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A series of alumina-pillared layered tetratitanates with different interlayer spacings (doe, = 1 5.2-1 7.0 A) has been first prepared through a step-wise exchange process and by finely changing the exchange reaction conditions such as reaction time and molar ratio of reactants in the reaction mixture, and hydrolysis conditions such as the pH and aging time used to generate the pillaring agent. Apart from the interlayer spacing, the pore diameter and specific surface area of the pillared samples can also be changed by varying the preparation conditions. The resulting aiumina-pillared layered tetratitanates were porous, with both micro-and meso-pores (average pore diameter = 61 595.8 A). The specific surface area (BET, N, , 77 K) of the starting material K,Ti ,OB (5 m2 g-') was increased by pillaring up to 56.6-105.6 m2 g-'. The relatively high surface area is mainly due to the microporous structure of the interlayered spaces formed by stable alumina pillars. The structure of the alumina-pillared layered tetratitanates was thermostable above 500 "C. The results are compared with those previously reported.The synthesis of pillared clays has led to the development of new materials with suitable pore sizes and sufficient stabilities to be used as shape-selective catalysts and molecular sieves.'*2 Pillared clays are smectite clay minerals that have been modified through the introduction of large polyoxocations into their interlayer regions. The intercalated cations are capable of preventing the collapse of the interlayer space. When they are heated, inorganic oxide clusters are formed which prop open the clay layers permanently, generating a microporous structure and a high specific surface area.There are numerous layered metal oxides which have the potential to undergo ion-exchange reactions analogous to those observed with but the non-swelling nature of most ionic layered oxides generally prevents the facile ion exchange of large inorganic 0x0 cations, although the direct reaction of a layered sodium trititanate with [A1,30,(OH),4(H,0),,]7+ (abbreviated hereafter as A1137+ ) has recently been r e p~r t e d . '~ However, amines are readily intercalated and increase the interlayer distance of the metal oxides to almost any requiredThe opened layers then facilitate the replacement of RNH3+ ions with large inorganic cations such as A1137+ Keggin ions to form thermostable porous materials pillared by inorganic oxides. This stepwise ion-exchange technique has recently been applied to the preparation of thermostable alumina-and chromia-pillared layered metal phosphates and tetratitanates.I7-,, Since the main application of the pillared materials is as shapeselective catalysts and molecular sieves, the preparation of pillared materials with a range of interlayer spacings would be advantageous in order to meet the steric requirements of different guest molecules with different kinetic diameters. However, so far there has been no report on the preparation of inorganic oxide-pillared layered metal oxides with different interlay...

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The first silica-pillared titanoniobate has been prepared by firstly intercalating layered titanoniobate with NH2(CH2)3Si(OEt)3 and subsequently thermally removing the interlayered organics, the resulting pillared material is porous and has a high thermal stability beyond 750 "C.