Nickel-kieselguhr catalysts surface area

Nickel. As a methanation catalyst, nickel is presently preeminent. It is relatively cheap, it is very active, and it is the most selective to methane of all the metals. Its main drawback is that it is easily poisoned by sulfur, a fault common to all the known active methanation catalysts. The nickel content of commercial nickel catalysts is 25-77 wt %. Nickel is dispersed on a high-surface-area, refractory support such as alumina or kieselguhr. Some supports inhibit the formation of carbon by Reaction 4. Chromia-supported nickel has been studied by Czechoslovakian and Russian investigators. 

The catalysts used in these experiments included those already employed in the infrared measurements in addition to some others. The results are presented in Tables VI and VII along with some older measurements on Raney-nickel and a nickel-on-kieselguhr catalyst. These older measurements are slightly less accurate because the cyclohexane content of the reaction product was determined by mass spectrometry. The surface area of catalyst E was not determined hence, its reaction rates per unit of surface area could not be calculated. 

Catalytic tests in sc CO2 were run continuously in an oil heated flow reactor (200°C, 20 MPa) with supported precious metal fixed bed catalysts on activated carbon and polysiloxane (DELOXAN ). We also investigated immobilized metal complex fixed bed catalysts supported on DELOXAN . DELOXAN is used because of its unique chemical and physical properties (e. g. high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions). The effects of reaction conditions (temperature, pressure, H2 flow, CO2 flow, LHSV) and catalyst design on reaction rates and selectivites were determined. Comparative studies were performed either continuously with precious metal fixed bed catalysts in a trickle bed reactor, or discontinuously in stirred tank reactors with powdered nickel on kieselguhr or precious metal on activated carbon catalysts. Reaction products were analyzed off-line with capillary gas chromatography. 

Another common form of silica is diatomaceous earth, also known as kieselguhr. 6 This is a naturally occurring material composed of fossilized diatoms. It contains 70-90% Si02, has 0.2-0.7 im pores and a surface area of about 15-40 m /g. It is a common support for nickel catalysts used in large scale reactions. 

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