TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The molecular sieve particles are ABW, AEI, AFT, AFX, APC, APD, ATN, ATT, ATV, AWW, BIK, BRE, CAS, CHA, DDR, EAB, EDI, ERI, GIS, GOO, ITE, JBW, KFI, LEV, LTA, MER, MON, NAT, PAU, PHI, RHO, RTE, RTH, THO, VNI, YUG, ZON, Linde type A, chabazite, erionite, silicon-containing aluminum phosphate-56, AEL, AFO, AHT, CGF, DAC, EPI, EUO, FER, HEU, LAU, MEL, MFI, MFS, MTT, NES, PAR, SFF, STF, STI, TER, TON, WEI, WEN, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57, SUZ-4, SSZ-13, SSZ-23, SSZ-25, SSZ-28, SSZ-32, SSZ-36, NU-87, silicalite, AFI, AFR, AFS, AFY, ATO, ATS, BEA, BOG, BPH, CAN, CON, CZP, DFO, EMT, FAU, GME, LTL, MAZ, MEI, MOR, MTW, OFF, OSI, RON, SAO, VET, Linde type L, beta zeolite, CIT-1, faujasite, mazzite, mordenite, ZSM-12, offretite, CLO, VFI, AET, CFI, cloverite and/or CTI-5, preferably SSZ-13. The molecular sieve particles: are microporous aluminosilicate particles; have an chabazite framework; have a silica to alumina molar ratio of greater than 25; and have an average particle size of 100-700 nm. The membrane has a carbon dioxide/methane ideal selectivity of at least 7% higher, or at least 9% higher at 65 psia and 35 degrees C than a comparable membrane with untreated molecular sieve particles.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The polymer which is compatible with the polymer to be employed in the mixed matrix membrane is (a) substituted or unsubstituted polysulfones, poly(styrene), styrene-butadiene copolymers, styrene-vinyl benzyl halide copolymers, polycarbonates, cellulosic polymers, polyamides, polyimides, polyethers, polyetherimides, polyetherketone, polyethersulfones, poly (arylene oxides), poly(esteramide-diisocyanate), polyurethanes, polyesters, poly(alkyl methacrylates), poly(acrylate), poly(phenylene terephthalate), polypyrrolones, polysulfides, poly(ethylene), poly(propylene), poly(butene-1), poly(4-methyl pentene-1), polyvinyls, poly(allyl), poly(benzobenzimidazole), polyhydrazides, polyoxadiazole, polytriazole, poly(benzimidazole), polycarbodiimides or polyphosphazenes, preferably polyimide or propanediol monoester crosslinkable. The crosslinked polymer continuous phase is (a), preferably polyimide or propanediol monoester crosslinkable. The treated molecular sieve particles are microporous aluminosilicate particles. EXAMPLE - Sieves (1 g) was added to a 100 ml round bottom flask and then dried under vacuum at 150 degrees C. Then 1-methyl-2-pyrrolidone (anhydrous) was added to the flask to yield a mixture (3-4 wt.%). A dry nitrogen purge was then started, and the sieves were dispersed. The flask was removed to a stir plate and 2,4,6-trimethyl m-phenylenediamine (0.98 g) and 3,5-diaminobenzoic acid (0.66 g) were added and stirred for 15 minutes. Then 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (4.81 g) was added. The mixture was then stirred for 12 hours to form a sieve/poly(amic acid) dispersion. Then 3-methylpyridine (1.1 ml) and acetic anhydride (9.6 ml) were added to the dispersion. The mixture was stirred for an additional 12 hours. The mixture was then precipitated in methanol and washed before collection via a high pressure filter unit. The collected solids were partially dried in a fume bonnet for several hours before being fully dried under vacuum at 200 degrees C for 8 hour. The dried solids were placed in a 100 ml round bottom flask, and a dry nitrogen purge was started. Then 1-methyl-2-pyrrolidone (anhydrous) (sufficient quantity) was added to the dry solids to form a mixture (20 wt.%). Then the temperature was increased to 100 degrees C and 1,3-propanediol (21.8 ml) was slowly added along with p-toluenesulfonic acid (2.8 mg). The temperature was then again increased to 140 degrees C and maintained for 12 hours. The mixture was again precipitated and washed in methanol before collection via high pressure filtration. The collected solids were dried in a bonnet for several hours before drying under vacuum at 75 degrees C for 48 hour to obtain treated sieves.