Thermal sintering

Martinez-Arias, A., Fernandez-Garcia, M., Iglesia-Juez, A. et al. (2002) Influence of thermal sintering on the activity for CO-02 and CO-02-NO stoichiometric reactions over Pd/(Ce,Zr)0 c/Al203 catalysts, J. Soria, Appl. Catal. B 38, 151. 

Structural promotion A highly dispersed support can provide and (or) stabilize a high surface area of the catalyst supported by it. A typical example is ammonia synthesis where the thermal sintering of the iron catalyst is inhibited by alumina (although the phase configuration is different). 

Recent evaluations of S02 oxidation over noble metal catalysts (Pt, Pd, and Rh) have given some information on one particular secondary reaction. It was observed in car tests that S03 formation under the conditions of automobile exhaust is highly vulnerable to catalyst deactivation either by thermal sintering or by poisoning (78, 79). At the same time, the data indicated a lesser sensitivity of CO and hydrocarbon oxidation to catalyst aging. The results were confirmed in laboratory experiments (80). This is one example of preferential suppression of an undesirable side reaction. Obviously, the importance of a given poison on the different secondary reactions will vary widely with catalyst formulation and operating conditions. 

In addition to utilization of monoliths as a column material, two reports describing respectively silicate and synthetic organic polymer based monolithic frits were published recently [85,86], The conventional method of frit fabrication for a particle packed column usually involves thermal sintering of a section of the packing material, such as bare or octadecyl silica, using a heating device. This approach has several weaknesses such as the lack of control of the temperature and porous properties of the frit that decreases reproducibly of the fabrication process. 

Methanation catalysts are not usually deactivated by thermal sintering. The principal reason for any loss of activity is poisoning. Sulfur compounds will poison methanation catalysts, but sulfur is not present unless the low temperature shift catalyst is by-passed. The poisons most likely to occur under normal operating conditions are those originating from the carbon dioxide removal system that precedes the methanator. Carry-over of a small amount of liquid into the methanator is not serious. Large volumes of liquid will have a... 

The catalyst activity is assumed to be constant. Because of excellent temperature control achievable in tube-wall reactors, thermal sintering of the catalyst is less likely than in a fixed-bed reactor. Some methods of avoiding catalyst deactivation or reducing the deactivation rate for methanation are described by Mills and Steffgen (7). 

In conclusion, noble metals deposited on ceria-zirconia supports show both increased OSC and increased activity for NOx conversion, the clearer effect being obtained in dynamic conditions [102]. They are also more resistant than pure ceria to thermal sintering, since they are able to maintain a good activity even in a lOOO C durability test [102]. 

However, Inspection of Che morphology of the samples confirmed trends previously observed and offered possible reasons for the enhanced stability. As seen front Figure 13, glbbslce approximates to a faceted structure. 7-alumina has no distinct morphological features. In contrast UN5WAL shows clear evidence of needle like crystals. It is believed that these crystals, by offering a well defined structure with minimal inter particle contacts, leads to the minimisation of thermal sintering in the product. 

Importance and Manufacture of Thermal (Sinter, Melt) and Basic Slag (Thomas) Phosphates... 

The degradation of the catalytic activity with reaction time or thermal sintering was analytically studied by the determination of the specific surface area of the exposed palladium particles, by the chemical adsorption of carbon monoxide the distribution of palladium particles, by an electron microscope and the crystal imperfection, by X-ray diifraction analysis, and so on. 

Deactivation of CuO/ZnO/AljO, can be related to thermal sintering and Cu-Zn alloy formation. XRD data suggest that the presence of water, high temperature, and high partial pressure of hydrogen parti y reduce ZnO, enhancing formation of Cu-Zn alloy. 

In summary, the results show that deactivation of Cu-ZnO catalysts can occur by thermal sintering and by a solid phase reaction between Cu and the support. 

---