Pt- (and Co-) Promoted Molybdena-Alumina Catalysts: Analysis of the Impregnation Steps.

The equilibrium parameters for the adsorption of Mo(VI) on gamma-Al(2)O(3) and of Co(II) and Pt(IV) on MoO(3)/gamma-Al(2)O(3) were determined. The adsorption isotherms were performed from aqueous solutions of the corresponding precursors on two different alumina supports. According to the classification given by Giles, L-type-shaped, subgroup 2, adsorption curves were found for the system Mo on gamma-Al(2)O(3), L-type, subgroup 1, for the Pt on MoO(3)/gamma-Al(2)O(3), and S-type for Co on the MoO(3)/gamma-Al(2)O(3) system. Numerical calculations were carried out for all the isotherms to find the equilibrium parameters. These constants are being used to model the development of Pt, Co, and Mo profiles on MoO(3)/gamma-Al(2)O(3) or gamma-Al(2)O(3) extrudates, respectively, which belong to the new generation of noble-metal-MoO(3)/gamma-Al(2)O(3)-supported catalysts to be used in oil-refining processes. Copyright 2001 Academic Press.

The attentional system in brain injury survivors.

The present study was designed to check the model of attention proposed by Posner and Petersen (1990), in patients with traumatic brain injury. We analyzed a series of neuropsychological tests administered to these patients after they were discharged from the hospital. Scores obtained from this group were subjected to factor analysis. The results of this analysis could be characterized by four factors which accounted for 85.4% of the variance. According to our data, factor 1 (perceptual and motor speed) and factor 2 (vigilance and alertness) represent Posner's posterior attention system. Factor 3 (encoding) and factor 4 (shifting) represent Posner's anterior attention system (AAS), but we have to consider that the AAS is not only attention but is shared by other cognitive processes. The results also suggest that the attention system could be stable and could be defined independently from the type of patient and type of illness.