Cerium Titanium Platinate As A Water Gas Shift Reaction Catalyst.

[NNadir]

The water gas shift reaction is currently the major source of hydrogen in the world.

The reaction is CO + H₂O <-> CO₂ + H₂.

In almost every case around the world - unremarked by dangerous fossil fuel apologists who hawk hydrogen cars - the source of the CO is a dangerous fossil fuel, often dangerous coal, but in the vast majority of cases dangerous natural gas.

In theory, though almost never in practice, CO can be obtained from the partial oxidation of biomass, assuming one doesn't have to burn a ton of dangerous fossil fuels to haul the biomass to a chemical plant.

The water gas reaction is exothermic and involves a small increase in entropy. This means that the Gibbs Free Energy of the reaction is negative and the reaction is spontaneous. That said, the decomposition of diamond (at atmospheric temperatures and pressures) to give graphite is also (in a thermodynamic sense) spontaneous, but this hasn't stopped the De Beers company from selling questionably obtained diamonds all over the world using the thermodynamically illiterate marketing slogan "Diamonds are forever!"

Although diamonds contained in all wedding rings are in fact, undergoing a change from the diamond allotrope into the graphite (pencil lead) allotrope, the reaction is extremely slow and diamond is said to be metastable. It will change, but will do so slowly that one can keep diamond around for a long time without noticing the change.

Many other things are metastable. Wood is metastable in the presence of oxygen.

Carbon monoxide, a dangerous fossil fuel waste that is routinely dumped in the atmosphere is metastable in the presence of water and/or oxygen. But it persists long enough to represent a very real pollution problem that is certainly responsible for hundreds of thousands of deaths each year.

If one would like to avoid compounds that are metastable one can add a catalyst. The distributed energy automotive industry - the source of much environmental misery - tries to reduce it's awful effects on the environment by inserting a catalyst between the dangerous fossil fuel waste generating engine and earth's atmosphere, limiting the destructive wastes to carbon dioxide and some particulates that lodge in people's lungs.

As a captive chemical - one that is used as an intermediate to produce other chemicals - carbon monoxide is quite useful. Most of the world's food supply depends on access to carbon monoxide captively used to make, as mentioned above, hydrogen.

Besides the partial oxidation of the dangerous natural gas constituent methane, another route to carbon monoxide is known as the Boudouard reaction. In this reaction carbon is oxidized by carbon dioxide to give two molecules of carbon monoxide. The carbon could be coal, or it could be char from biomass. Note that in this case the homogeneous catalyst is carbon dioxide which catalyzes the production of hydrogen from water and carbon without a combustion step taking place. All industrially produced combustion - including the combustion of biomass, including wood - produces carcinogenic compounds and distributes them in earth's atmosphere.

Common catalysts for carrying out the water gas shift reaction are supported zinc and copper. However these catalysts are limited by their turnover rate which is a measure of how many molecules of hydrogen can be made before the catalyst becomes useless. With "dirty" carbon, the kind produced from coal or biomass, these low turnover rates limit the economic viability of biomass derived CO in particular.

Indian chemists have reported a new platinum based catalyst however that reportedly has a high turnover rate, and a low platinum content, making it somewhat cheaper than it would be otherwise.

The title of the paper reporting this fact is "Nondeactivating Nanosized Ionic Catalysts for Water-Gas Shift Reaction."

Here is a link to an abstract and the publication itself if one has a subscription or is in a good scientific library:

http://pubs.acs.org/doi/abs/10.1021/ie900335k?prevSearch=%255Bauthor%253A%2BSudhanshu%255D%2BAND%2B%255Btitle%253A%2Bnanosized%255D&searchHistoryKey=">Ind. Eng. Chem. Res., 2009, 48 (14), pp 6535–6543

The authors of the paper report that they had previously designed a Cerium Lanthanum Platinate catalyst, but while the catalyst has a high turnover rate, it was not as high as the new titanium based catalyst. The authors claim - although it is probably not the case - that the new titanium based catalyst has an infinite turnover. Probably they have not tested it for a long enough time for it to fail, but still that is, in itself, pretty good news. The reason, they speculate, that the catalyst has such a high turnover rate has to do with the lower oxidation state (II) of Pt in this catalyst as well as the acidity of titanium as compared to the more basic lanthanum. Acidity prevents the formation of carbonates, and carbonate formation is mechanistically important in the deactivation of catalysts.

Esoteric but cool paper.