 Mn8 O16 structure.This study provides guidance for a follow-up study on Ag-modified manganese oxide catalysts for ozone decomposition.

Detrimental role of residual surface acid ions on ozone decomposition over Ce-modified γ-MnO2under humid conditions

In the study,the catalyst precursors of Ce-modifiedγ-MnO2 were washed with deionized water until the pH value of the supernatant was 1,2,4 and 7,and the obtained catalysts were named accordingly.Under space velocity of 300,000 hr-1,the ozone conversion over the pH=7 catalyst under dry conditions and relative humidity of 65%over a period of 6 hr was 100%and 96%,respectively.However,the ozone decomposition activity of the pH=2 and 4 catalysts distinctly decreased under relative humidity of 65%compared to that under dry conditions.Detailed physical and chemical characterization demonstrated that the residual sulfate ions on the pH=2 and 4 catalysts decreased their hydrophobicity and then restrained humid ozone decomposition activity.The pH=2 and 4 catalysts had inferior resistance to high space velocity under dry conditions,because the residual sulfate ion on their surface reduced their adsorption capacity for ozone molecules and increased their apparent activation energies,which was proved by temperature programmed desorption of O2 and kinetic experiments.Long-term activity testing,X-ray photoelectron spectroscopy and density functional theory calculations revealed that there were two kinds of oxygen vacancies on the manganese dioxide catalysts,one of which more easily adsorbed oxygen species and then became deactivated.This study revealed the detrimental effect of surface acid ions on the activity of catalysts under humid and dry atmospheres,and provided guidance for the development of highly efficient catalysts for ozone decomposition.

Ce-promoted Mn/ZSM-5 catalysts for highly efficient decomposition of ozone

Manganese oxides supported by ZSM-5 zeolite(Mn/ZSM-5) as well as their further modified by Ce promoter were achieved by simple impregnation method for ozone catalytic decomposition. The yCe20Mn/ZSM-5–81 catalyst with 8% Ce loading showed the highest catalytic activity at relative humidity of 50% and a space velocity of 360 L/(g × hr), giving 93% conversion of 600 ppm O_(3) after 5 hr. Moreover, this sample still maintained highly activity and stability in humid air with 50%–70% relative humidity. Series of physicochemical characterization including X-ray diffraction, temperature-programmed technology(NH_3-TPD and H_(2)-TPR), X-ray photoelectron spectroscopy and oxygen isotopic exchange were introduced to disclose the structure-performance relationship. The results indicated that moderate Si/Al ratio(81) of zeolite support was beneficial for ozone decomposition owing to the synergies of acidity and hydrophobicity. Furthermore, compared with 20 Mn/ZSM-5-81, Ce doping could enhance the amount of low valance manganese(such as Mn^(2+) and Mn^(3+)). Besides, the Ce^(3+)/Ce^(4+) ratio of 8Ce20Mn/ZSM-5-81 sample was higher than that of 4Ce_(2)0 Mn/ZSM-5-81. Additionally, the synergy between the MnO_x and CeO_(2) could easily transfer electron via the redox cycle, thus resulting in an increased reducibility at low temperatures and high concentration of surface oxygen. This study provides important insights to the utilization of porous zeolite with high surface area to disperse active component of manganese for ozone decomposition.