Abstract
MoO 3 Al 2O 3 containing 0.89 – 7.4% Mo and reduced at 950 °C by H 2 ( MoO 3 Al 2O 3 ;H 2;950 °) is Mo(0) Al 2O 3 . It has been studied and compared with Mo(0) Al 2O 3 prepared by Mo(CO) 6/dehydroxylated Al 2O 3;He,300 – 500 °;H 2,650 – 950 ° and found to be essentially equivalent in chemisorptive behavior. MoO 3 Al 2O 3 ;H 2,650 ° has also received some attention. The high purity alumina support treated H 2,950 ° becomes gray and is reduced by an amount representable as Al 2+ Al 3+ = 0.0012 . It is reoxidized to white material by O 2,800 ° but not by O 2,650 °. Content in O 2 must be kept below 0.03 ppm in the other gases if a clean metallic molybdenum surface is to be maintained for a reasonable period of time. The amount of CO adsorbed at 25 °C appears to be a measure of the percentage exposed of Mo(0) Al 2O 3 . If a molecule of CO is taken to occupy 1.5 sites, the percentage exposed of Mo varied from 25 to 58%. At 25 °C, H 2 is chemisorbed rapidly but rather weakly on Mo(0) Al 2O 3 , and at least two forms of activated adsorption exist at higher temperatures. Under the conditions of this work the Mo particles in the samples of Mo(0) Al 2O 3 are not carbide but rather, as evidenced by high resolution TEM and EXAFS, metallic bcc Mo.
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