Carbon monoxide and methane dominate the product slate of most photocatalytic CO2 reduction studies. Although they are the two most-watched products, they behave very differently in an analytical train, and quantifying both accurately requires deliberately different handling.
CO binds strongly to many metal surfaces and can be consumed or generated by tubing, valves and pump materials. Use inert flow-path materials, and blank the whole train regularly. CO detectors, typically electrochemical or TCD-based, cross-respond to hydrogen, so verify selectivity in mixed H2/CO streams, which is exactly what a CO2 reduction reactor produces.
CH4 is chemically inert but light and volatile; it escapes through marginal seals faster than heavier gases. Its TCD response is modest, so the calibration curve needs enough points at the low end where photocatalytic production usually sits.
Calibrate each product independently at three or more points spanning your expected range. Carry out the calibration with the same carrier gas and moisture conditions as the experiment. Run a mixed standard to verify that the two products do not interfere in your actual configuration, single-gas calibration is not sufficient for a two-product stream.
Report both products with detection limits and the selectivity ratio with its uncertainty. When one product is below detection limit, state it explicitly rather than treating it as zero, because selectivity calculations are meaningless below the limit.
Perfectlight's online systems handle simultaneous multi-product monitoring; see gas detection products and the CO2 gas-phase reaction systems.
