Coke resistance

As shown in Table 2.1, the improved catalytic performance of alkaline-treated zeolites compared to the parent purely microporous counterparts has been demonstrated decidedly by different groups active in academia and in industry. The positive effect is reflected in the enhanced activity, selectivity, and/or lifetime (coking resistance) of the hierarchical systems. The examples listed embrace not only a variety of zeohte topologies (MFl, MOR, MTW, BEA, and AST) but also reactions involving hghter hydrocarbons as well as bulky molecules. This illustrates the potential of the desihcation treatment, although more work is to be done in optimizing the catalytic system for the wide variety of applications. 

Catalysts were prepared by deposition-precipitation method over a commercial CeOz. Among the catalysts, Ir/Ce02 exhibited a stable activity for 300 h time-onstream due to the prevention of metal sintering and coke resistance of highly dispersed Ir... 

MFl is typically the preferred zeolite due to its coking resistance, but other zeolites have been used, as detailed in the tables below. The mechanism of the dehydroaromatization is covered in greater detail in Chapter 15, as are representative processes such as UOP s Cyclar process [2, 91]. 

Solid oxide catalysts such as hexaaluminates and perovskites, in which an active metal catalyst is incorporated into a coke-resistant lattice, are effective for liquid hydrocarbon reforming due to their thermal stability over a broad-range of temperature. However, sulfur tolerance of those materials has yet to be demonstrated. 

From Tables III and V, it would appear that, fm the component of the feed which is more-rapidlv coking, the activity and the coke resistance of the catalyst change with the amount of that component in the feed. From Tables n and IV, conversely, fm the component of the feed which is less-rapidly coking, the behavior of the catalyst is apparently unchanged. 

Carbon dioxide was proposed as an oxidant in dehydrogenation of ethylbenzene over zeolite-supported iron oxide catalyst, which was highly dispersed in zeolite matrix. The dehydrogenation was mainly proceeded under the oxidative pathway in the presence of carbon dioxide. The presence of carbon dioxide contributed to remarkable enhancement not only in dehydrogenation activity of catedyst but also of its coke resistance. 

Coking resistant Nickel Catalysts for Hydrocarbon Steam Reforming Song Ruojun, Zhang Liangqu and Guo Shendu... 

The effect of suJfur poisoning on the coking tendency of alumina-supported ruthenium SNG catalyst has been studied. The clean KU/AI2O3 catalyst has exceptional coking resistance, and at 490 C and 25 atm, can tolerate steam to carbon ratios below stoichiometric (steam/carbori=0.6) with light naphtha before a continuous accumulation of carbon will occur. However, at this temperature (appropriate for SNG production), sulfur can adsorb on the active metal surfaces to a level which will cause a slow but steady accumulation of less reactive carbon. The critical sulfur coverage that adversely affected the steam to carbon ratio necessary to prevent continuous coking appears to fall just above one-half the maximum capacity of the catalyst. 

COKING-RESISTANT NICKEL CATALYSTS FOR HYDROCARBON STEAM REFORMING... 

Coking resistance data in Table 2 indicate that the amount of coke and/or carbon deposited on the unpromoted catalyst was about 24 time-t more than that on the promoted one after 24 h runs at H20/C=l, 6(X)°C, 1 atm. and SV(methane)=2000 h l. Fig. 1 shows that the amount of deposited coke and/or carbon on B was 2-7.6 times rtxne than that on A-01 at H20/C=2. 420-850"C and 30 kg/cni. ... 

Panja C, Saliba N, Koel BE (2000) Coking resistance of Pt-Sn alloys probed by acetylene chemisorption. Catal Lett 68 175... 

Xu J, Saeys M (2006) Improving the coking resistance of Ni-based catalysts by promotion with subsurface boron. J Catal 242 217... 

Urasaki, K., Sekine, Y., Kawabe, S., Kikuchi, E., and Matsukata, M. Catalytic activities and coking resistance of Ni/perovskites in steam reforming of methane. Applied Catalysis. A, General, 2005, 286 (1), 23. 

In the present work, the effect of Sn and the alkali metals (Li, Na and K) is presented. The main objective is to clarify their role in enhancing coking resistance of the resulting catalyst. 

Figure 4. Influence of the reduction temperature upon the activity and coking resistance of the catalysts.

Table 2 shows the process conditions applied in the pilot plant tests. Figure 1 gives the catalyst configurations. The two demetallization catalysts, KFRll and KFR 10 have a very high metal absorption capacity. KFR 11 is more metal tolerant than KFR 10. KFR 30 is a dual function catalyst for hydrodesulfurization and demetallization which is used as an intermediate stage in the catalyst system. KFR 50 is used as a downstream catalyst that has a high activity for desulfurization and is more coke resistant... 

In pretreatment of residual FCC feedstock, downstream catalysts with high coke resistance are essential to obtain sufficient catalyst life. 

The improved metal tolerance for upstream catalysts and improved coke resistance for downstream catalysts are the main success factors of the KFR catalyst system. 

High-temperature coking resistance is checked by the panel coker test where an aluminium plate, held at temperatures ranging from 275 to 350°C, is splashed with lubricant and the deposited coke is weighed and rated. This procedure has many variations including methods to measure the effect of the oxidising effect of fuel oil contamination on lubricant stability. 

Coking resistant Nickel Calalysts for Hydrocarbon Steam Reforming... 

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