Showing papers by "Changbin Zhang published in 2020"

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

Abstract: Ag/γ-Al2O3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al2O3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al2O3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al2O3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al2O3. Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al2O3, but not on microsized γ-Al2O3. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts. Detailed atom-level anchoring mechanism of Ag species on γ-Al2O3 is largely unknown for the widely used Ag/γ-Al2O3 catalyst. Here, the authors demonstrate that single-Ag atom can be only anchored by the terminal hydroxyls on the (100) surfaces of γ-Al2O3 through consuming two or three terminal hydroxyls.

Identification of a Facile Pathway for Dioxymethylene Conversion to Formate Catalyzed by Surface Hydroxyl on TiO2-Based Catalyst

Abstract: Formaldehyde (HCHO) is either a reactant, intermediate, or product in numerous industrial catalytic reactions; therefore, revealing the full transformation process of HCHO during heterogeneous cata...

Novel CeMnaOx catalyst for highly efficient catalytic decomposition of ozone

Abstract: Novel CeMnaOx (a is the molar ratio of Mn to Ce) catalysts for catalytic decomposition of ozone (O3) under high GHSV conditions were successfully synthesized by a facile homogeneous precipitation method. CeMn10Ox showed ozone conversion of 96 % for 40 ppm O3 under relative humidity (RH) of 65 % and space velocity of 840 L·g−1 ·h-1 after 6 h at room temperature, which is far superior to the performance of the α-Mn2O3 (38 %). The ozone decomposition activity of α-Mn2O3 increased by a factor of 2.5 with the addition of Ce. XRD, XPS, H2-TPR, O2-TPD, EXAFS and DFT calculations data confirmed that cerium-manganese complex oxides with enhanced surface area were formed, which played a key role in the decomposition of ozone. This study provides important insights for developing improved catalysts for gaseous ozone decomposition that can be prepared by a simple method, and promoting the performance of manganese oxides for practical ozone elimination.

Detrimental role of residual surface acid ions on ozone decomposition over Ce-modified γ-MnO2 under humid conditions

Abstract: In the study, the catalyst precursors of Ce-modified γ-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.

Enhancing Oxygen Vacancies of Ce-OMS-2 via Optimized Hydrothermal Conditions to Improve Catalytic Ozone Decomposition

Abstract: In this study, a series of Ce-OMS-2 catalysts were synthesized by a hydrothermal method, their physicochemical properties and catalytic activity for ozone decomposition were evaluated. The results ...

Insights into Designing Photocatalysts for Gaseous Ammonia Oxidation under Visible Light.

Abstract: Excessive emission of ammonia (NH3) gives rise to a number of negative effects on the environment and human health. Photocatalysis is an efficient method to eliminate gaseous NH3; however, photocat...

Formaldehyde Oxidation on Pd/TiO2 Catalysts at Room Temperature: The Effects of Surface Oxygen Vacancies

Abstract: High reduction temperature generally induces the agglomeration of supported noble metals. Howerve, we found that high temperature reduction did not induce Pd particles sintering but improved Pd dispersion. Multiple methods were further carried out to illuminate the abnormal phenomenon. The results indicated more surface oxygen defects and diffusion of Pd particles were simultaneously induced by high temperature reduction. During diffusion process of Pd particles, they were trapped by the oxygen defects because of the strong metal-support interaction, which led to improvement of Pd dispersion on the Pd/TiO2-450R catalyst. In addition, more surface oxygen vacancies on the Pd/TiO2-450R catalyst resulted in more active sites of H2O activation to form abundant surface OH groups which further enhanced adsorbed O2 activation and mobility, and then opening a more effective pathway for HCHO oxidation, which result in its high activity of Pd/TiO2-450R for ambient HCHO oxidation.

Tuning the fill percentage in the hydrothermal synthesis process to increase catalyst performance for ozone decomposition.

Abstract: The performance of Ce-OMS-2 catalysts was improved by tuning the fill percentage in the hydrothermal synthesis process to increase the oxygen vacancy density. The Ce-OMS-2 samples were prepared with different fill percentages by means of a hydrothermal approach (i.e. 80%, 70%, 50% and 30%). Ce-OMS-2 with 80% fill percentage (Ce-OMS-2-80%) showed ozone conversion of 97%, and a lifetime experiment carried out for more than 20 days showed that the activity of the catalyst still remained satisfactorily high (91%). For Ce-OMS-2-80%, Mn ions in the framework as well as K ions in the tunnel sites were replaced by Ce4+, while for the others only Mn ions were replaced. O2-TPD and H2-TPR measurements proved that the Ce-OMS-2-80% catalyst possessed the greatest number of mobile surface oxygen species. XPS and XAFS showed that increasing the fill percentage can reduce the AOS of Mn and augment the amount of oxygen vacancies. The active sites, which accelerate the elimination of O3, can be enriched by increasing the oxygen vacancies. These findings indicate that increasing ozone removal can be achieved by tuning the fill percentage in the hydrothermal synthesis process.