الفهرس 
Introduction and Object of InvestigationOnly 14 pages are availabe for public view
 |  | from | 181 |  |  |
| | | from | 181 | | |
Abstract
Preparation of supported catalysts has been considered the most common method for the high surface area exhibited by the active phase. Normally for such preparation some parameters have to be put into consideration vis, the nature of the support, the loading level of the active phase and the calcinations temperature of the prepared materials. A question has to be raised about the role of the nature of the precursor on the characterization and the surface texture properties of the final catalysts.
Copper oxide is an important catalyst in the field of heterogeneous catalysis. Copper oxides are catalysts for a variety of important reactions such as in the reduction of NOx¬ in automobile exhaust systems, oxidation – reduction
reactions, ester hydrogenolysis, promoting methanol steam reforming synthesis of methanol from CO and H2 and in water gas shift reaction.
Silica is used as a support for its high surface area, thermal stability and its inert nature. The well-dispersed forms of active supported phases can be obtained on the surface of silica.
A series of silica supported copper oxide were prepared using copper nitrate trihydrate, (CuNTH), basic copper carbonate, (BCuC), and Copper acetate monohydrate, (CuAMH), as different precursors for the oxide at different loading levels (0.5, 3 and 10) by impregnation method. The study aimed at investigating the effect of varying the copper oxide precursor on the textural characterization of these catalysts. It is worthmentioning that silica has been treated exactly as the supported catalysts for comparison reasons.
To accomplish such aim a number of techniques have been used to study the structure and the texture of the prepared catalysts vis. thermal analysis (TG & DTA), X – ray diffractometry (XRD), UV–Vis Diffuse reflectance Spectroscopy (DRS), KBr–Infrared Spectroscopy (IRS) and nitrogen adsorption measurements.
The following conclusions could be summarized from the present study:
1. Thermal analysis reveals that all the precursors supported and unsupported gave CuO at 500 oC.
2. Supporting on silica caused an enhancement in the decomposition step of the precursors.
3. X – ray diffraction confirmed the formation of the three dimensional CuO at the high loading level of supporting.
4. At the low loading level dispersion of CuO was detected on the surface of silica which was marked for the 3wt.% from the acetate precursor.
5. The diffuse reflectance spectroscopy exhibited the bands O-2 Cu+2 and O- Cu+2 due to the octahedral Cu+2 ions and also Cu – O – Cu with no reference for the formation of Cu+1.
6. The infrared spectroscopic analysis revealed the presence of physically adsorbed water and bands corresponding to CuO while those of nitrate gave a tiny feature of a trapped NO3- species and those of acetate gave weak peaks due to the carbonate group, which may be adsorbed during the decomposition process.
7. The textural study revealed some conclusions:
a. The treated silica accommodates SBET value ≈ 131 m2 gm-1, with microporous nature.
b. The unsupported CuO catalysts from the three precursors have a very low SBET values (≈ 5 m2 gm-1 from nitrate and acetate which is unreliable value while in case of carbonate precursor amounts to 18 m2 gm-1).
c. The low loading levels (0.5%) from all the series have surface areas close to that of the silica support.
d. Increasing the loading level of CuO resulted in an increase in SBET.
e. In all the supported samples mesoporous nature has been appeared which vary in portion from sample to another.
f. At the same loading level the supported CuO from carbonate precursor showed a lower SBET value, while at the high loading level the acetate supported one gave the highest SBET value. This was attributed to the variation in the amount and the nature of the evolved gases from the decomposition of the precursor.
These properties of the surface texture of the supported catalysts have been found to depend on the precursor in addition to the other known parameters.