الفهرس 
Chapter 1 : Introduction and Object Object of InvestigationOnly 14 pages are availabe for public view
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Abstract
1. The study of the thermal behaviour of alumina gel revealed that this material approaches the formula Ah03.2.5H2D. Phosphated alumina gel (P AlH) exhibits higher weight loss than PAlO; both revealed the probable transformation of (N&)2HP04 to NHJ12P04 due to the expulsion of NH3. Sulfated aluminas exhibited a similar thermal behaviour except for the presence of an additional weight loss step at ;:::: 850°C which supports the presence of covelently bound sulfate species to alumina surfaces.
2. The addition of (N&)2HP04 or (N&)2S04 to the aluminas does not change the crystal structure of y-Al203. Probably, the load, in both phosphated and sulfated aluminas, remains beyond that necessary for bulk aluminium phosphate or sulfate formation. However, a slightly higher degree of crystallization is noticed for phosphated (PAID) and sulfated (SAID) than those prepared from alumina gel (P AlH and SAlH).
3. Diffuse reflectance spectroscopic results show that the addition of phosphate or sulfate onto alumina gel, PAIR and SAlH, causes a blue shift in the wavelength indicating the presence of small particle sizes in these catalysts, and this was not detected in case ofP AlO and SAlO. These results support XRD results.
4. Inspecting the values of surface areas, SSET, indicates that phosphation and sulfation of the pure crystalline oxide (pAlO and SAlO) lead to DROP of surface area, whereas the phosphation and sulfation of the alumina gel (P AlH and SAlH) lead to obtaining acidified aluminas with much higher surface area. This implies that, for the samples (P AlH and SAlH), the external area is greater than in the case ofP AlO and SAlO, due to smaller particles as revealed by XR.D and DRS findings.
5.(N&)2HP04 (pH> 7) and ~)2S04(pH < 7) from solutions corresponding to 6 % load are mostly adsorbed in a different manner on the gel than on the pure oxide. After calcination, different effects on particle morphology and pore structure are observed, leading eventually to higher SSET values for P AlH and SAlH.
6. y-Al203 surfaces expose at least two different types of Lewis acid sites of different acidities, as well as different basic sites, in addition to surface-OH groups of different structures and acid-base properties. Bronsted acid sites were not detectable on y-Al203 surface.
7. The addition of phosphate ions may have resulted in:
• Decrease of various OH species, meaning that the alumina surface was modified through a sort of surface acid-base neutralization reaction with formation ofP-O surface bond .
• Formation ofP-OH groutlS.
( 117)
• Both PAlO and PAlH have at least three different types of Lewis acid sites, involving both octahedral and tetrahedral sites.
• Bronsted acid sites were detected only on the P AlH surface, while these sites were not detected on PAlO surface.
8. The addition of sulfate ions onto y-Al203 surfaces lead to the formation of two different surface species of sulfate, triply bridging sulfate and bridging bidentate sulfate. Both SAlO and SAlH have Bronsted acid sites, but in different intensities, whereas Bronsted acid sites of SAlH are much stronger than those observed on the surface of SAlO. Also, both SAlO and SAlH were found to expose Lewis acid sites.