Converter catalyst

The protection of the environment implies the elimination of lead compounds, first of all because of their individual toxicities and second because these derivatives or their products of decomposition poison catalytic converter catalysts. 

Automotive Catalytic Converter Catalysts. California environmental legislation in the early 1960s stimulated the development of automobile engines with reduced emissions by the mid-1960s, led to enactment of the Federal Clean Air Act of 1970, and resulted in a new industry, the design and manufacture of the automotive catalytic converter (50). Between 1974 and 1989, exhaust hydrocarbons were reduced by 87% and nitrogen oxides by 24%. 

Gasoline must not contain phosphorus because it can degrade the activity of the catalytic converter catalyst. 

Fuel sulfur and phosphorus have been identified in contributing to problems with catalytic converter efficiency. Fuel sulfur does poison converter catalysts, but not as severely as lead. 

Ce02-supported noble-metal catalysts such as Pt, Pd and Rh are of interest because of their importance in the so-called three-way converter catalysts (TWC), designed to reduce emissions of CO, NOx and uncombusted hydrocarbons in the environment and to purify vehicle-exhaust emissions. Such catalysts are also of current interest in steam reforming of methane and other hydrocarbons. Conventional practical catalysts for steam reforming consist of nickel supported on a ceramic carrier with a low surface area and are used at high temperatures of 900 C. This catalyst suffers from coke formation which suppresses the intrinsic catalyst activity. Promoters such as Mo are added to suppress coke formation. Recently, Inui etal(l991) have developed a novel Ni-based composite... 

The promotion ability of cerium is attributed to its capability to form crystalline oxides with lattice defects, which may act as active sites [25]. In addition, the presence of cerium oxide in the catalyst improves its thermal stability and mechanical resistance [26]. Cerium is the most frequent additive used for preparation of the automobile converter catalyst that transforms carbon monoxide, hydrocarbons and nitrogen oxides [27,28]. 

Thus a variety of hydrocarbons, ranging from natural gas to coal, are used in methanol production. Regardless of the feedstock used to prepare the synthesis gas, it is necessary to remove sulfur so that the converter catalyst is not poisoned. Before natural gas or naphtha is reformed, the feedstock is desulfurized. In the partial oxidation and coal gasification processes, the feedstock is first oxidized and the resulting synthesis gas is desulfurized before entering the converter. 

Continuous measurement of OSC of the catalyst inserted in the converter is one of the simplest tool to monitor catalyst efficiency. This is known as the On-board diagnostic" (OBD). Sideris has recently reviewed the OBD technologies on the basis of the corresponding patent literature [103]. Even though other techniques are available (temperature sensors, specific sensors for CO, HC and NOx), OBD determined by means of O2 sensors remains the technique the most widely employed in car industry. This technique is based on the generation of periodic rich/lean perturbations monitored by two lambda sensors, one located upstream and the second downstream the converter. Catalysts that have good OSC considerably attenuate the upstream perturbation (with a significant time lag) while virtually dead... 

Catalytic Converters Catalysts are used in the exhaust systems of cars and trucks to aid fuel combustion. The exhaust passes through the catalyst, often in the form of beads coated with metals such as platinum or rhodium. Catalysts speed the reactions that change incompletely burned substances that are harmful, such as carbon monoxide, into less harmful substances, such as carbon dioxide. 

For both catalysts, the rate of increase in bed temperature was greater for smaller converter volumes although there was little difference between the 600- and 1300-cm3 converters. Catalyst temperature increased more rapidly with the platinum catalyst. Greater conversion efficiencies (Table V) and hence greater energy release rates were attained with this catalyst during warm-up cycles 1-5 of the FTP. The fraction converted by the platinum catalysts was maximum at the 1300-cm3 converter volume. Conversion efficiencies with the base metal catalysts increased continuously as volume increased. 

Pilot-plant operation is conducted usually at 300-325 C., 20-atmos-pheres pressure, with recycle of 3-4 volumes end gas/volume fresh feed. The latter is 1.8 to 2.0 H2 to 1 CO, prepared by oxidationof natural gas with oxygen-steam mixtures at 300—400 p.s.i. and 1200 C. The synthesis operation is in fixed fluidized bed that is, the bed of catalyst is suspended in the flowing gas with no carry-over of powdered catalyst outside the converter. Carry-over is completely avoided by the use of Aloxite filters in the expanded section of the top of the converter. Catalyst density in the fluidized bed is 60-80 pounds/cubic foot at the start. This density decreases during the first 2-14 days of operation to 10-20 pounds/cubic foot because of spalling of the catalyst induced by carbon formation. With a hydrogen-rich total feed gas, 1600 hours of continuous operation was achieved, and with a carbon dioxide-rich feed gas, only about 400 hours. Operation is limited to 1.5-2.5 linear feet/second gas velocity at this velocity conversions of 90-95% are obtained per pass so that multistage opera-... 

Renewal of all of the converter catalyst, including incorporation of some cesium-... 

Operate valves in gas fines to raise the converter catalyst bed temperatures as quickly as possible. 

The quartz and catalyst are collected in plastic bags or some other type of watertight containers stored until ready to return to the converter. Catalyst should be stored indoors or protected outdoors in unfavourable weather conditions. 

Catal dic converters led to the elimination of lead from gasoline, because lead poisons the converter catalyst. Similarly, sulfur poisons catalysts that may be used on future vehicles. Hence, the reduction of sulfur in gasoline and diesel fuel to ultra-low levels is a key requirement of Auto Oil n. 

Here again, as in the case of methanol steam reforming, the formation of methane under these conditions is prevented via the specificity of the shift-converter catalyst. For PEM fuel cells, further reduction in CO concentration is necessary (from about 0.5 percent down to less than 100 ppm). This is often carried out by way of catalytic preferential oxidation of CO in the presence of hydrogen with the addition of air at a flow rate that is a small multiple of the stoichiometric rate required for complete oxidation of the CO. 

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