Scattered among the references, collected by Oregon State University, we sent you earlier to document the fact that Carbon Dioxide can be chemically reduced and converted into hydrocarbons and Oxygen, are mentions of Ruthenium, a Platinum Group metal, as a catalyst for Carbon Dioxide conversion reactions.
It is so efficient at splitting Carbon from CO2, and recombining it with Hydrogen to form the hydrocarbon fuel gas, and liquid fuel and chemical manufacturing raw material, Methane, that the reactions can be conducted in a low-heat, low-pressure environment, thus making the process of recycling Carbon Dioxide much more energy efficient.
The fact that it works, and works well, is confirmed herein by our own, US, patent examiners in their approval and issuance of Patent 4847231, parts of which we've reproduced below.
First, a brief excerpt from the text to emphasize the technology's efficiency:
"It is an object of this invention to provide a low pressure and low temperature process for the direct formation of methane from carbon dioxide and hydrogen by a heterogeneous catalytic gas phase reaction."
And, note, too, that this patent was issued in 1989. That's not as long ago as Paul Sabatier won the Nobel Prize for demonstrating that CO2 could be effectively recycled, but long ago enough that we should by now have stopped arguing about CO2 emissions from coal-use industries, and be well on our way to domestic liquid fuel self-sufficiency, through the conversion of our abundant coal and the recycling of coal's most abundant by-product.
Does anyone know why we are not?
PS: Ruthenium, though a somewhat uncommon Platinum Group metal, does have fairly wide-spread natural occurrence, and it can, according to web-based references, be synthesized in relative abundance in some nuclear reactors.
Excerpt (presented with overly-dense technical passages deleted. Interested readers are invited to explore through the link, but please do make note of the mention of Fischer-Tropsch coal-to-liquid conversion technology. It all ties in together. - JtM):
US Patent 4847231 - Mixed ruthenium catalyst
US Patent Issued on July 11, 1989
Inventors
- Gratzell, Michael
- Kiwi, John
- Thampi, Krishnan R.
Assignee
- Gas Research Institute
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Heterogeneous catalytic gas phase methane production from hydrogen and carbon dioxide is achieved directly at temperatures as low as 25° C. and at atmospheric pressures by use of a catalyst having a mixture of Ru and RuOx, wherein x is greater than 0 and equal to or less than 2, supported by a suitable metal oxide support. Photo-methanation using such catalysts having photo excitable support materials significantly increases methane production, yielding almost stoichiometrically quantitative amounts of methane according to Sabatier reaction.
2. Description of the Prior Art
Use of ruthenium as a hydrogenation catalyst on a titania support for Fischer-Tropsch reactions of CO and H2 to produce hydrocarbons, principally liquid hydrocarbons at elevated pressure and methane at atmospheric pressure, is known from a number of patents including U.S. Pat. Nos. 4,042,614; 4,477,595; 4,558,030; 4,567,205; and 4,619,910. The 4,047,614 and 4,477,595 patents teach suppression of methane formation in the Fischer-Tropsch reaction when using titania as opposed to alumina or carbon support material.
Nickel is a known hydrogenation catalyst for reforming of methane by reaction of carbon monoxide and hydrogen. U.S. Pat. No. 4,132,672 teaches addition of a small amount of iridium for improved conversion of hydrogen and carbon monoxide to methane.
The electrochemical reduction of carbon dioxide to methane on Ru electrodes is taught by K. W. Frese, Jr. and S. Leach "Electrochemical Reduction of Carbon Dioxide to Methane, Methanol, and CO on Ru Electrodes", Journal of the Electrochemical Society, Vol. 132, No. 1, pgs. 259-260, January 1985. This electrochemical reduction works only at low current densities and is not a selective as desired for methane.
Photoreduction of CO2 to methane and higher hydrocarbon in aqueous solution using Ru or Os colloids as catalysts is taught by Itamar Willner, Ruben Maidan, Daphna Mandler, Heinz Durr, Gisela Dorr and Klaus Zengerle, "Photosensitized Reduction of CO2 to CH4 and H2 Evolution in the Presence of Ruthenium and Osmium Colloids: Strategies to Design Selectivity of Products Distribution", J. Am. Chem. Soc., Vol. 109, No. 20, pgs. 6080-6086, 1987. This photoreduction reaction utilizes Ru metal as an electron transfer catalyst and consumes triethanol amine making the process commercially unattractive.
The Sabatier reaction:
CO2 + 4H2 > CH4 + O2
is a known important catalytic process which despite its favorable thermodynamics, has been difficult to achieve due to high energy intermediates imposing large kinetic barriers and the formation of side products is common. Investigations during recent years aimed toward improving the activity and selectivity of methanation catalysts has been reported, including Lunde, P. J. and Kester, F. L., J. Catal. 30, 423-429 (1973); Phyng Quack, T. Q. and Rouleau, D., J. appl. Chem. Biotechnol. 26, 527-535 (1976); Tomsett, A. D., Hagiwara, T., Miyamoto, A. and Inui, T., Appl. Catal., 26, 391-394 (1986); Solymosi, F., Erdoheli, A. and Bansagi, T., J. Catal. 68, 371-382 (1981); Weatherbee, G. D. and Bartholomew, C. H., J. Catal, 87, 352-362 (1984); and Inui, T., Funabiki, F., Suehiro, M. and Sezume, T., JCS Faraday Trans. 1, 75, 787-802 (1979). Although progress has been made, elevated temperatures of greater than 300° C. and pressures of greater than 1 atmosphere are still required for methane generation to proceed at significant rates and yields according to the Sabatier reaction.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a low pressure and low temperature process for the direct formation of methane from carbon dioxide and hydrogen by a heterogeneous catalytic gas phase reaction.
It is another object of this invention to provide catalytic gas phase methane production from hydrogen and carbon dioxide using a mixed Ru/RuOx catalyst wherein x is greater than 0 and less than or equal to 2.
It is yet another object of this invention to provide a process for the direct formation of methane from carbon dioxide and hydrogen providing a very selective yield of methane of greater than about 95 percent, and preferably greater than 99 percent.
It is still another object of this invention to provide a process for catalytic direct methanation of carbon dioxide and hydrogen using highly dispersed mixture of Ru/RuOx on a photoexcitable catalyst support material wherein the reaction rate is significantly enhanced through photoexcitation of the support material.
The catalyst used in the process of this invention is a mixed ruthenium catalyst of about 10 to about 90 percent Ru and about 10 to about 90 weight percent RuOx, wherein x is greater than 0 and less than and equal to 2. The mixed ruthenium catalyst is highly dispersed on a suitable metallic oxide support with Ru loading of about 1 to about 15 percent. Specifically, a mixed ruthenium catalyst of about 25 mole percent Ru and about 75 mole percent RuOx loaded onto a TiO2 support material, Ru loading of 3.8 percent, has been found to provide very selective, greater than 99 percent, yield of methane by direct reaction of CO2 and H2 at about ambient temperature and atmospheric pressure. Reaction rates may be enhanced in the order of four to five times by photoexcitation of the TiO2 support material under photoexcitation of the support material stoichiometry according to the Sabatier reaction continued to be greater than 99 percent at 1 atmosphere pressure and 46° C.
DESCRIPTION OF PREFERRED EMBODIMENTS
The process of this invention provides highly selective direct formation of methane from carbon dioxide and hydrogen according to the stoichiometry of the Sabatier reaction. High methane selectivity and yield is achieved at low temperatures and low pressures by use of a catalyst of a mixture of Ru and RuOx
The mixed ruthenium portion of the catalyst comprises about 10 to about 90 mole percent Ru and about 10 to about 90 mole percent RuOx wherein x is a number greater than 0 and less than and equal to 2. Preferred proportions of the mixed ruthenium catalyst are about 15 to about 35 mole percent Ru and about 65 to about 85 mole percent RuOx. Catalytic activity of the mixed ruthenium catalyst has been found to be superior to use of the fully reduced Ru or the unreduced RuO2 in the methanation reaction.
The support portion of the catalyst is a metal oxide which may be photoinsensitive for dark methanation or a semiconducting oxide for light activated methanation. highly dispersed on specific metal oxide support materials.
Loading of mixed Ru and RuOx on the support material in accordance with this invention should be about 1 to about 15 weight percent of the total mixed ruthenium/support material catalyst, preferably about 2.5 to about 7.5 weight percent. The powdered catalyst of this invention may be used in catalytically effective quantities and in any suitable manner known to the art for conduct of solid catalyst/gas phase reactions as known to the art. Hourly space velocities up to 100,000 h-1 have been employed and gave good conversions.
The direct reduction of carbon dioxide to methane by hydrogen according to the Sabatier reaction is highly selectively achieved by the process of this invention under low pressure and low temperature conditions. The process of this invention is carried out by passing gaseous carbon dioxide and hydrogen in contact with the mixed ruthenium/metallic oxide support catalyst of this invention. It is preferred that hydrogen be present in stoichiometric excess amounts, about 1 to about 5 times the stoichiometric amount required for the Sabatier reaction being suitable, about 2 to about 4 times stoichiometric hydrogen being preferred. The process for direct formation of methane from carbon dioxide and hydrogen according to this invention is carried out at low pressure, ambient up to about 10 atm, preferably ambient to about 3 atm. The process is suitably carried out at low temperatures below about 300° C. and preferably below 200° C., ambient to about 200° C. being suitable, about 50° to about 150° being preferred.
The process of this invention appears to proceed directly according to the Sabatier reaction. Analyses of gas mixtures during the process have found no evidence of formation of carbon monoxide and Fischer-Tropsch products, as further set forth specifically in Example II. This has been further confirmed by separate work showing that the hydrogenation of carbon monoxide using the catalyst of this invention requires much higher temperatures than the mild near ambient conditions suitable for the process of this invention. Still further, the direct conversion of carbon dioxide to methane according to the present process has been found to be very selective, the yield of methane being greater than 99 percent under many conditions. To the inventors' knowledge, the catalyst of this invention provides the first process for ambient room temperature conversion of carbon dioxide to methane.
Methane formation and carbon dioxide consumption strictly obeyed the 1:1 stoichiometry of the Sabatier reaction indicating that the catalyst operated in a very selective fashion. This was confirmed by gas chromotograph, mass spectrometry and high pressure liquid chromotography which failed to detect other byproducts. Particularly, the formation of carbon monoxide, methanol, formaldehyde, ethane and higher homologues can be excluded within the detection limit for these compounds which was at least 0.002 μmol per μmol of methane generated. There was no formation of formic acid or oxalic acid.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration,
* * * * * it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
Other References
- K W. Frese, Jr. and S. Leach "Electrochemical Reduction of Carbon Dioxide to Methane, Methanol, and CO on Ru Electrodes", Journal of the Electrochemical Society, vol. 132, No. 1, pp. 259-260
- Itamar Willner, R. Maidan, D. Mandler, Heinz Durr, G. Dorr and K. Zergerle, "Photosensitized Reduction of CO2 to CH4 and H2 Evolution in the Presence of Ruthenium and Osmium Colloids; Strategies to Design Selectivity of Products Distribution", J. Am. Chem. Soc., vol. 109, No. 20, pp. 6080-6086, 1987
- Lunde, P. J. and Kester, F. L., J. Catal. 30, 423-429 (1973)
- Phyng Quzck, T. Q. and Rouleau, D., J. Appl. Chem. Biotechnol. 26, 527-535 (1976)
- Tomsett, A. D., Hagiwara, T., Miyamoto, A. and Inui, T., Appl. Catal., 26, 391-394 (1986)
- Solymosi, F., Erdoheli, A. and Bansagi, T., J. Catal. 68, 372-381 (1981)
- Weatherbee, G. D. and Bartholomew, C. H., J. Catal., 87, 352-362 (1984)
- Inui, T., Funabiki, F., Suehiro, M. and Sezume, T., JCS Faraday Trans. 1, 75, 787-802 (1979)