The quest to use alternative feedstocks like natural gas and biomass to produce fuels is spurring increasing interest in long-established Fischer-Tropsch synthesis (FTS). That technology typically relies on expensive cobalt-based catalysts. Now, researchers at the Heterogeneous Catalysis and Sustainable Chemistry group at the University of Amsterdam, The Netherlands, have developed an efficient cobalt-coated catalyst that promises to provide significant savings. It consists of a 1-nm-thick cobalt shell on an 8-nm iron oxide core. The catalyst synthesis method is low cost and scalable to the multi-ton quantities required for commercial FTS units, add the researchers.
Figure 1. Researchers optimized technique used decades ago for producing cobalt-doped iron-oxide particles for magnetic tapes. Illustration by Itamar Daube courtesy of Gadi Rothenberg.
In 2009, Total Gaz & Energies Nouvelles, Paris, contacted the group about developing a new FTS catalyst. The importance of scale-up influenced the direction of the work from the outset. "The scale-up constraint rules out all routes that require high sophistication, extreme temperatures, or expensive chemicals. Instead, we chose a classic coating method: surface nucleation of a cobalt phase onto iron oxide colloids. Rather appropriately, considering the age of the FTS process, we are revisiting the method that recording tape industries, such as 3M, BASF and TDK, used in the 1960s for producing magnetic tapes [Figure 1]," the researchers explain in a recent article in Angewandte Chemie.The two-step process produces spherical nanoparticles (with an average diameter of 10 nm) necessary for FTS, rather than high-aspect-ratio particles used in magnetic tapes. The method also ensures retention of the core-shell structure upon catalyst activation. "…We can say that the core-shell Fe-Co catalysts give sufficiently low CO2 and methane and sufficiently high alkenes and gasoline/diesel fractions to merit industrial interest," conclude the researchers.The next step in the development will involve scaling-up the process to provide enough catalyst for larger scale trials, notes Gadi Rothenberg, a professor at the university and leader of the research team. Total, which holds the patent on the technology, will decide timing of that and of any large-scale tests. The approach may have wider applicability, he believes. "…In principle it is good for making various core/shell catalysts, preferably using ferromagnetic components."Rothenberg adds that the work also underscores an important point: "…Using clever chemistry we chemists can avoid many problems that engineers rightfully complain about. In this case, the key to success was carrying out an economic analysis at the beginning of the project and making sure the development included only steps that are easy to scale-up."