The integration of experiment and computational modelling in heterogeneously catalysed ammonia synthesis over metal nitrides

In this perspective we present recent experimental and computational progress in catalytic ammonia synthesis research on metal nitrides involving a combined approach. On this basis, it suggested that the consideration of nitrogen vacancies in the synthesis of ammonia can offer new low energy pathways that were previously unknown. We have shown that metal nitrides that are also known to have high activity for ammonia synthesis can readily form nitrogen vacancies on their surfaces. These vacancies adsorb dinitrogen much more strongly than the defect-free surfaces and can efficiently activate the strong N–N triple bond. These fundamental studies suggest that heterogeneously catalysed ammonia synthesis over metal nitrides is strongly affected by bulk and surface defects and that further progress in the discovery of low temperature catalysts relies on more careful consideration of nitrogen vacancies. The potential occurrence of an associative pathway in the case of the Co3Mo3N catalytic system provides a possible link with enzymatic catalysis, which will be of importance in the design of heterogeneous catalytic systems operational under process conditions of reduced severity which are necessary for the development of localised facilities for the production of more sustainable “green” ammonia

Health & safety: Laying down the law

Andrew Hopkins, the author of several bestselling books on process safety, argues in his latest release, "Failure to learn - lessons from Texas City", that the pendulum has swung too far away from prescriptive rules. Hopkins cites the 2005 explosion at Texas City, where 15 contractors died because the trailers they were working in were set up very close to the isomerization unit, which exploded after the raffinate splitter overfilled and hydrocarbons overwhelmed the blowdown stack, overflowed and ignited. There was a recommendation at Texas City that said that trailers should be sited at least 350 ft away from the process plant. Nevertheless, this was a recommendation and not a rule, and the risk assessment that should have been carried out was either done badly or not at all. However, not all agree with this view of the world. One such person is Peter Webb, health and safety manager for Basell Polyolefins in the UK. According to Webb, contrary to Hopkins' view that shoddy risk-assessment was to blame for BP's accident, the site already suffered from an over-proliferation of procedures and rules, which only confused staff. Web did not think the Texas City team used a risk assessment to justify what turned out to be a wrong decision, but they were confused because they already had too many rules. Hopkins points out that the problem here is not that there were too many rules, but that they were badly drafted