High Site Concentration Research Articles

The influence of impregnating pH on the postnatal and steam reforming characteristics of a Co-Ni/Al 2O 3 catalyst

Bimetallic alumina supported Co-Ni catalysts were prepared by impregnation under low (2) and high (8) pH values. Support dissolution due to acid attack appeared to be responsible for the low BET surface area for catalyst obtained at pH 2. However, this low-pH catalyst possesses higher dispersion and superior metal surface area. This is ascribed to the charged-induced migration of metal cations towards the grain centre where adsorption sites are located as a result of the formation of positively charged alumina surface at low pH. Ammonia NH 3-TPD analysis showed that the surface of both catalysts was populated with weak Lewis acid sites though a higher site concentration was found on the high-pH catalyst. TEM images further revealed an eggyolk profile for the catalyst impregnated at pH 2 with metal species located in the particle interior; while in the catalyst synthesised at pH 8, the impregnant metal is concentrated around the external surface of the particle. XRD analysis of the catalysts before and after reduction indicates that the basic catalyst was more difficult to reduce probably because of higher metal aluminate content. This was further confirmed by the lower degree of reduction shown for this catalyst during the thermogravimetric TPR–TPO runs. Solid-state kinetic data of the catalyst calcination, reduction and oxidation conformed with the Avrami–Erofeev model. In particular, the ratios of the associated kinetic rate constants for calcination and oxidation parallel those obtained for the deactivation and steam reforming constants, respectively, in both catalysts. Thus, it may be possible to have an a priori knowledge of the comparative reaction and deactivation behaviour of different catalysts from the temperature-programmed kinetics of their nascent solid states.

Detection of estrogen receptor-like high affinity components by exposure of cytosols from mouse leydig cell tumor or male rat liver to chaotropic salts

Modifications of steroid-macromolecule interaction induced by so-called chaotropic salts were studied. When the cytosol from one of estrogen-independent mouse Leydig cell tumors was incubated with [ 3H]-estradiol (E 2), an unusual estrogen binding component was identified, with a relatively weak affinity for E 2 ( K d 10 −7 M). This binding could not be inhibited by diethylstilbestrol (DES). However, exposure of this cytosol to 0.4 M NaSCN resulted in the clear demonstration of high affinity binder for E 2 ( K d 10 −9 M). Furthermore, this high affinity binding with E 2 was inhibited by DES in a competitive manner. The quantitation of the binding sites revealed that the binding capacity at low concentrations of [ 3H]-E 2 (less than 10 nM) is higher in the presence of NaSCN than in the absence of NaSCN. Liver cytosol from noncastrated male rat was also found to contain E 2 binding component with a low affinity ( K d 10 −7 M) and a very high concentration of sites. The binding component with high affinity ( K d 10 −9 M) as well as a concomitant loss of the low affinity sites became detectable in 0.4 M NaSCN. Moreover, this association with E 2 was found to be competitively inhibited by DES ( K i 3 × 10 −9 M). The similar changes were elicited by the other chaotropic salt, NaClO 4. These observations suggest that the detection of receptor-like high affinity binder in chaotropic salts may be mediated by two different mechanisms: one is a formation of new high affinity binder, the other is a destruction of the unusual second binder. Furthermore, the easy demonstration of estrogen receptor in chaotropic salt which is not detectable in a conventional buffer system might indicate that careful consideration is required to decide the absence of receptor protein.