الفهرس 
Introduction and Object of Investigation
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Abstract
This study was devoted to synthesize diethyl ether (DEE) over selective and active Phosphotungestic acid (PWA) supported on different nano γ-alumina catalysts. Their catalytic activity and selectivity towards DEE formation were correlated with the effects of both textural and structural changes through the heat treatments to achieve this object. The following methods and techniques were conducted as follow: 1- Preparation of the investigated catalysts A. Preparation of different nano alumina i- Aluminum hydroxide, as a source of γ-Al2O3(I), was prepared by precipitation method from aluminum nitrate nonahydrate Al(NO3)3.9H2O using NH4OH at pH=7. Then the precipitate was dried for 24h at 120oC in an oven before calcined at 500oC in muffle furnace in a static air atmosphere for 3h. ii- Aluminum hydroxide, as a source of γ-Al2O3(II), was prepared by precipitation method from aluminum nitrate nonahydrate Al(NO3)3.9H2O using NH4OH at pH=7 in presence of PEG as a dispersant and structure directing agent. Then the precipitate was dried for 24h at 120oC in an oven before calcined at 500oC in muffle furnace in a static air atmosphere for 3h. iii- Pure nano γ-Al2O3(III) was prepared by precipitation with urea method. Mixture of aluminum nitrate nonahydrate (Al(NO3)3.9H2O and urea was refluxed for 8h and then the resulting gel was dried at 120 oC. The dry solid mixture was heated very slowly at 250 oC for about 3h till the gas evolution due to decomposition of the nitrates is complete. The nitrate free sample was ground to a fine powder and then calcined at 500 oC in muffle furnace in a static air atmosphere for 3h. B. Preparation of supported catalysts The samples of PWA supported on γ-Al2O3 (I, II and III) were prepared by the impregnation method. Calculated amounts of PWA were dissolved in small amounts of bi-distilled water. The PWA solutions were admixed carefully with calculated amounts of aluminum oxide (I, II and III) calcined at 500oC till formation of homogeneous pastes. The mixtures were dried in an oven at 100oC for 24h. The contents of PWA were (0.5, 1, 3, 5, 10, 20, 30 and 40 wt.%). All the supported samples were calcined at 300, 400, 500 and 600oC for 3h in a static air atmosphere. 2- characterization To achieve the aim of this study, the following techniques have been used to characterize the original and calcined catalysts together with determination of the active sites responsible for the catalytic activity of these catalysts. These techniques include: a- Thermal analysis (TGA& DTA) The thermal decomposition of the parent materials was followed by TGA and DTA. It was identified that pure precursor and PWA are thermally decomposed at 500 oC, to give their corresponding oxides. No solid-solid interaction occurs between PWA and different γ-alumina to form a new compound till 600 oC as evidence from the DTA profiles. b- X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) All the prepared calcined catalysts of PWA supported on different γ-alumina were characterized by FTIR and XRD, the XRD pattern indicates that the prepared different alumina is of type γ (Gamma). The FTIR spectrum of the different loadings of PWA on different nano γ-alumina indicates that the positions of all peaks have no apparent changed. However, the intensities of peaks are decreased. c- Transmittance electron microscopy (TEM) TEM images of different γ-Al2O3 (I, II and III) show no regular shapes but forming aggregates. While, a TEM image of 20 wt.% PWA supported on nano γ-Al2O3 (I, II and III) catalysts show more dense aggregates with average particle size of about 14.5-19 nm. 3- Nitrogen gas adsorption Nitrogen adsorption-desorption isotherms for the prepared catalysts calcined at different calcination temperatures (300- 600oC) were measured at liquid nitrogen temperature (-196oC). The results revealed that, the texture characteristic of different γ-alumina changed by the addition of PWA. Moreover, the textures of all catalysts were characterized by Va-t plots and pore size distribution which are exhibit mesoporous nature. 4- Acidity of the catalysts The results of acidity determination using IPA and chemisorptions of PY and DMPY revealed that: a. The γ-Al2O3 (I, II and III) catalysts are acidic catalysts with major (L) and minor (B) acid sites, and take place the following order: γ- Al2O3 (III) > γ- Al2O3 (I) > γ- Al2O3 (II) b. The addition of 20 wt. % PWA to γ-Al2O3 (I, II and III) significantly increases the (B) as major and (L) as minor acid sites. 5- Catalytic activity • The catalytic dehydration of ethanol to DEE over pure nano γ-Al2O3 (I, II and III) supported PWA (0.5-40 wt. %) was studied. The influence of the different catalytic parameters such as reaction temperature, catalyst weight, calcination temperature and stability of the most active catalysts were studied to achieve the optimum reaction conditions. In general, all of the prepared catalysts were active and selective toward DEE formation under our experimental conditions. Moreover, the catalysts containing 20 wt. % PWA supported on γ-Al2O3 (I, II and III) calcined at 500oC are the most active and selective catalysts toward DEE formation. The yields of DEE over 20 wt.% PWA supported on γ-Al2O3 (I, II and III) catalysts were 60, 49 and 72%, respectively. • Good correlations were obtained between catalytic activities of these catalysts and their acidity (the number and strength of the acid sites). • The results indicated that, the intermediate strength of acidic sites play a crucial role in directing the reaction of ethanol to DEE and suppressing ethylene formation. • Finally, the mechanism of ethanol dehydration over these catalysts was proposed.