A method of sealing defects in thin-film Pd-alloy composite membranes using commercially available glass frit powder is detailed. This technique involves application of a low melting point glass frit and in situ firing in inert gas to seal defects on the order of 1 mm in diameter. In this case, a glass frit with a melting point of 560 degrees C was found to produce stable seals at 520 degrees C during a 150 h stability test under pure hydrogen. Changing the feed mixture to 50% H-2, 25% Ar and 25% steam, however, caused softening and subsequent seal failure at 520 degrees C. However, stable operation was achieved with water gas-shift mixtures when the temperature was reduced to 400 degrees C. The seal is demonstrated to be very robust within ammonia decomposition membrane reactors. Even though the frit seal had direct contact with the catalyst bed, it was observed to be stable in an ammonia decomposition reactor at 520 degrees C. The catalytic membrane reactor obtained 98% conversion, producing above 99% purity hydrogen with a flux of 0.11 mol m(-2) s(-1) for 150 h with no signs of seal degradation. (C) 2016 Elsevier B.V. All rights reserved.