the catalyst of the invention comprises palladium nanoparticles , support nanoparticles , and a titanium zeolite having a particle size of 2 microns or greater . titanium zeolites comprise the class of zeolitic substances wherein titanium atoms are substituted for a portion of the silicon atoms in the lattice framework of a molecular sieve . such substances , and their production , are well known in the art . see for example , u . s . pat . nos . 4 , 410 , 501 and 4 , 666 , 692 . suitable titanium zeolites are those crystalline materials having a porous molecular sieve structure with titanium atoms substituted in the framework . the choice of titanium zeolite employed will depend upon a number of factors , including the size and shape of the olefin to be epoxidized . particularly preferred titanium zeolites include the class of molecular sieves commonly referred to as titanium silicalites , particularly “ ts - 1 ” ( having an mfi topology analogous to that of the zsm - 5 aluminosilicate zeolites ), “ ts - 2 ” ( having an mel topology analogous to that of the is zsm - 11 aluminosilicate zeolites ), “ ts - 3 ” ( as described in belgian pat . no . 1 , 001 , 038 ), and ti - mww ( having a topology analogous to that of the mww aluminosilicate zeolites ). titanium - containing molecular sieves having framework structures isomorphous to zeolite beta , mordenite , zsm - 48 , zsm - 12 , sba - 15 , tud , hms , and mcm - 41 are also suitable for use . ts - 1 and ti - mww are particularly preferred . the titanium zeolites preferably contain no elements other than titanium , silicon , and oxygen in the lattice framework , although minor amounts of boron , iron , aluminum , sodium , potassium , copper and the like may be present . the titanium zeolites having a size of 2 microns or greater may be a large particle size titanium zeolite produced , for example , according to the procedure described in u . s . pat . no . 7 , 399 , 726 . preferably , the titanium zeolite is produced by spray drying , pelletizing or extruding the titanium zeolite to form large particle titanium zeolite having a size of 2 microns or greater . if spray dried , pelletized or extruded , the titanium zeolite may additionally comprise a binder or the like and may be molded , spray dried , shaped or extruded into any desired form . preferred binders include silica , alumina , and titania . the catalyst of the invention also comprises palladium nanoparticles and support nanoparticles . the palladium nanoparticles of the invention have an average crystallite size less than 100 nm , preferably from 0 . 1 to 50 nm , and most preferably from 1 to 20 nm . preferably , the amount of palladium present in the catalyst will be in the range of from 0 . 01 to 20 weight percent , more preferably from 0 . 1 to 10 weight percent . the support nanoparticles are support materials that have an average crystallite size less than 200 nm , preferably from 0 . 5 to 100 nm , and most preferably from 3 to 60 nm . the support material is preferably an inorganic oxide of group 2 , 3 , 4 , 5 , 6 , 13 , or 14 elements . preferred supports include silica , alumina , silica - aluminas , titania , zirconia , niobia , tantalum oxides , molybdenum oxides , tungsten oxides , amorphous titania - silica , amorphous zirconia - silica , amorphous niobia - silica , and the like . particularly preferred supports include titania , zirconia , niobia , silica , alumina , tantalum oxide , and mixtures thereof . titania is most preferred . preferably , the support nanoparticle has a surface area in the range of about 1 to about 700 m 2 / g , most preferably from about 10 to about 500 m 2 / g . preferably , the pore volume of the support nanoparticle is in the range of about 0 . 1 to about 4 . 0 ml / g , more preferably from about 0 . 5 to about 3 . 5 ml / g , and most preferably from about 0 . 8 to about 3 . 0 ml / g . the palladium nanoparticles are deposited on the support nanoparticles to form supported palladium nanoparticles . the supported palladium nanoparticles can be produced by any known method . for instance , the palladium and support nanoparticles can be produced together by passing an aerosol comprising a mixture of palladium powder and a support ( or a support precursor ) through a plasma torch to vaporize the palladium powder and support to produce the supported palladium nanoparticles , which comprise palladium nanoparticles supported on support nanoparticles . see , e . g ., u . s . pat . no . 5 , 989 , 648 . the supported palladium nanoparticles are then preferably dispersed in a solvent , and deposited on the titanium zeolite or the carrier to form the catalyst of the invention . preferably , the supported palladium nanoparticles are transported from the supported palladium nanoparticle formation step by means such as a mechanical pump to the dispersing solvent . dispersing solvents useful in the present invention include any aqueous or nonaqueous liquid . suitable dispersing solvents include , but are not limited to , water , oxygenated hydrocarbons such as alcohols , ethers , esters , and ketones , aromatic and aliphatic hydrocarbons such as toluene and hexane , halogenated hydrocarbons such as methylene chloride and chlorobenzene , nitriles such as acetonitrile , and alkylalkanolamines such as 2 - dimethylaminoethanol . aqueous solvents are particularly preferred . the dispersing solvent may be a pure solvent or a mixture of solvents and may contain additional ingredients , including dispersing aids . suitable dispersing aids include inorganic and organic soluble materials , such as soluble polymers , surfactants , insoluble particulates , acids , bases , and salts . surfactants include , but are not limited to , alkylcarboxylic acid salts , alkylsulfonic acid salts , alkylbenzenesulfonic acid salts , alkyl sulfates , alkyl phosphonates , amines , aminoalkylsulfonic acid salts , aminoalkyl phosphates , alkylamine salts , and tertiary ammonium salts of fatty acids or aromatic acids . preferably , the dispersing aid is a soluble polymer such as poly - n - vinylpyrrolidone , polyvinyl alcohol , polyvinyl acetate , polyacrylic acid , polymethacrylic acid , polyacrylamide , polyvinylimidazole and polyvinylpyrazole poly ( vinylpyrrolidone ), polyalkylene glycols , poly ( propylene oxide ), and polydialkylsiloxane . preferably , the amount of dispersing aid in the solvent can be from 0 to 50 %, preferably 0 to 20 %, and more preferably 0 to 5 %. the supported palladium nanoparticles are deposited on the titanium zeolite ; or the supported palladium nanoparticles are deposited on a carrier having a particle size of 2 microns or greater . the carrier is any carrier having a particle size of 2 microns or greater , more preferably 5 microns or greater , and most preferably from 5 microns to 100 microns . the carrier is preferably a porous material . carriers are well - known in the art . for instance , the carrier can be inorganic oxides , clays , carbon , and organic polymer resins . preferred inorganic oxides include oxides of group 2 , 3 , 4 , 5 , 6 , 13 , or 14 elements . particularly preferred inorganic oxide carriers include silica , alumina , silica - aluminas , titania , zirconia , niobium oxides , tantalum oxides , molybdenum oxides , tungsten oxides , amorphous titania - silica , amorphous zirconia - silica , amorphous niobia - silica , and the like . preferred organic polymer resins include polystyrene , styrene - divinylbenzene copolymers , crosslinked polyethyleneimines , and polybenzimidazole . suitable carriers also include organic polymer resins grafted onto inorganic oxide carriers , such as polyethylenimine - silica . preferred carriers also include carbon . particularly preferred carriers include titania , zirconia , niobia , silica , alumina , silica - alumina , tantalum oxide , titania - silica , zirconia - silica , niobia - silica , and mixtures thereof . titania is particularly preferred . the supported palladium nanoparticles may be deposited on the carrier ( or titanium zeolite ) by any suitable method , including impregnation , adsorption , precipitation , or the like . if deposited on a carrier , the supported palladium nanoparticle - on - carrier material is mixed with titanium zeolite to form the catalyst of the invention . preferably , the catalyst of the invention also contains one or more additional metals including lead , bismuth , zinc , copper , tin , or other noble metals such as gold , silver , platinum , iridium , ruthenium , or osmium . lead , platinum and gold are especially preferred . the typical amount of additional metal present in the catalyst is preferably in the range of from about 0 . 01 to 10 weight percent , more preferably 0 . 01 to 2 weight percent . the one or more additional metals may be added into the catalyst during the nanoparticle formation step , e . g ., vaporizing an aerosol comprising a mixture of palladium powder , additional metal ( s ) powder ( or an alloy of palladium and one or more additional metals , e . g ., a pd - metal alloy such as pd — pb alloy ) and support ( or support precursor ) in a plasma torch . the one or more additional metals may be added into the catalyst by adding one or more additional metal compounds into the supported palladium nanoparticle dispersion , which is then added to the carrier or titanium zeolite as described above . also , the one or more additional metals may be added to the catalyst by a post - treatment with one or more additional metal compounds or may be added to the carrier or titanium zeolite prior to deposition of the supported palladium nanoparticle . suitable metal addition methods include impregnation ( e . g ., by incipient wetness , etc . ), adsorption , ion - exchange , deposition - precipitation , or other incorporation methods . suitable additional metal compounds include nitrates , carboxylates ( e . g ., acetate ), halides ( e . g ., chlorides , bromides , iodides ), cyanides , and sulfides . for example , lead nitrates and carboxylates are particularly preferred . the catalyst may be encapsulated in a polymer , for example , polystyrenics , polyolefins , polyureas , polyacrylics , polyurethanes , polyesters , polyamides , fluorinated polymers , polysaccharides , polypeptides , polynucleotides , and mixtures thereof . see u . s . pat . nos . 6 , 958 , 255 and 7 , 030 , 255 . the catalyst may also be additional comprise a thiol , where the thiol is tethered to the carrier or to the titanium zeolite . see , e . g ., u . s . pat . nos . 7 , 453 , 003 and 7 , 501 , 532 . the epoxidation process of the invention comprises contacting an olefin , oxygen , and hydrogen in the presence of the catalyst . suitable olefins include any olefin having at least one carbon - carbon double bond , and generally from 2 to 60 carbon atoms . preferably the olefin is an acyclic alkene of from 2 to 30 carbon atoms ; the process of the invention is particularly suitable for epoxidizing c 2 - c 6 olefins . more than one double bond may be present , as in a diene or triene for example . the olefin may be a hydrocarbon ( i . e ., contain only carbon and hydrogen atoms ) or may contain functional groups such as halide , carboxyl , hydroxyl , ether , carbonyl , cyano , or nitro groups , or the like . the process of the invention is especially useful for converting propylene to propylene oxide . oxygen and hydrogen are also required for the epoxidation process . although any sources of oxygen and hydrogen are suitable , molecular oxygen and is molecular hydrogen are preferred . epoxidation according to the invention is carried out at a temperature effective to achieve the desired olefin epoxidation , preferably at temperatures in the range of 0 - 250 ° c ., more preferably , 20 - 100 ° c . the molar ratio of hydrogen to oxygen can usually be varied in the range of h 2 : o 2 = 1 : 10 to 5 : 1 and is especially favorable at 1 : 5 to 2 : 1 . the molar ratio of oxygen to olefin is usually 2 : 1 to 1 : 20 , and preferably 1 : 1 to 1 : 10 . a carrier gas may also be used in the epoxidation process . as the carrier gas , any desired inert gas can be used . the molar ratio of olefin to carrier gas is then usually in the range of 100 : 1 to 1 : 10 and especially 20 : 1 to 1 : 10 . as the inert gas carrier , noble gases such as helium , neon , and argon are suitable in addition to nitrogen and carbon dioxide . saturated hydrocarbons with 1 - 8 , especially 1 - 6 , and preferably with 1 - 4 carbon atoms , e . g ., methane , ethane , propane , and n - butane , are also suitable . nitrogen and saturated c 1 - c 4 hydrocarbons are the preferred inert carrier gases . mixtures of the listed inert carrier gases can also be used . specifically in the epoxidation of propylene , propane can be supplied in such a way that , in the presence of an appropriate excess of carrier gas , the explosive limits of mixtures of propylene , propane , hydrogen , and oxygen are safely avoided and thus no explosive mixture can form in the reactor or in the feed and discharge lines . preferably , epoxidation is carried out in the liquid ( or supercritical or subcritical ) phase . it is advantageous to work at a pressure of 1 - 100 bars and in the presence of one or more solvents . suitable solvents include any chemical that is a liquid under reaction conditions , including , but not limited to , oxygenated hydrocarbons such as alcohols , ethers , esters , and ketones , aromatic and aliphatic hydrocarbons such as toluene and hexane , nitriles such as acetonitrile , liquid co 2 ( in the supercritical or subcritical state ), and water . preferable solvents include liquid co 2 , nitriles , alcohols , ketones , and mixtures thereof , and mixtures of these solvents with water . preferred nitriles include acetonitrile and other nitriles with appreciable water solubility . preferred alcohols include lower aliphatic c 1 - c 4 alcohols such as methanol , ethanol , isopropanol , and tert - butanol , or mixtures thereof . fluorinated alcohols can be used . it is particularly preferable to use mixtures of the cited alcohols with water . the process may be performed using a continuous flow , semi - batch or batch mode of operation . when a liquid reaction medium is used , the catalyst is preferably in the form of a suspension or fixed - bed . if epoxidation is carried out in the liquid ( or supercritical or subcritical ) phase , it is advantageous to use a buffer . the buffer will typically be added to the solvent to form a buffer solution . the buffer solution is employed in the reaction to inhibit the formation of glycols or glycol ethers during epoxidation . buffers are well known in the art . buffers useful in this invention include any suitable salts of oxyacids , the nature and proportions of which in the mixture , are such that the ph of their solutions may range from 3 to 10 , preferably from 4 to 9 and more preferably from 5 to 8 . suitable salts of oxyacids contain an anion and cation . the anion portion of the salt may include anions such as phosphate , monohydrogenphosphate , dihydrogenphosphate , sulfate , carbonate , bicarbonate , carboxylates ( e . g ., acetate , phthalate , and the like ), citrate , borate , hydroxide , silicate , aluminosilicate , or the like . the cation portion of the salt may include cations such as ammonium , alkylammoniums ( e . g ., tetraalkylammoniums , pyridiniums , and the like ), alkali metals , alkaline earth metals , or the like . examples include nh 4 , nbu 4 , nme 4 , li , na , k , cs , mg , and ca cations . more preferred buffers include alkali metal phosphate and ammonium phosphate buffers . buffers may preferably contain a combination of more than one suitable salt . typically , the concentration of buffer in the solvent is from about 0 . 0001 m to about 1 m , preferably from about 0 . 001 m to about 0 . 3 m . the buffer useful in this invention may also include the addition of ammonia gas to the reaction system . the following examples merely illustrate the invention . those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims . ts - 1 can be made according to any known literature procedure . see , for example , u . s . pat . no . 4 , 410 , 501 , direnzo , et . al ., microporous materials ( 1997 ), vol . 10 , 283 , or edler , et . al ., j . chem . soc ., chem . comm . ( 1995 ), 155 . ti - mww can be made according to wu et al ., j . phys . chem . b , 2001 , 105 , p . 2897 . the aqueous dispersions of supported palladium nanoparticles are produced by sdcmaterials , inc . comparative catalyst 1a ( pd / tio 2 ): a solution of nitric acid ( 5 ml , 5 m ), deionized water ( 3 ml ), and an aqueous solution of palladium nitrate ( 0 . 535 g , 20 . 64 wt . % pd ) is added by incipient wetness to spray dried titania ( 10 g , 40 micron size , calcined in air at 700 ° c .). the solids are calcined in air in a muffle furnace by heating at 10 ° c ./ min to 110 ° c . for 4 hours and then at 2 ° c ./ min to 300 ° c . for 4 hours . these calcined solids are then washed with deionized water ( 20 ml , three times ) and dried in a vacuum oven at 50 ° c . for 18 hours . the washed solids are calcined in a muffle furnace by heating at 10 ° c ./ min to 110 ° c . for 4 hours and then heating at 2 ° c ./ min to 600 ° c . for 4 hours . the solids are transferred to a quartz tube and reduced with a 4 vol . % hydrogen in nitrogen stream at 100 ° c . for 1 hour ( 100 ml / hr ), followed by nitrogen for 1 hour while cooling from 100 ° c . to 23 ° c . to produce comparative catalyst 1a . comparative catalyst 1a contains 0 . 91 wt . % pd . catalyst 1b ( nanopd / nanotio 2 on tio 2 carrier ): an aqueous dispersion ( 16 ml ) containing 3 . 5 wt . % solids of nano - palladium ( 6 nm ) on nano - tio 2 ( 20 nm ) is added by incipient wetness to spray dried titania ( 20 g , 40 micron size , calcined in air at 700 ° c .). the solids are calcined in air by heating at 10 ° c ./ min to 110 ° c . for 4 hours and then at 2 ° c ./ min to 300 ° c . for 4 hours . the calcined solids are transferred to a quartz tube and reduced with a 4 vol . % hydrogen in nitrogen stream at 100 ° c . for 1 hour ( 100 ml / hr ), followed by nitrogen for 1 hour while cooling from 100 ° c . to 23 ° c . to produce catalyst 1b . catalyst 1b contains 0 . 6 wt . % pd . comparative catalyst 2a ( pd — pb / tio 2 ): a solution of 2 . 56 m nitric acid ( 2 . 5 ml ), deionized water ( 5 . 5 ml ), a palladium nitrate solution ( 0 . 53 g , 20 . 64 wt % palladium ) and 0 . 17 wt . % lead nitrate ( 57 . 8 wt % pb ) is added by incipient wetness to spray dried titania ( 10 g , 40 micron size , calcined in air at 700 ° c .). the solids are calcined , washed , re - calcined , and reduced according to the procedure of comparative catalyst 1a to produce comparative catalyst 2a . comparative catalyst 2a contains 0 . 9 wt . % pd and 0 . 8 wt . % pb . catalyst 2b pb / nanopd / nanotio 2 on tio 2 carrier ): lead nitrate ( 0 . 35 g ) is dissolved in deionized water ( 8 ml ) and this solution is mixed with an aqueous dispersion ( 8 ml ) containing 7 . 4 wt . % solids of nano - palladium ( 6 nm ) on nano - tio 2 ( 20 nm ) and the mixture is added by incipient wetness to spray dried titania ( 20 g , 40 micron size , calcined in air at 700 ° c .). the solids are calcined and reduced according to the procedure of example 1b , with the exception that the solids are calcined at 600 ° c . instead of 300 ° c . for 4 hours , to produce catalyst 2b . catalyst 2b contains 0 . 5 wt . % pd and 0 . 74 wt . % pb . catalyst 2c ( nanopd / nanopb / nanotio 2 on tio 2 carrier ): catalyst 2c is prepared according to the procedure of catalyst 1b except that the dispersion used is prepared by simultaneously vaporizing pd and pb powders with tio 2 ( metals = 4 . 7 nanometers ), and the solids are calcined at 600 ° c . instead of 300 ° c . for 4 hours , to produce catalyst 2c . catalyst 2c contains 0 . 9 wt . % pd and 0 . 8 wt . % pb . comparative catalyst 3a ( pd — pb / ts - 1 ): lead nitrate ( 0 . 07 g ) in 16 ml of deionized water is added to 5 ml of 2 . 56 molar nitric acid to form a lead nitrate solution , and an aqueous solution of palladium nitrate ( 0 . 21 g , 20 . 64 wt . % pd ) is added with mixing . the pd — pb solution is then added by incipient wetness to spray dried ts - 1 ( 20 g , 40 micron size , 20 % silica binder , calcined in air at 550 ° c .). the solids are calcined in air by heating at 10 ° c ./ min to 110 ° c . for 4 hours and then at 2 ° c ./ min to 300 ° c . for 4 hours . then the calcined solids are calcined again and reduced according to the procedure of example 2b to produce comparative catalyst 3a . comparative catalyst 3a contains 0 . 27 wt . % pd , 0 . 21 wt . % pb and 1 . 8 wt . % ti . catalyst 3b ( pb / nanopd / nanotio 2 on ts - 1 ): lead nitrate ( 0 . 132 g ) is dissolved in deionized water ( 38 ml ) and this solution is mixed with an aqueous dispersion ( 2 . 7 ml ) containing 7 . 4 wt . % solids of nano - palladium ( 6 nm ) on nano - tio 2 ( 20 nm ) and the mixture is added by incipient wetness to spray dried ts - 1 ( 40 g , 40 micron size , 20 % silica binder , calcined in air at 550 ° c .). the solids are calcined , recalcined and reduced according to the procedure of comparative catalyst 3a . catalyst 3b contains 0 . 18 wt . % pd , 0 . 23 wt . % pb and 1 . 9 wt % ti . comparative catalyst 4a ( pd — pb / ti - mww ): lead nitrate ( 0 . 025 g ) in 13 ml of deionized water ( 13 ml ) is added to 2 ml of 2 . 56 m nitric acid to form a lead nitrate solution , and an aqueous solution of palladium nitrate ( 0 . 08 g , 20 . 64 wt . % pd ) is added with mixing . the pd — pb solution is then added by incipient wetness to spray dried ti - mww ( 8 g , 5 micron size , calcined in air at 530 ° c .). the solids are calcined , recalcined and reduced according to the procedure of comparative catalyst 3a . comparative catalyst 4a contains 0 . 17 wt . % pd , 0 . 14 wt . % pb and 1 . 2 wt . % ti . catalyst 4b ( nanopd / nanopb / nanotio 2 on ti - mww ): an aqueous dispersion ( 14 . 3 ml ) containing 0 . 64 wt . % solids of nano - palladium / nano - lead ( 7 nm , made by vaporizing a pd / pb alloy with tio 2 ) on nano - tio 2 ( 20 nm ) and the mixture is added by incipient wetness to spray dried ti - mww ( 8 g , 5 micron size , calcined in air at 530 ° c .). the solids are calcined , recalcined and reduced according to the procedure of comparative catalyst 3a . catalyst 4b contains 0 . 11 wt . % pd , 0 . 14 wt . % pb and 1 . 5 wt . % ti . epoxidation runs for catalysts 1a - 3b : a 300 - cc stainless steel reactor is charged with catalyst 3a or 3b ( 0 . 7 g ) or a mixture of ts - 1 ( 0 . 63 g , 20 g , 40 micron size , 20 % silica binder , calcined in air at 550 ° c .) and one of catalysts 1a - 2c ( 0 . 07 g ), methanol ( 100 g ) and 13 grams of a buffer ( 0 . 1 m aqueous ammonium phosphate , ph = 6 ). the reactor is then charged to 300 psig of a feed consisting of 4 % hydrogen , 4 % oxygen , 5 % propylene , 0 . 5 % methane and the balance nitrogen ( volume %). the pressure in the reactor is maintained at 300 psig via a back pressure regulator with the feed gases passed continuously through the reactor at 1600 cc / min ( measured at 23 °° c . and one atmosphere pressure ). in order to maintain a constant solvent level in the reactor during the run , the oxygen , nitrogen and propylene feeds are passed through a two - liter stainless steel vessel ( saturator ) preceding the reactor containing 1 . 5 liters of methanol . the reactor is stirred at 1500 rpm . the reaction mixture is heated to 60 ° c . and the gaseous effluent is analyzed by an online gc every hour and the liquid analyzed by offline gc at the end of the 18 hour run . propylene oxide and equivalents (“ poe ”), which include propylene oxide (“ po ”), propylene glycol (“ pg ”), and propylene glycol methyl ethers (“ pm ” s ), are produced during the reaction , in addition to propane formed by the hydrogenation of propylene . epoxidation runs for catalysts 4a and 4b : a 300 cc stainless steel reactor is charged with catalyst 4a or 4b ( 0 . 7 g ), tert - butanol ( 86 g ), deionized water ( 25 g ), and 13 grams of a buffer ( 0 . 1 m aqueous ammonium phosphate , ph = 6 ). the epoxidation is then run according to the procedure for epoxidation runs using catalysts 1a - 3b . propylene oxide and equivalents (“ poe ”), which include propylene oxide (“ po ”), propylene glycol (“ pg ”), and propylene glycol tert - butyl ethers , are produced during the reaction , in addition to propane formed by the hydrogenation of propylene . the epoxidation results ( see table 1 ) show that supported palladium nanoparticles on titanium zeolite ( ts - 1 or ti - mww ) catalysts are more active and more selective than comparable catalysts produced by depositing palladium compounds directly onto the titanium zeolite . the results also show that catalyst mixtures comprising titanium zeolite and supported palladium nanoparticles show increased catalyst activity compared to comparable catalysts produced by depositing palladium compounds onto the carrier .