Cordierite-based composite membrane coated on cordierite monolith

A method for forming a composite-membrane monolith, the method comprising:

• applying a cordierite-ceramic composite slip to surfaces of a cordierite monolith, the cordierite-ceramic composite slip comprising from 30 wt. % to 90 wt. % cordierite particles and from 10 wt. % to 70 wt. % ceramic particles other than cordierite particles to form a coated cordierite monolith, the surfaces of the monolith having a surface median pore size of from about 1 μm to about 15 μm, the cordierite particles having a cordierite median particle size from about 1 μm to about 3 μm and smaller than the surface median pore size, the ceramic particles having a ceramic median particle size from about 0.05 μm to about 0.5 μm and smaller than the cordierite median particle size, the weight ratio of the cordierite particles to the ceramic particles in the cordierite-ceramic composite slip being from 9:1 to 3:7;
• and
• firing the coated cordierite monolith to form the composite-membrane monolith, the cordierite-ceramic composite slip forming, during the firing, a cordierite-ceramic composite membrane as a composite having a thermal coefficient of expansion approximately equal to the thermal coefficient of expansion of the cordierite monolith and bonded directly to the surfaces of the cordierite monolith without any intervening layer between the cordierite monolith and the cordierite-ceramic composite, the cordierite-ceramic membrane having membrane surfaces with a membrane median pore size of 0.3 μm or less and with small pores having small-pore sizes from 0.05 μm to 0.1 μm, the membrane median pore size and the small pores providing polymer coatability to the membrane surfaces.