الفهرس 
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Abstract
Titania was precipitated from hydrated titanium chloride by the addition of 10% NH4OH at 285K during stirring pH 9. The differential thermograms of TC catalysts show two endothermic effects at 110-120oC and 280-310oC, the first effect is ascribed to the loss of physisorbed water whereas the latter endotherm may be attributed to dehydroxylation An additional endotherm at 300oC was exceptionally exhibited by TC25. This chromia-rich catalyst exhibited also an exotherm at 390oC attributed to Cr(OH)3→Cr2O3 transition. ZC catalysts showed two endotherm around 120 and 275oC, the former is assigned for the loss of physisorbed water and the latter for dehydroxylation .Two exothermic effects were shown by ZC catalysts , the 315oC-exotherm may be ascribe to same structural changes in zirconia. The 425- 435oC exotherm may be attributed to the aggregation of chromium ion to give Cr2O3 phase .ZTC samples showed two endotherms at 105-145oC and 205-325oC. Samples ZTC0 and ZTC5 showed exotherms around 605oC . Because these exothems are exhibited by samples containing 0-5wt%, these exotherms may account for some reactions between TiO2 and ZrO2. The x-ray diffraction was investigated for 1173oC calcinations products. Both anatase and rutile are shown in the XRD patterns, the intensity of rutile peaks increased whereas those of anatase decreased with the increase of chromia content which may indicate that chromia enhances anatase→ rutile transition. The textural parameters of the investigated catalysts and their change with thermal treatment and chemical composition may be summarized as follows :(1) For TC catalysts, the surface areas as determined by the BET-, t- and α- methods are comparable referring thus to the accuracy of the measurements and the correct choice of the reference solid samples.