Plasma Catalyst Interactions

To gain further insight into how the plasma and catalyst interact in this system, we performed some characterisation of the catalysts after a period of treatment in the plasma environment using BET (Brunauer, Emmett and Teller) surface area analysis, SEM (scanning electron microscopy) investigation of the surface morphology, elemental analysis and ATR-IR (attenuated total reflection Infrared) spectroscopy... 

At the same time, one should notice that the real catalysts are applied in the gas/liquid environments at usually an increased temperature so that dynamic structural evolution of a real catalyst would not be probed in a conventional electron microscope. To bridge the gap, in situ environmental electron microscope is developed by placing a micoreactor inside the column of an electron microscope to follow catalytic reaction processes [58-62], However, the specimen in an in situ TEM may suffer from interaction with ionised gas (plasma), making the interpretation of in situ TEM study of catalytic reaction more complicated. Characterisation of static, post-reaction catalysts is still the most commonly used. Well-designed model catalysts and reasonable interpretation of the results are essential to a successful study. 

As noted previously, for heparin to exert its anticoagulant effect, a plasma cofactor, antithrombin III, is needed. It has been proposed that heparin acts as a catalyst to cause a marked increase in the rate of interaction between AT-III and serine proteases like thrombin and Factor Xa (B4). Some uncertainty still exists as to whether the binding of heparin to the inhibitor or the enzyme or to both is the key step (P6). 

Fig 6 shows the single-stage system, which is referred to as plasma-driven catalysis [77]. In the PDC process, catalysts arc directly placed in the NTP reactor. These catalysts arc activated by NTP at low temperature region, where the thermal catalysis docs not occur. The shape of catalyst is cither of honeycomb, foam or pellet. In contrast to the PEC system, all reactions of gas-phase, surface and their interaction lake place simultaneously. In this sense, it is quite complicate to understand and optimize the chemical reactions in the PDC system. In an early USA patent, Henis proposed a PDC reactor for NO.r removal. Figure 7 shows the schematic diagram of the PDC reactor proposed by Henis [78], which is quite similar to those used in recent studies. The gases arc introduced to the reaction zone through the contact materials for heat transfer purpose. The catalysts listed in the patent are alumina, zirconium silicate, cobalt oxide, Thoria, activated carbon, molecular sieves, silica gel etc. 

In contrast to the PEC system, catalysts are placed in the plasma zone in the PDC system, so a lot more complicated interactions are expected between the plasma and the surface of catalyst. Again, the PDC system has both characteristics of gas-phase NTP and catalytic process. Table 5 summarizes the difference between the NTP alone and the PDC system. One of the important advantages of the PDC system over the conventional NTP reactors is the high energy efficiency (see Fig.3). Another important characteristic of the PDC system is its kinetics. Determination of reaction kinetics is useful to understand the overall characteristics of the chemical reaction in question. The influence of gas residence time (i.e. GHSV) is not observed both the NTP alone and the PDC. 

Mance, AM., Waldo, R.A and Dow, A.A, Interaction of Electroless Catalysts With Plasma-Oxidized Surfaces of Polystyrene Based Resins , J. Electrochem. Soc., 136(6), 1667-1671 (1989)... 

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