High-temperature catalyst supports and ceramic membranes: Metastability and particle packing

Parameters and/or processes responsible for the stability of catalyst supports and ceramic membranes are discussed. Two major parameters/processes were identified which are responsible for the stability of sol-gel derived nanostructured oxides at elevated temperatures. They are metastable-to-stable phase transformation and structure and packing of primary particles within the aggregate. Based on these observations, strategies to develop thermostable nanostructured oxides for high-temperature membrane and catalyst applications are discussed by taking titania and titania-alumina nanocomposites as examples

Heterogeneous Nucleation of Protein Crystals on Fluorinated Layered Silicate

Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface

Characterization and catalytic activity of Ni-Al and Zn-Cr mixed oxides obtained from layered double hydroxides

In this work, the preparation of Ni-Al and Zn-Cr layered double hydroxides (LDHs) and their transformations upon calcination are described. The LDHs were prepared from their nitrate salts by pH controlled precipitation. They were characterized before and after calcination by scanning electron microscopy (SEM). X-ray diffractometry (XRD) and BET surface area measurements. The acid-base properties of the dehydrated materials were also investigated by temperature programmed CO, desorption and the double-bond isomerization reaction of I-butene. It was found that upon calcination mixed oxides with large surface areas were formed, which possessed mainly acidic sites of moderate strength

Positional isomerization of dialkylnaphthalenes: A comprehensive interpretation of the selective formation of 2,6-DIPN over HM zeolite

A new ab initio method was developed to supply reliable molecular dimensions for catalytic studies. For the DIPN isomers, calculations at correlated level revealed that the 2,6-isomer has the best molecular shape and dimensions concerning molecular transportation in the channel system of mordenite (M) zeolite. Adsorption rate measurements supported this theoretical finding According to the ab initio calculations performed at correlated level, the2,6- and 2,7-DIPN molecules may transform into each other via 1,2-isopropyl shift at an appropriate temperature in the main channel of mordenite. Isomerization reactions of 2,6-DIPN carried out over HM at high temperatures resulted in 2,7-DIPN in the reaction mixture supporting the theoretical results. Theoretical and experimental studies revealed that the selective formation of 2,6-DIPN over HM zeolite is the result of diffusion-controlled shape-selective catalysis, i.e., product selectivity is operative in this case