Preparation and Properties of Hydrothermally Stable γ‐Alumina Membranes

Supported mesoporous γ‐Al 2 O 3 membranes deteriorate and blister in steam‐containing environments at high temperatures. This deterioration led us to the development of a new type of supported γ‐Al 2 O 3 membrane with significantly improved stability under hostile conditions. Two measures were taken to achieve this result. First, the γ‐Al 2 O 3 itself was stabilized by an addition of 6 mol% La 2 O 3 to suppress pore growth of the mesoporous structure. Second, the adherence of the γ‐Al 2 O 3 membrane to the α‐Al 2 O 3 support was significantly improved by application of phosphate bonding between the membrane layer and the support, using an Al(H 2 PO 4 ) 3 precursor solution. Membranes applied without phosphate bonding were separated from the α‐Al 2 O 3 support during high‐temperature steam treatment, resulting in complete loss of separative properties. The newly developed membranes could be operated for 100 h at 600°C in H 2 O/CH 4 = 3/1 (by volume) at 2.5 MPa total pressure with no delamination or cracking in the membrane–support interface and with no significant pore growth in the γ‐Al 2 O 3 membrane.