Platinum-based catalytic converter

The utility of the platinum-catalyzed enyne cycloisomerization for the formal synthesis of Rosephilin, which is a member of prodiginine family of alkaloids, was reported by Trost and Doherty (Scheme 7.44) [94]. The critical step in the synthesis was the conversion of enyne 221 to bicyclic diene 222 by platinum-catalyzed enyne cycloisomerization. While palladium catalysis was found to be ineffective, the desired cyclopentene 222 was obtained when 221 was treated with the platinum-based catalytic system developed by Murai. Diene 222 was converted to tricyclic pyrrole intermediate 223 in an 11-step sequence. Since 223 had been converted to roseophilin 224, the entire procedure represented a formal synthesis of the alkaloid. 

Platinum is a relatively rare earth metal usually found with related metals osmium and iridium. While it has a number of industrial applications, its common consumer application is in catalytic converters. This application has actually increased platinum concentrations in roadside dust. The ability of platinum and its derivatives to kill cells or inhibit cell division was discovered in 1965. Platinum-based drugs, such as cisplatin, are used to treat ovarian and testicular cancer, and cancers of the head and neck, as well as others. Unfortunately, the toxic side effects of these agents often limit their usefulness. 

Reforming Both thermal and catalytic processes are utilized to convert naphtha fractions into high-octane aromatic compounds. Thermal reforming is utilized to convert heavy naphthas into gasoline-quality aromatics. Catalytic reforming is utilized to convert straight-run naphtha fractions into aromatics. Catalysts utilized include oxides of aluminum, chromium, cobalt, and molybdenum as well as platinum-based catalysts. 

Furthermore, lead compounds poison the platinum metal-based catalysts in catalytic converters, so that efforts to abate air pollution by automobiles through the use of catalytic converters (Section 8.4.2) are dependent on the use of lead-free fuels. Fuels of sufficiently high octane... 

ICP-MS is useful for analysis of catalysts from two perspectives The composition of the catalysts must be carefully controlled, particularly because the active elements are often expensive. The catalysts are often finely distributed in a substrate material so their concentration in the bulk material may be quite low. Second, catalysts, particularly those used in automotive catalytic converters, can be a significant source of platinum group elements in the environment. Re and Pt have been measured in catalysts by ICP-MS [193], Procedures for the analysis of used catalytic converter materials by ICP-MS have been reported [355]. Accurate measurements are essential for many of these applications so isotope dilution-based concentration calibration is commonly used. 

It should be noted that since sulfur is a poison for the platinum-based catalysts used for these changes, the feed for the catalytic reformer has to be essentially sulfur free. Sulfur is removed by passing the feedstock through a cobalt/molybdenum catalyst bed in the presence of hydrogen, Avhich can come from the catalytic reformer. Carbon-bound sulfur is converted to hydrogen sulfide (Eq. 18.30). 

The activities of fresh, supported platinum and base metal oxidation catalysts are evaluated in vehicle tests. Two catalysts of each type were tested by the 1975 FTP in four 600-4300 cm3 catalytic converters installed on a vehicle equipped with exhaust manifold air injection. As converter size decreased, base metal conversions of HC and CO decreased monotonically. In contrast, the platinum catalysts maintained very high 1975 FTP CO conversions (> 90% ) at all converter sizes HC conversions remained constant 70% ) at volumes down to 1300 cm3. Performance of the base metal catalysts with the 4300-cm3 converter nearly equalled that of the platinum catalysts. However, platinum catalysts have a reserve activity with very high conversions attained at the smallest converter volumes, which makes them more tolerant of thermal and contaminant degradation. 

FTP Emissions. The overall system performance during the 1975 FTP tests for HC and CO emissions as a function of catalytic converter volume is plotted in Figures 1 and 2 respectively. Emissions are expressed in g/mile of vehicle operation with the cold start, hot stabilized, and hot cycle emissions weighted as prescribed (3). There was a distinct difference in the performance of the base metal and platinum catalysts with decreasing converter volume. Both HC and CO emissions with base metal catalysts increased monotonically as converter volume was decreased. In contrast, when platinum catalysts were used, both HC and CO emissions decreased to a minimum at 1300 cm3 and then increased at the smallest volume. 

Unlike steel and the metals in batteries, catalyst family metals can be expected to be recycled on the basis of their value, as opposed to the dominance of their mass in fuel cell systems. For example, platinrrm family catalyst metals are currently quite successfully recycled from today s vehicles (including both platinum and rhodium). Bhakta (1994) notes that in today s catalytic converters, the catalyst is housed in a stainless steel canister. Therefore, to recycle the catalyst, special machines have been developed to slit the canisters and remove the catalyst. Given an estimated increase in the amormt of platinrrm group metals (PGMs) in fuel cells of 15 to over 200 times that of the catalytic converter for mobile fuel cell applications, it can be expected that similar technological development wotrld follow wide-scale deployment of fuel cells based onPGMs (Cooper 2003,2004a). 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

---