Catalysis noble metal-loading

Figure 12 shows the S mSat process based on published information. 120,179,180 SynSat process is considered to be an iimovation across the boundary between catalysis and reactor engineering . SynSat employs several different catalyst beds within a single reactor shell with intermediate by-product gas (H2S etc.) removal, and optional counter-current gas-flow. Catalysts A and B in Figure 9 are metal sulfide catalysts such as sulfided Ni-Mo. Catalyst C is a noble metal loaded on an acidic support such as zeolite. There is an intermediate gas removal between the beds of Catalysts B and C. Nearly all the sulfur compounds must be converted and removed as H2S on beds A and B before the fuel feed reaches the noble metal catalyst bed C. 

Although the SPE fuel cell can be considered to be a technological success, it could not be introduced into everyday commercial use because of its liigh cost, wliich is due mainly to the high cost of the ion-selective polymer membrane and the heavy loading of the noble metal catalysis needed for satisfactory operation. 

In 1960, Weisz, Frilette, and co-workers first reported molecular-shape selective cracking, alcohol dehydration, and hydration with small pore zeolites (6,7), and a comparison of sodium and calcium X zeolites in cracking of paraffins, olefins, and alkylaromatics (8). In 1961, Rabo and associates (9) presented data on the hydroisomerization of paraffins over various zeolites loaded with small amounts of noble metals. Since then, the field of zeolite catalysis has rapidly expanded,... 

Catalysis, whether by noble metals or enzymes, offers an opportimity to reduce environmental loads. Replacing a chemical process with an enzymatic one, Hoechst research lowered the elf value for making the valuable antibiotic intermediate 7-aminocephalosporin. The value fell from 30 to -0.7, a fourfold change Christ, 1996). Despite an increase in waste water, the fall in ELF reduced environmental costs of this step by 90%. 

There is considerable interest in the use of non-noble metals for fuel-cell catalysis, which is not surprising when one considers the cost of the noble metal Pt (at well over 900 US per troy ounce) and its noble metal alloying additions. In a PEM fuel cell using pure hydrogen at the anode, Pt loading requirements down to 0.05 mg Pt cm" are manageable. On the other hand, the eathode eomponent of the MEA still requires a loading of 1 mg Pt em in the best ease seenario, due to the slow kinetics of the ORR. 

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