Alumina aging

Bayerite (P-Aluminum Trihydroxide). Bayerite is rarely found in nature. It has been synthesized by several methods A pure product is prepared by the Schm b method (3) in wliich amalgamated aluminum reacts with water at room temperature. Other methods include rapid precipitation from sodium alurninate solution by CO2 gassing, aging of gels produced by neutrali2ation of aluminum salts with NH OH, and rehydration of transition rlio alumina. 

Other countries have similar types, some classifications, as in Germany, are based on age-strength levels by standard tests (70). A product made in Italy and Prance known as Perrari cement is similar to Type V and is sulfate-resistant. Such cements have high iron oxide and low alumina contents, and harden more slowly. 

Catalyst composition and feed chloride have a noticeable impact on hydrogen yield. Catalysts with an active alumina matrix tend to increase the dehydrogenation reactions. Chlorides in the feed reactivate aged nickel, resulting in high hydrogen yield. 

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

The present study was initiated to understand the causes of large differences in perfonnance of various catalyst formulations after accelerated thermal aging on an engine dynamometer. In particular, we wished to determine whether performance charaderistics were related to noble metal dispersion (i.e. noble metal surface area), as previous studies have suggested that the thermal durability of alumina-supported Pd catalysts is due to high-temperature spreading or re-dispersion of Pd particles [20-25]. 

Figure 6. TEM images of cubic Pt nanoparticles supported on alumina (A) before reaction and (B) aged in NO/CH4 reaction mixture for 4h at 950 °C.

From late Miocene to present, subaerial arc-volcanic activity (calc—alkali rocks, andesite, tholeiitic and high alumina basalt) started associated with uplift of the Japanese Islands. This volcanic activity is different from that at middle Miocene age. 

Transient and Aging Phenomena in Anodic Alumina Films... 

Martinez C.E., McBride M.B. Aging of coprecipitated Cu in alumina Changes in structureal location, chemical form, and solubility. Geochim Cosmochim Acta 2000 64 1729-17369. 

Zeolites are formed by crystallization at temperatures between 80 and 200 °C from aqueous alkaline solutions of silica and alumina gels in a process referred to as hydrothermal synthesis.15,19 A considerable amount is known about the mechanism of the crystallization process, however, no rational procedure, similar to organic synthetic procedures, to make a specifically designed zeolite topology is available. The products obtained are sensitive functions of the reaction conditions (composition of gel, reaction time, order of mixing, gel aging, etc.) and are kinetically controlled. Nevertheless, reproducible procedures have been devised to make bulk quantities of zeolites. Procedures for post-synthetic modifications have also been described.20 22... 

Figure 4.12 Histogram from automated SEM-EDS particle analysis of 362 zeolite precursor particles. Particles were reacted from silica and alumina sources slowly combined and aged at (a) room temperature and (b) 75°C.

The Mobility of Silica in Steam. The reactivity of silica and silica-containing materials to steam has been assumed in the literature to explain several phenomena, a few of which are the sintering of silica (35), the aging of amorphous silica alumina cracking catalysts (36) and the formation of ultrastable molecular sieves (37). The basis of all these explanations is the interaction of siliceous materials with water to form mobile, low molecular weight silicon compounds by hydrolysis (38) such as ... 

Commercial catalysts. Two commercial catalysts made by Katalistiks b.v. were used. The first, EKZ-, was steam aged at 750 C for 18 hrs prior to use and the second, an EKZ-2 equilibrium catalyst from a European refinery, was heated at 300°C in air for 3 hrs prior to use. Alpha alumina, heated at 300 0 in air for 3 hrs, was used in order to estimate the contribution to conversion from thermal cracking. 

Although zircon was frequently used by the ancients for intagli, and although hyacinth and jargon were well known in the Middle Ages, the presence in these minerals of an unknown metal was not suspected until near the end of the eighteenth century. The earth zirconia was overlooked because of its great similarity to alumina, and it took the analytical skill of a Klaproth to detect it. 

Fio. 35. (a) The concept of complex oxide of zirconia, titania and alumina (AZT) and (b) its effect on thermal durability after thermal aging test at 1,000°C. 

In view of these considerations, a large amount of effort is reported in the scientific press on the development of a process to produce benzene from n-hexane by combined cyclization and dehydrogenation. w-Hexane has a low Research octane number of only 24.8 and can be separated in fair purities from virgin naphthas by simple distillation. Recently, an announcement was made of a process in the laboratory stage for aromatiza-tion of n-hexane (16). The process utilizes a chromia-alumina catalyst at 900° F., atmospheric pressure, and a liquid space velocity of about one volume of liquid per volume of catalyst per hour. The liquid product contains about 36% benzene with 64% of hexane plus olefin. The catalyst was shown to be regenerable with a mixture of air and nitrogen. The tests were made on a unit of the fixed-bed type, but it was indicated that the fluid technique probably could be used. If commercial application of this or similar processes can be achieved economically, it could be of immense help in relieving the benzene short-age. 

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