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Ceramic microporous membranes with pore sizes < 2 nm are known for their relatively high chemical, mechanical, and thermal stability, and they offer potential applications in gas purification and separation, pervaporation, and nanofiltration processes. However, very few microporous ceramic materials with a pore size < 1 nm (therefore suitable for membrane applications) are available. Amorphous silica membranes with pore sizes of between 0.3±0.5 nm have been studied extensively over the past decade.[1] However, ceramic sol±gel membranes with a narrow pore size distribution and pore sizes in the range of 0.6±1.3 nm are scarce.[2] Although microporous silica is a very selective membrane material for hydrogen separation [3] and pervaporation of water from liquid mixtures, [4] its chemical stability in alkaline media and strong electrolyte solutions is limited. [5] The amorphous phase of titania, which is known to be microporous, is expected to be more stable under these conditions. We prepared defect-free microporous titania membranes of between 50±150 nm thickness with a maximum pore size of~0.9 nm. These membranes demonstrated ideal hydrogen/hydrocarbon permselectivities above the theoretical limit for Knudsen diffusion and have also been shown to be selective in the pervaporation of water from water/1,4-dioxane and water/glycol binary liquids. Moreover, nanofiltration experiments have showed that these membranes have a molecular weight cut-off below 400, indicating their potential for water purification applications. Attempts in the 1990s to prepare microporous titania membranes already showed some promising results, but the average pore sizes obtained in those studies were~1.5 nm, and the Knudsen diffusion limit was not exceeded.[6] More recently, microporous titania membranes attracted attention as nanofiltration membranes [7] and molecular weight cut-offs ranging between 500±600 were reported. We studied the relationship between sol±gel processing conditions and the titania microstructure. Polymeric titania sols in ethanol were prepared by mixing titanium alkoxide solutions with water and nitric acid. Unlike silica, which does not crystallize, amorphous titania easily converts into crystalline anatase during synthesis. Low molecular weight polymeric sols were obtained only when the hydrolysis conditions were strictly controlled. The rate of hydrolysis of titanium alkoxides by water is extremely high [8] and any local excess of water at any moment had to be avoided. For a given titanium concentration, the hydrolysis-condensation reactions were governed by two parameters, the initial hydrolysis ratio . The hydrolysis of titanium tetraethoxide in the presence of different amounts of acid and water led to sols, turbid or clear gels, or precipitates, depending on r w and r a , as shown in Figure 1a.The main determining parameter for the final particle size was found to be r w , which had to be kept at values below 2 in order to prevent fast gelation of the sol. A pH > 3 solution was required to form polymeric so...

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Highly loaded copper catalysts supported on alumina are synthesized applying the cyclic two-step CVD of the precursor copper(II)diethylamino-2-propoxide in a fluidized-bed reactor. Copper/zinc oxide/alumina composites are synthesized by either the CVD of the precursor bis[bis(trimethylsilyl)amido]zinc on Cu/Al 2 O 3 , or the CVD of the Cu precursor on Zn-pretreated alumina, impregnating with diethyl zinc in addition. The composites are extensively characterized by atomic absorption spectroscopy (AAS), elemental analysis (EA), mass spectrometry (MS), N 2 physisorption, N 2 O reactive frontal chromatography (RFC), and X-ray diffraction (XRD). The Cu and ZnO nanoparticles originating from the efficient two-step procedure, consisting of adsorption and subsequent decomposition of the adsorbed species in two separated steps, are highly dispersed, X-ray amorphous, and, in the case of the Cu-containing catalysts, have high specific Cu surface areas. The catalytic activities are determined both in methanol synthesis, to judge the contact between the deposited Cu and ZnO nanoparticles, and in the steam reforming of methanol (SRM) to probe the stability of the Cu particles. The turn-over frequencies (TOF) in methanol synthesis of these Cu/ZnO/Al 2 O 3 catalysts are higher than that of a commercial ternary catalyst. The varied sequence of the CVD of Cu and ZnO on alumina leads to catalysts with similar activities in the case of similar specific Cu areas.

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