Aluminas thermal decompositions

Pyrolysis Thermal decomposition of 1,1,1,2-tetrachloroethane produces tetrachloroethylene (by disproportionation), hydrogen chloride, and trichloroethylene via dehydrochlorination (111). The yield of the latter is increased in the presence of ferric chloride (112). Other catalytic materials include FeCl —KCl mixture (113), AlCl (6), the complex of AlCl with nitrobenzene (114), activated alumina (3), Ca(OH)2 (115,116), and NaCl (94). 

Chromia—alumina catalysts are prepared by impregnating T-alumina shapes with a solution of chromic acid, ammonium dichromate, or chromic nitrate, followed by gentie calciaation. Ziac and copper chromites are prepared by coprecipitation and ignition, or by thermal decomposition of ziac or copper chromates, or organic amine complexes thereof. Many catalysts have spiael-like stmctures (239—242). 

Ngo et al. [24] have shown that the thermal decomposition of ionic liquids, measured by TGA, varies depending on the sample pans used. Increased stabilization of up to 50 °C was obtained in some cases on changing from aluminium to alumina sample pans. 

Thermal decomposition was performed using a SDT Q-600 simultaneous DSC-TGA instrument (TA Instruments). The samples (mass app. 10 mg) were heated in a standard alumina 90 il sample pan. All experiments were carried out under air with a flow rate of 0.1 dm3/min. Non-isothermal measurements were conducted at heating rates of 3, 6, 9, 12, and 16 K/min. Five experiments were done at each heating rate. 

Contrary to the statements of Schulman etal. (81) and Taft et al. (77), there is very little similarity between thermal decomposition of aluminum alkoxides and dehydration of alcohols over aluminas. The thermal decomposition mechanism would not explain the skeletal isomerization occurring during the dehydration of 2-methyl-1-propanol (82). 

Activation by Thermal Decomposition of Metallic Oxides. The surface of alumina, AI2O3, may be activated by employing laser or ultraviolet irradiation to decompose AI2O3 (68). Decomposition of AI2O3 results in the generation of aluminum particles that are catalytic for electroless deposition of Cu (the first reaction probably is displacement deposition). 

It was reported early on that thermal decomposition above 110°C of Ir4(CO)i2 adsorbed on partially hydroxylated alumina gives carbonyl decomposition and renders metal parhcles of iridium below 1 nm [201]. 

Dioxins, 1,4-oxathiins, and 1,4-dithiins have often been prepared by elimination reactions from saturated analogs as described in CHEC-II(1996) <1996CHEC-II(6)447>. Since then, a synthesis of tetramethyl l,4-dithiin-2,3,5,6-tetracarboxylate 241 has been reported in low yield (12%) by thermal decomposition of the 1,4,2,5-dithiadiazine system 240 in refluxing o-dichlorobenzene in the presence of DMAD <1997J(P1)1157>. Recently, 2,6-divinyl-l,4-dithiin 68 has been isolated from the reaction of l,4-bis(4-bromobut-2-ynyloxy)benzene with an excess of alumina-supported sodium sulfide. The formation of 68 has been presumed to take place via cyclic sulfide 242 <2003S849>. 

Aluminum nitride UFPs have been synthesized by thermal decomposition from many kinds of precursor such as polyminoalanef l/ ) AIH(NR)] (50), aluminum polynuclear complexes of basic aluminum chloride (BAC) or basic aluminum lactate (BAL) (51), and (hydroxo)(succinato) aluminum(lll) complex, A1(0H)(C4H404) jfLO (52). These precursors were calcined under N2 or NH, gas flow. The calcination temperatures, which depend on the individual precursor, can be lower by 600-200°C than the 1700°C in ihe conventional carbothermal reduction method. The XRD measurements at intermediate stages of the calcination process showed the phase change from an amorphous state to a trace of y-alumina with very fine grains and finally to wurtzite-type AIN (51,52). Lowering the calcination... 

Evaporation of solutions of alumina in sulfuric acid yields crystals of A12(S04)3T6H20. If a group I sulfate is also present, the products are alums MA1(S04)2T2H20, in which aluminum exists as [Al(OH2)fi]3+. Analogous selenates but not tellurates have been prepared. Basic salts, e.g. Al2(OH)2(SO4)210H2O, and solids obtained from aluminum sulfate solutions above 100 °C also contain complex ions in which the coordination sphere of Al3+ is occupied by OH groups and/or water molecules rather than sulfate ions. Thermal decomposition of the hydrate A12(S04)3-16H20 yields practically anhydrous A12(S04)3 at 450 °C further decomposition to... 

S. Morooka, S. Yan, K. Kusakabe and Y. Akiyama Formation of Hydrogen-Permselective Si02 Membrane in Macropores of a-Alumina Support Tube by Thermal Decomposition of TEOS , J. Membrane Sci., 101 89-98 (1995). 

The catalytic CO oxidation by pure oxygen was selected as a model reaction. The Pt/alumina catalyst In the form of 3.4 mm spherical pellets was used. The CO used In this study was obtained by a thermal decomposition of formic acid In a hot sulphuric acid. The reactor was constructed by three coaxial glass tubes. Through the outer jacket silicon oil was pumped, while air was blown through the inner jacket as a cooling medium. The catalyst was placed in the central part of the tube. The axial temperature profiles were measured by a thermocouple moving axially in a thermowell. Gas analysis was performed by an infrared analyzer or by a thermal conductivity cell. [7]. 

Among monomeric metal carbonyls, Mo(CO)6, Cr(CO)6, Fe(CO)5, and Ni(CO)4 have been most studied. Their stepwise decomposition on the support may lead to the formation of grafted species. For example, Mo(CO)6 is first physically adsorbed onto hydroxylated alumina at room temperature [2, 62, 63, 68]. Thermal decomposition leads to the formation of adsorbed subcarbonyl species such as Mo(CO)s and then Mo(CO)3 at 373 K. Complete dccarbonylation at 573 K is observed upon oxidative addition of the metal on surface hydroxy groups ... 

At first sight, the catalytic behaviour and the surface properties of pyrochlore Al(OH,F)3 does not fit this model since the pyrochlore structure (cf Fig. 9(c)) is a more open one than the HTB-A1F3 structure. However, since aluminium hydroxofluoride is susceptible to thermal decomposition, it is in fact no longer pyrochlore Al(OH,F)3 under the temperature conditions employed for the catalytic reactions. Thus, the behaviour of this phase in heterogeneous catalytic halogen exchange can be explained by the presence of amorphous alumina which determines the surface characteristics at the initial stage. Consequently, this phase acts in a manner similar to alumina and not until the surface becomes completely fluorinated does it reach its full catalytic activity. 

The reaction is carried out by thermal decomposition of fluoroformates at temperatures in the range of 300-500 C in the presence of a catalyst. Suitable catalysts are platinum gauze. " V dluminum oxide, or platinum group metal impregnated alumina, where platinum shows the best results. Moreover iron, sled or oxides and halides of chromium. 

The poor selectivity of the thermal decomposition of polyolefins has promoted the development of catalytic cracking. Catalytic cracking lowers the pyrolysis process temperature and lowers the boiling temperature range of the resultant liquid products. The use of molecular sieves and amorphous silica-alumina catalysts for the cracking of waste polymers into a range of hydrocarbons has been widely studied (see Chapters 3-5, 7, 8). 

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