Vietnam Journal of Catalysis and Adsorption

Volume 7, Issue 3, Oct 2018

cover 

Volume 7, Issue 3, October 2018

ISSN: 0866-7411

 

In this issue (20 articles)

open access

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REVIEW PAPER

open access logo 200x200Development of low-temperature catalysts for the selective catalytic reduction of NOx with NH3: Review

Thanh Huyen Vuong1,2,This email address is being protected from spambots. You need JavaScript enabled to view it., Anh Tuan Doan2, Thanh Huyen Pham2, Angelika Brückner1

1 Leibniz Institute for Catalysis at the University of Rostock, Albert-Einstein-Str. 29a, D-18059 Rostock, Germany
2 School of Chemical Engineering, Hanoi University of Science and Technology, 1 Dai Co Viet, Hanoi, Vietnam

ABSTRACT

Selective catalytic reduction (SCR) of nitrogen oxides by ammonia over V2O5-WO3/TiO2 catalysts is one of the most popular techniques to control NOx emission from combustion processes which, however, operates only in a rather high and narrow temperature range of 300-500°C. The temperature of other NOx sources such as diesel or lean-burn gasoline engines is much lower. Therefore, development and optimization of catalysts being highly active and selective for NH3-SCR of NOx already at temperatures well below 300°C is highly desirable. In recent years, significant efforts have been dedicated to developing de-NOx catalysts for both stationary sources and diesel engines working at low temperatures. Among various SCR catalysts, Mn-based catalysts obtained the highest low-temperature activity. However, their low SO2 and H2O resistance, and preference for N2O formation limited these catalysts for industrial applications. V2O5 supported on different materials still have attracted much attention due to high SCR activity and SO2 tolerance at low temperatures. Recently, Cu-containing small pore zeolites with a CHA or AEI structure, such as Cu-SSZ-13, Cu-SAPO-34, and Cu-SSZ-39, Cu-SAPO-18, respectively, exhibited high low-temperature activity and high-temperature excellent hydrothermal stability, and thus received much attention for applications on diesel vehicles. In this review, we will focus on the development of different catalysts for low-temperature NH3-SCR of NOx.

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RESEARCH PAPER

open access logo 200x200Potassium Coordination in K-KFI Zeolite Investigated by Synchrotron X-ray Diffraction

Son T. Le, Binh T. Nguyen, Trong D. Phammail

Faculty of Chemistry, VNU University of Science, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam

ABSTRACT

The KFI (Si/Al=4) zeolite was prepared by a hydrothermal method using 18-crown-6 as the organic structure directing agent. The synthesized material was characterized by in-house X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and N2 adsorption isotherm. The material possessed a high crystalline structure with well-defined cubic shape, large surface area, and high micropore volume. The atomic positions of atoms, potassium locations and occupancies parameters were determined from the refined Synchrotron X-ray diffraction pattern of potassium exchanged KFI. The Rietveld refinement results indicated that K+ cations were located at three different sites (SI’, SII, and SIII), at which site SII at the puckered 8-membered ring of the pau-cages is the most stable site. The elucidation of extra-framework cation sites in zeolites is crucial in understanding the structure-property relationship for zeolite catalysts and adsorbents.

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RESEARCH PAPER

open access logo 200x200Influence of Water on the Activation of Methanol over Platinum: A DFT Study

Trinh Quang Thang1,2,This email address is being protected from spambots. You need JavaScript enabled to view it., Dao Quoc Tuy1, Huynh Dang Chinh1, Pham Thanh Huyen1,This email address is being protected from spambots. You need JavaScript enabled to view it.

1 School of Chemical Engineering, Hanoi University of Science and Technology, 1 Dai Co Viet St., Hanoi, Vietnam.
2 Cambridge Centre for Advanced Research and Education in Singapore (CARES), Campus for Research Excellence and Technological Enterprise (CREATE), 1 Create Way, 138602 Singapore.

ABSTRACT

Water plays an active role in aqueous phase catalytic reactions. In this study, the effect of water on the chemical activity and selectivity of the C-H and O-H bond activation in methanol on Pt was studied using density functional theory. On clean terraces in gas phase, C-H and O-H activations are competitive with energy barriers of 88 and 82 kJ/mol, respectively. The selectivity however reverses in the presence of a monolayer of water and the O-H activation barrier is increased to 128 kJ/mol. The C-H activation barrier of 108 kJ/mol is less affected and the CH activation becomes the dominant channel, in agreement with experiments at low potentials. At higher potentials, the presence of surface hydroxyl groups opens a new hydrogen abstraction pathway with a very low barrier for O-H bond activation of 9 kJ/mol. Hydroxyl groups can also activate C-H bonds and hydrogen abstraction in methoxy has a barrier of 67 kJ/mol, but is however higher than the barrier for direct C-H activation of 36 kJ/mol.

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