Hybrid Catalysts: Internal or External Configuration for Better Catalytic Performance?
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Mat. Res. Soc. Symp. Proc. Vol. 497 ©1998 Materials Research Society
The Pt-HY and Pt-HY/SA both contained 80 wt % of HY zeolite and 0.5 wt % of Pt. PtHY/SA sample contained in addition 10 wt % of SA, being a hybrid catalyst with "external" configuration, i.e. the micro-sized zeolite crystallites being embedded in the larger-sized particles of silica-alumina. Another reference sample, Pt-SA (Pt = 0.5 wt %, SA = 80 wt % and balance = bentonite) was also prepared. TABLE 1 Some physico-chemical properties of the HY zeolite and the cocatalyst used in the noctane conversion
HY SA
Particle size
(tm)§
BET surface area(m 2/g)
Pore diameter (10"9 m)
1-2 50-100
610 641
0.74 4.6
Surface Acidity* (MMol/g) (mmol/m 2) 0.92 0.32t
1.5 0.5
(§) determined by scanning electron microscopy; (*) measured by the NH 3 TPD technique; (t) weak acid sites when compared with those of the HY zeolite. ii) CI iyst testing and data computing a) The experimental set-up for the conversion of n-octane was identical to that described elsewhere [4, 8]. The reaction parameters were as follows: temperature = 172 'C-297 'C (445 K - 570 K); contact time = 0.13 to 2.5 h; partial pressure of n-octane = 0.02 atm; ratio of flow-rate of nitrogen (used as carrier gas) to flow-rate of hydrogen = 4/3; weight of catalyst = 0.625 g and duration of a run = 4h. The testing procedure and product analysis techniques used were identical to those described elsewhere [8, 9]. b) The total conversion of n-octane is defined as follows: - (NC)p] (NC)f
Ct(C atom%) v 100 [(NC)f
where (NC)f and (NC)p are the numbers of C atoms of n-octane in the feed and in the reactor outstream, respectively. For each catalyst at each reaction temperature, the experimental data for total conversion (much lower than 30 C atom %) were fit to a function, ffr), of the contact time t, by using a nonlinear regression algorithm. A third-order polynomial function was found with a good correlation factor (>0.98): Ct = a c+ b r 2 + ct 3 at a given reaction temperature T. The r = kPn general form of the rate equation was used, where k, P and n were the rate constant, the partial pressure of noctane and the order of the reaction, respectively. For accuracy reason, data of initial rates were used, resulting in the following equation for a reaction temperature T: K p-n x ro = p-n df ]
K=P~
0
~n•.
= Cx.r° xr
"IcT=O where C is a constant and ro is the initial rate of reaction. From these data, Arrhenius plots (ln ro versus 103/T) were obtained.
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II) STUDY OF THE N-HEPTANE ISOMERIZATION: i) Catalyst preparation and characterization: The HY materials were obtained by calcination in air at 550 'C overnight of the ammonium-Y zeolites [LZY-84 provided by U.O.P. in two forms: 1) 1/16" pellets (containing ca. 80 wt % of NH 4 Y and some non-defined large pore-sized binder), and 2) fine powder of NH 4Y]. a) Pt-Aliy -HY (i stands for "internal"): 10 g of HY zeolite pellets were immersed in a solution of x g of Al (NO 3)3. 9H 20 (Aldrich, ACS reagent) dissolved in 15 ml of water. x was calculate
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