Aerogels catalysts

Photocatalytic oxidation tests were performed in a photoreactor [2]. The flat, rectangular stainless steel reactor has dimensions of 578 mm x 113 mm and inlet/outlet ports at the two ends. The aerogel catalyst placed in a recess located at the center of the reactor was uniformly irradiated by... 

Piao, L. et al., Methane decomposition to carbon nanotubes and hydrogen on an alumina supported nickel aerogel catalyst, Catal. Today, 74,145, 2002. 

Fig. 16. Change of the absorbance signal as a function of time for (a) cyclohexene and (b) TBHP on an uncoated ZnSe IRE (thin line) and on a ZnSe IRE coated with a methyl-modified Ti-Si aerogel catalyst (solid line). At time t = 0, the concentration at the inlet of the ATR flow-through cell was switched from 0 to 3 mmol/L, and at t = 122 s, it was switched back again (50).

A series of Chromia-Alumina aerogel catalysts containing different contents of chromium was prepared by autoclave method. The specific areas of the catalysis were measured with Ng at 77°K according to the BET method. Their structural properties were determined from the X ray diffraction patterns recorded on a philips diffractometer PW 1050/70. EPR measurements were performed with a 8ruker ZOO TT spectrometer at 77°K operating in X band. DPPH was used as the g value standard. Kinetic data were obtained in dynamic pyrex microreactor operating at atmospheric pressure as described elsewhere (ref. 3). 

H. Zarrouk, A. Ghorbel, G. M. Pajonk and S. J. Teichner, EPR Investigation of Chromia Alumina Aerogel Catalysts for the Transformation of Isobutane by NO into Methacrylonitrile, Proc. 9 th Ibero Americain Symposium on Catalysis, Lisbon, July 16-21, 1984, pp 339 - 348. 

In this present work, the objective is to develop a supercritical drying method which prepares aerogel catalysts with tunable physical and chemical properties. For this purpose, catalysts are prepared using supercritical drying and bulk densities of the catalysts are measured and compared with the ones of the xerogels. 

Schneider, M. Titania Based Aerogel Catalysts, PhD Dissertation, ETH, Zurich, 1994. 

More recently, it has been shown that a thoria "aerogel catalyst is superior to the thoria-hydrogel and thoria-on-pumice catalysts. High yields at a lower temperature (310°) and high flow rates are obtained. ... 

Mizushima, Y. Hori, M. Alumina aerogel catalysts prepared by two supercritical drying method used in methane combustion. J. Mater. Res. 1996, 31. 

A somewhat more complicated way to do this reaction is to use what is called a thorium oxide "aerogel" catalyst. A lower temperature and a higher... 

In a previous study, we found that Pd (lwt%) catalysts supported on finely divided aliunina aerogels were more active, in the oxidation of CO by NO and O2, than both Pd and Pt-Rh supported on commercial aluminas [2], More recently, a study of propane oxidation over Pd supported on alumina-based aerogel catalysts led to the conclusion that favorable ensembles of active sites contituted by Pd° atoms and Pda" " ions might exist for this reaction [3],... 

Sol-gel synthesis conditions, supercritical drying conditions, catalytic activity in bcnzylation of benzene, surface area and overall pore volumes of xerogcl and aerogel catalyst are shown in Table 3. 

Table 3. Total conversion of bcn/yl chloride in ben/ylation of benzene (Xb). surface area (Sa) and overall pore volumes (Vp) of xerogel and aerogel catalyst...

Pore size distribution plots of the xerogel and aerogel catalyst (Figure 12) indicate that disiribuiion of pore sizes is broad tor both catalyst types. RIuhIcs and Brown 1129.130) have... 

Figure 13. FTIR spectra of the xcrogcl and aerogel catalyst.

Since alumina/silica structure of both catalyst types is very similar, higher catalytic activity of the aerogel catalyst is explained by larger surface area, overall pore volume and larger fraction of 4.8-6.1 nm radius pores. 

Activation temperature of the aerogel catalyst influences catalytic activity, as shown in Table 4. 

Table 4. t he influence of aerogel catalyst activation temperature (catalyst samples were activated in air for 2 hours) on the total conversion ofben/yl chloride (Xb)... 

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