High-temperature evacuation

Chemisorption measurements of either CO or hydrogen on transition metals mounted on zeolite substrates require considerable care for adequate interpretation. The zeolite lattices after high-temperature evacuation can adsorb large amounts of hydrogen, and divalent cations such as calcium can adsorb large amounts of CO. 

Similar results were found for nitrogen adsorbed in HZSM-5 and HY zeolites[30]. A 2352 cm l band was observed only under conditions (high temperature evacuation) where Lewis acid sites could be anticipated. The frequency of the N2 interacting with Bronsted acid sites... 

The simplest version of this hypothesis (84) is that inherently active sites are ordinarily covered with adsorbed water, and that either high-temperature evacuation or irradiation can remove the water and reveal the activity. A closely related alternative (406) is the removal of the elements of water from surface hydroxyl groups either thermally or by irradiation, leaving residual ions or radicals which confer the catalytic activity. 

The chief point of interest in these results is that adsorbed hydrogen can in some way introduce a catalytic activity for the conversion. It is more feeble than that conferred by high-temperature evacuation, but it is stable toward air at ordinary temperatures. 

The following high temperature evacuation causes the densification of Si-O-Si bonds and forms ultra-micropores in the silica wall where only Ha can permeate. From the... 

As shown in Fig. 11.8, the powder is placed in sample holder in a pre-chamber and pretreated tmder normal pressure, or under reactant gases, and at high temperature, evacuated, and then transferred in the UHV chamber for surface analysis. 

The VPS overhead consists of steam, inerts, condensable and non-condensable hydrocarbons. The condensables result from low boiling material present in the reduced crude feed and from entrainment of liquid from the VPS top tray. The noncondensables result from cracking at the high temperatures employed in the VPS. Inerts result from leakage of air into the evacuated system. Steam and condensable hydrocarbons are condensed using an overhead water-cooled condenser. The distillate drum serves to separate inerts and non-condensables from condensate, as well as liquid hydrocarbons from water. Vacuum is maintained in the VPS using steam jet ejectors. 

Metallic Sr and Ba are best prepared by high-temperature reduction of their oxides with Al in an evacuated retort or by small-scale electrolysis of fused chloride baths. They have limited use as getters, and a Ni-Ba alloy is used for sparkplug wire because of its high emissivity. Annual production of Ba metal is about 20-30 tonnes worldwide and the 1991 price about 80-140/kg depending on quality. 

The most general preparative route to phosphides (Faraday s method) is to heat the metal with the appropriate amount of red P at high temperature in an inert atmosphere or an evacuated sealed tube ... 

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