Abstract
We have investigated a series of supported and unsupported nickel and cobalt catalysts, principally using neutron vibrational spectroscopy (inelastic neutron scattering, INS). For an alumina supported Ni catalyst we are able to detect hydrogen on the metal for the first time, all previous work has used Raney Ni. For an unsupported Ni foam catalyst, which has similar behaviour to Raney Ni but with a much lower density, the spectra show that there are approximately equal numbers of (100) and (111) sites, in contrast to Raney Ni that shows largely (111) sites. The observation of hydrogen on cobalt catalysts proved to be extremely challenging. In order to generate a cobalt metal surface, reduction in hydrogen at 250–300 °C is required. Lower temperatures result in a largely hydroxylated surface. The spectra show that on Raney Co (and probably also on a Co foam catalyst), hydrogen occupies a threefold hollow site, similar to that found on Co(10bar{1}0). The reduced surface is highly reactive: transfers between cells in a high quality glovebox were sufficient to re-hydroxylate the surface.
Highlights
The Fischer–Tropsch (FT) process is a well-established chemical reaction that utilises synthesis gas (CO and H2), derived from natural gas, coal or biomass, to produce a wide-range of valuable hydrocarbon products [1, 2]
There is a resurgence of interest in the FT process for synthetic fuel production, because of the decreasing lifetime of crude oil, as well as a combination of other environmental and political factors [1, 3, 4]
Ruthenium is in limited supply and expensive and nickel catalysts result in large quantities of undesirable methane and can produce highly toxic nickel carbonyl compounds [1, 4]
Summary
The Fischer–Tropsch (FT) process is a well-established chemical reaction that utilises synthesis gas (CO and H2), derived from natural gas, coal or biomass, to produce a wide-range of valuable hydrocarbon products [1, 2]. Worldwide fuel and chemical production is based predominantly on crude oil, this is not sustainable. There is a resurgence of interest in the FT process for synthetic fuel production, because of the decreasing lifetime of crude oil, as well as a combination of other environmental and political factors [1, 3, 4]. Only iron and cobalt based catalysts are currently used industrially as FT catalysts [1, 2]. Iron based catalysts have a lower hydrogenation activity in comparison to cobalt and have a high selectivity towards the production of olefins and oxygenate products with promoters commonly added to further manipulate the product slate [1, 2]. The current demand for an alternative route to produce lower olefins (C2–C4), high value chemical feedstock, free from the use of crude
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