Hydrothermally stable acid-modified ZSM-22 zeolite for selective propylene production via steam-assisted catalytic cracking of n-hexane

To enhance the textural properties and the hydrothermal stability of porous catalysts, ZSM-22 zeolite samples were treated with different concentrations of HF aqueous solutions (0.7, 1.0 and 1.5 wt%). ZSM-22 samples that were treated with 0.7 and 1.0 wt% HF aqueous solutions showed a selective removal of aluminum atoms from TON framework. On the other hand, more concentrated HF (1.5 wt %) caused the leaching of silicon atom from the zeolites framework. The HF treated ZSM-22 samples showed smaller crystals size, better hydrothermal stability as reflected by intact textural properties as well as their mesoporosity. The modified samples also showed enhanced acidity with lower Bronsted acidity than the parent ZSM-22. ZSM-22 samples modified with low HF concentrations (0.7 and 1.0 wt%) showed better initial conversions in steam catalytic cracking (SCC) of hexane, which can be attributed to the enhancement in the acidity. However, deactivation rate was not enhanced after the HF treatment. The HF modified ZSM-22 samples showed more BTX selectivity which can be attributed to their larger external surface areas. The HF-treated samples lost more acidity, especially Bronsted acidity, after SCC reaction than the parents ZSM-22 zeolite

Substantial reduction of critical current for magnetization switching in an exchange-biased spin-valve

Great interest 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions11, 12 of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices13: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 108 to 107 A cm-2. In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 106 A cm-2. We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory