oming an increas­ing­ly attrac­tive alter­na­tive as a feed­stock to make a range of fuels. Now chemists have invent­ed a new cat­alyt­ic process that could increase the yield of a clean form of diesel made from coal.

The method, described in the cur­rent issue of the jour­nal Sci­ence, uses a pair of cat­a­lysts to improve the yield of diesel fuel from Fis­ch­er-Trop­sch (F‑T) syn­the­sis, a near­ly cen­tu­ry-old chem­i­cal tech­nique for react­ing car­bon monox­ide and hydro­gen to make hydro­car­bons. The mix­ture of gas­es is pro­duced by heat­ing coal. Although Ger­many used the process dur­ing World War II to con­vert coal to fuel for its mil­i­tary vehi­cles, F‑T syn­the­sis has gen­er­al­ly been too expen­sive to com­pete with oil.

Part of the prob­lem with the F‑T process is that it pro­duces a mix­ture of hydro­car­bons — many of which are not use­ful as fuel. But in the recent research, Alan Gold­man, pro­fes­sor of chem­istry and chem­i­cal biol­o­gy at Rut­gers Uni­ver­si­ty, and Mau­rice Brookhart, pro­fes­sor of chem­istry at the Uni­ver­si­ty of North Car­oli­na at Chapel Hill, use cat­a­lysts to con­vert these unde­sir­able hydro­car­bons into diesel. The cat­a­lysts work by rear­rang­ing the car­bon atoms, trans­form­ing six-car­bon atom hydro­car­bons, for exam­ple, into two- and ten-car­bon atom hydro­car­bons. The ten-car­bon ver­sion can pow­er diesel engines. The first cat­a­lyst removes hydro­gen atoms, which allows the sec­ond cat­a­lyst to rearrange the car­bon atoms. Then the first cat­a­lyst restores the hydro­gen, to form fuel.

Diesel fuel pro­duced in this way has sev­er­al poten­tial advan­tages. Ordi­nary diesel con­tains mol­e­cules, called aro­mat­ics, that, when com­bust­ed, pro­duce par­tic­u­lates, Gold­man says. But the diesel formed by the new cat­a­lysts does not include aro­mat­ics, so it burns much clean­er, over­com­ing one of the major objec­tions to diesel fuel. This could lead to more vehi­cles using diesel engines, which are about 30 per­cent more effi­cient than gaso­line engines.

But the biggest advan­tage may be that the Unit­ed States has huge amounts of coal: “We have as much ener­gy in coal as the rest of the world has in oil. That’s enough to last us the next hun­dred years or so,” Gold­man says. Thus, a more effi­cient, and so less expen­sive method of con­vert­ing coal to diesel could sig­nif­i­cant­ly cut U.S. depen­dence on for­eign oil, and do so for a long time.

“When I saw this I thought it was real­ly a ter­rif­ic con­tri­bu­tion that could be very impor­tant,” says Richard Schrock, pro­fes­sor of chem­istry at MIT, who won the Nobel Prize in Chem­istry in 2005, with two oth­er sci­en­tists, for dis­cov­er­ing the type of cat­a­lyst used in the sec­ond step. Com­bin­ing two cat­a­lysts this way “is pret­ty rare,” he says. “You can’t just throw any two things togeth­er and expect to get the results you antic­i­pat­ed.”

Accord­ing to Robert Grubbs, pro­fes­sor of chem­istry at Cal­tech, who shared the Nobel prize with Schrock, “The key is find­ing cat­a­lyst sys­tems that are com­pat­i­ble, and will oper­ate at the tem­per­a­tures where you can do both process­es togeth­er.”

At this time, the new cat­alyt­ic method is still a proof-of-con­cept, and not ready for com­mer­cial use. For exam­ple, the sec­ond cat­a­lyst tends to break down. But Schrock says this prob­lem should be solv­able: “It’s the­o­ret­i­cal­ly pos­si­ble that this could become prac­ti­cal. I e‑mailed Alan Gold­man and said, ‘Look, we’ve got a lot of cat­a­lysts, and I can think of some things that might be ther­mal­ly more sta­ble.’ So I’m going to send him some cat­a­lysts, and he’s going to try them out.”

It also might be pos­si­ble to make cat­a­lysts that use prod­ucts from the first reac­tion to regen­er­ate them­selves. “Then the cat­a­lyst would­n’t die, and you could in fact keep the reac­tion going,” says Schrock.