Titania-Alumina Composites
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ABSTRACT Titania-alumina composites were carried out by various methods. The composite prepared by mixed gelation method showed the merits of both y-Al203 and TiO2 (anatase), and it behaved much better than the y-A1203 alone as the carrier of HDS catalyst or H2S adsorbent. Another representative composite was prepared by sol-gel method. The hydroxide of aluminium alkoxide was peptised directly with TiCI4 to form TiO2-AI203 composite sol, and then the composite membrane without support was obtained. The sizes of primary particles were around 5nm as characterised by TEM.
Introduction
As a carrier of catalyst, TiQ2 has some attractive properties. Its surface is
more homogenous in energy than that of y-alumina[1 ]. It shows resistance to SOx poisoning. It is a semiconductor, which makes charge transfer easy between Ti atoms and reactive atoms or molecules. However, its thermal stability and mechanical strength are not as good as y-alumina, and its specific surface area is relatively small. Recently, the preparation of titania-alumina composite which has the merits of both has been extensively studied[2,3,4]. We suppose that the better constituent form of the composite is that y-alumina particle plays a role of framework, which keeps good thermal stability, mechanical strength and appropriate pore structure, and titania sticks firmly on the surface of y-alumina particle, which keeps the properties of pure titania. A preparation procedure, mixed gelation method, was designed to get such a composite and the satisfying result was obtained. MoO3/AI203, MoO3-CoO/AI203 and MoO3/TiO2-AI203, MoO3-CoO/TiO2-AI203 were used to probe the adsorptive and catalytic properties of the surface of the composite. XRD, LRS and XPS were used to characterise the texture of the composite. For further study, the TiO2-AI203 composite membrane prepared by sol-gel method was investigated.
445 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Experimental Sample Preparation: Fig. 1 shows the schematic representation of the preparation of TiO2A1203 composites by mixed gelation and Fig. 2 shows the schematic representation of the preparation of Ti02-AI203 composite membrane by solgel method. AIC13 aqueous solution
4_Stirring,
N-NH3, NH4 HCO3 mixed solutionj aluminium
precipitation of
oxy-hydroxide at about 80 'C, pH 8.5-9.0
TiCI4 in iso-propyl alcohol
Aging for 0.5-1.0 h Vigorous stirring titanium oxy-hydroxide ý-precipitate onto the surface of aluminium oxy-hydroxide particles at 80 'C, pH 8.5-9.0 Aging for 0.5-1.0 h Filtration Washing with 0.3M NH 4 HCO 3 and filtration for 5-6 times to remove ClExtrude 120 'C 12 h and 550 'C 5 h TiO 2 -A1203 composite] Fig. 1 Schematic of the preparation of TiO 2 -AI 2 0 3 composites by mixed gelation
Aluminium isopropoxidej
[ Hot water ( >80'C)
=Hydrolysis and polycondensation]_ at 80-90'C , 20 mrin Addition of TiCI4 iso -propyl alcohol solution Peptisation at 80'C for 16 h to get] stable TiO 2-AI 2 0 3 composite sol Drying under the atmosphere of saturated vapour of MgCI2'6H20
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