Stabilised combustion of lean hydrogen–air mixtures in the presence of silica

The urgent need to transition out of our reliance on fossil fuels motivates the development of emission-free combustion technologies. Here we demonstrate a method to burn hydrogen, a fuel that can be produced with green electricity, in a packed bed of silica particles. The presence of silica particles prevents the significant increase in process temperature encountered in gas-flame arrangements, thereby enabling the conversion of hydrogen to heat while mitigating nitrogen oxide emissions. Partial combustion is observed in packed beds of silica particles below the gas-phase ignition temperature, suggesting that a heterogeneous combustion mechanism dominates at low temperatures. Above the gas-phase ignition temperature, silica particles prevent thermal runaway by acting as a heat sink, suppressing the OH • radical-producing chain branching reactions, and instead promoting the conversion of hydrogen to water vapour by a mechanism involving the hydroperoxyl intermediate. Radical quenching and recombination reactions on surfaces of silica particles further reduce the availability of free radicals during in-bed combustion. The combustion of hydrogen with solid particles of silica can easily be scaled up using a fluidised configuration, owing to the low cost and wide availability of quartz sand. We present a unique opportunity for the stabilised, nitrogen oxides-free conversion of hydrogen to heat, offering an economical and scalable solution for large-scale industrial heat production with important economic and environmental value.