Comparative Calorimetric Studies of the Acidity of Zeolites by Static and Temperature-Programmed Methods of Ammonia Adsorption and Desorption

ABSTRACTThe adsorption and desorption kinetics for SiCl4 and SiCl2H2 on Si(111) 7×7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Both LITD and TPD experiments monitored SiCl2 as the main desorption product at 950 K at all coverages of SiCl4 and SiCl2H2 on Si(111) 7×7.HC1 desorption at 850 K and H2 desorption at 810 K were also observed following SiCl2H2 adsorption. Isothermal LITD measurements of SiCl4 and SiCl2H2) adsorption on Si(111) 7×7 revealed that the initial reactive sticking coefficient decreased with increasing surface temperature for both molecules. The temperature-dependent sticking coefficients were consistent with precursor-mediated adsorption kinetics. Isothermal LITD studies of SiC12 desorption revealed second-order SiCl2 desorption kinetics. The desorption kinetics were characterizedby a desorption activation energy of Ed = 67 kcal/mol and a preexponential of vd = 3.2 cm2/s. TPD studies observed that the HCI desorption yield decreased relative to H2 and SiCl2 desorption as a function of surface coverage following SiCl2H2 exposure. These results indicate that when more hydrogen desorbs as H2 at higher coverages, The remaining chlorine is forced to desorb as SiCl 2.

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Low Temperature CO Oxidation over Cobalt Catalysts Supported on Mesoporous CeO2

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.643.76 ◽

2013 ◽

Vol 643 ◽

pp. 76-82 ◽

Cited By ~ 2

Author(s):

Jun Jie Tian ◽

Wei Na ◽

Hua Wang ◽

Wen Gui Gao

Keyword(s):

Crystal Structure ◽

Co Oxidation ◽

Mesoporous Structure ◽

Cobalt Catalysts ◽

Precipitation Method ◽

Molar Ratio ◽

N2 Adsorption ◽

Adsorption And Desorption ◽

Low Temperature Co Oxidation ◽

Temperature Programmed

Mesoporous CeO2 was first synthesized by hydrothermal method, and then used to synthesize different content of (Co3O4)x/CeO2 (x was the molar ratio of Cu and Co) by deposition-precipitation method. The fresh and doped catalysts were characterized by X-ray diffraction (XRD), N2 adsorption and desorption, H2 temperature programmed reduction (H2-TPR) and O2 temperature programmed desorption (O2-TPD) to study the crystal structure, surface area, and the mechanism of CO oxidation. The results show that: In XRD pattems, the doped cobalt amounts of samples from x=20% to x=100% have Co3O4 crystal structure. The N2 adsorption and desorption indicated the samples were mesoporous structure. Compared with other samples, the better reducibility and activity oxygen species of (Co3O4)50%/CeO2 coincided with its better catalytic activity.

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Reflection Absorption Infrared Spectroscopy and Temperature-Programmed Desorption Studies of the Adsorption and Desorption of Amorphous and Crystalline Water on a Graphite Surface

The Journal of Physical Chemistry B ◽

10.1021/jp0528111 ◽

2005 ◽

Vol 109 (35) ◽

pp. 16836-16845 ◽

Cited By ~ 83

Author(s):

Amandeep S. Bolina ◽

Angela J. Wolff ◽

Wendy A. Brown

Keyword(s):

Infrared Spectroscopy ◽

Temperature Programmed Desorption ◽

Graphite Surface ◽

Adsorption And Desorption ◽

Reflection Absorption Infrared Spectroscopy ◽

Crystalline Water ◽

Temperature Programmed

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Structure, Acidity, and Redox Aspects of VOx/ZrO2/SiO2 Catalysts for the n-Butane Oxidative Dehydrogenation

Catalysts ◽

10.3390/catal10050550 ◽

2020 ◽

Vol 10 (5) ◽

pp. 550

Author(s):

José-Luis Sánchez-García ◽

Brent E. Handy ◽

Ilse N. Ávila-Hernández ◽

Angel G. Rodríguez ◽

Ricardo García-Alamilla ◽

...

Keyword(s):

Oxidative Dehydrogenation ◽

Cyclic Compound ◽

Alder Reaction ◽

Diels Alder ◽

Behavior Changes ◽

X Ray Diffraction ◽

Ammonia Adsorption ◽

Diels Alder Reaction ◽

Nh3 Adsorption ◽

Temperature Programmed

ZrOx/SiO2 and VOx/ZrOx/SiO2 catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N2 physisorption, X-ray diffraction, Raman spectroscopy, and ammonia adsorption microcalorimetry. Tetragonal ZrO2 and zircon (ZrSiO4) were present at 25 wt % Zr, but only amorphous zirconia overlayer existed for lower loadings. At lower Zr loadings (5 wt %–10 wt % Zr), exposed silica surface leads to V2O5 crystallites and isolated VO4 species, although V reducibility behavior changes, from being similar to VOx/SiO2 (5 wt % Zr) to showing VOx/ZrO2 behavior at 10 wt % Zr, and a diminished total amount of reducible V. Highly acidic ZrO2 sites are covered by the vanadium grafting, forming weaker sites (60–100 kJ/mol NH3 adsorption strength). Catalytic conversion and selectivity for the oxidative dehydrogenation of n-butane (673 K, n-C4/O2 = 2.2) over VOx/ZrOx/SiO2 show that 1,3-butadiene is favored over cis-2-butene and trans-2-butene, although there is some selectivity to the 2-butenes when VOx/ZrO2 behavior is evident. At low Zr loadings, butadiene formed during reaction acts as the diene species in a Diels–Alder reaction and gives rise to a cyclic compound that undergoes further dehydrogenation to produce benzaldehyde.

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