www.mrsouvenir.co.ccMC LC (?)5 C s ca xc tc d th 15.1 Cc giai on c bn trong xc tc d th 15.2 ng hc v c ch cc phn ng xc tc d th45.2.1 Vai tr ca hp ph trong xc tc d th4Quan h hp ph v ng hc xc tc 6Phng trnh Freudlich 6Phng trnh Langmuir 65.2.2 ng hc v m hnh phn ng 85.2.3 Cc c ch phn ng pha kh105.2.3.1 C ch LangmuirHinshelwood (1921) 105.2.3.2 C ch EleyRideal (1943) 125.3 Cc l thuyt ( tng) v xc tc d th 16 5.3.1 Kha cnh nng lng v quan h vi hot tnh xc tc165.3.2 Vai tr ca yu t khng gian305.3.3 Yu t in t41Xc tc xi ho kh 41Xc tc Axid/Baz (Xc tc ion) 415.3.3.1 Kim loi435.3.3.2 Xc tc lng kim (bimetallic) 485.3.3.3 Xc tc bn dn53Mi quan h gia cu to v tnh cht bn dn 54Pha tp tng dn ca bn dn 55Hp ph ho hc trn bn dn 57Hp ph xi 58Hp ph hyr 58Trng hp TiO258Phn ng trn b mt bn dn58Trng hp xc tc xi ho58Cc dy hot tnh 60Cc v d la chn xc tc:60Phn ng phn hu N2O 60Xt phn ng xi ho CO trn bn dn 61Phn ng phn hu etanol 62Phn ng hyr ho etylen 63iwww.mrsouvenir.co.ccCht mang 645.3.3.4 Cht cch in: Xc tc axit v xc tc baz66Tnh axit b mt 66Xc tc baz rn735.4Tnh cht xc tc trong thc t 795.4.1 Cc yu t nh hng n cc tnh cht xc tc 795.4.2 Xc tc trn cht mang80Vai tr ca cht mang:81Chc nng ca cht mang: 81Cht mang dn ti tnh a chc: 86Hiu ng SMSI 86Phn ng hyr ho axeton thnh isopropanol:865.4.3 Cc cht xc tin885.4.4 Cht c ch 925.5 S mt hot tnh v S ti hot ho945.5.1 S u c xc tc 955.5.2 S u c trong xc tc kim loi 965.5.3 S u c xc tc xit bn dn985.5.4 S u c xc tc axit985.5.5 Cc sn phm phn r (deposit) bm trn b mt xc tc985.5.6 Cc qu trnh nhit v s thiu kt1005.5.7 Tn tht xc tc qua pha kh101M hnh s mt hot tnh 102M hnh da trn hp ph Langmuir 102Ti sinh xc tc 1035.6 Cc c trng xc tc d th 1055.6.1 Xc nh cc c trng vt l v ho l1065.6.2 c trng ho hc v c trng b mt 111Phng php phn ng theo chng trnh nhit 112Hin vi in t truyn qua (TEM) 113Nhiu x in t nng lng thp(Low-Energy Electron Diffraction(LEED)) 114Ph hng ngoi (IR)114Ph in t phn tch ho hc (Elec/ Spectr. for Chem. Analysis= ESCA) 115Ph in t Auger - Auger Electron Spectroscopy (AES) 116Ph bn ph ion - Ion Scattering Spectroscopy (ISS) 117iiwww.mrsouvenir.co.ccKhi ph ion th cp (Secondary Ion Mass Spectrometry = SIMS) 117Ti liu sch gio khoa v xc tc d th v ho l b mt122iiiwww.mrsouvenir.co.ccDANH MC BNGBng 5-1 So snh cc bc trong phn ng ng th v d th 3Bng 5.2 So snh hp ph vt l v hp ph ho hc 5Bng 5-3 Mt s v d hp ph ho hc 5Bng 5.4 Phn loi kim loi theo kh nng hp ph ho hc17Bng 5-5 Hp ph ho hc CO trn kim loi chuyn tip22Bng 5.6 Ph IR ca CO hp ph trn cc xc tc Ni trn cht mang 23Bng 5-7 Cc vng hp th IR ca phc etylen 23Bng 5-8 So snh hot tnh xc tc kim loi chuyn tip trong mt s phn ng25Bng 5-9 Cu trc v khong cch mng kim loi (khong cch ti nguyn t bn cnh gn nht o bng nm)31Bng 5-10 Phn loi cc phn ng xc tc bi kim loi34Bng 5-11 Hiu ng khng gian trong mt s phn ng 34Bng 5-12 Hp ph v hyr ho etylen trn cc b mt niken35Bng 5-13 Hot tnh cc mt tinh th Fe khc nhau trong phn ng tng hp NH336Bng 5-14 Phn loi xc tc rn 42Bng 5-15 Hot tnh xc tc so snh ca cc kim loi 48Bng 5-16. Cc xc tc lng kim v cc qu trnh cng nghip tng ng 48Bng 5-17 Hyr ho etylaxetat etanol trn xc tc Rh/Sn-SiO249Bng 5-18 Hyr ho crotonalehit trn xc tc Pt49Bng 5-19 Hyr ho dn xut ca pyridin vi xc tc lng kim mang trn Al2O3 51Bng 5-20 Bin tnh xc tc nhm Pt bng kim loi th hai51Bng 5-21 Nng lng kch thch bt in t ca mt s vt liu 53Bng 5.22 Tnh cht ca mt s xit bn dn 55Bng 5.23 Phn loi cc xit kim loi theo tnh cht in t56Bng 5.24 xi ho CO trn xc tc bn dn62Bng 5-25 Phn hu etanol trn xc tc xit bn dn 63Bng 5-26 Phn ng trn xc tc trn cht mang 64Bng 5.27 Phn loi xc tc A/B d th62Bng 5.28 Hiu qu ca Al2O3 vi axit khc nhau trong phn ng loi nc etanol 71Bng 5.29 axit ca cc vt liu xit hn hp72Bng 5.30 Xc tc axit trong mt s phn ng (xp theo s tng axit)73Bng 5.31 Cc cht mang xc tc cng nghip, tnh cht v ng dng 80Bng 5-32 La chn cht mang xc tc81Bng 5.33 Hyr phn trn xc tc Ni trn cc cht mang khc nhau (10% Ni)83Bng 5.34 ehyr ho xyclohexan thnh benzen trn xt Pt/cht mang 773K84Bng 5.35 Hy ho CO trn xc tc Pd vi cc cht mang khc nhau 84Bng 5.36 Hot tnh tng i ca Rh trn cc xit trong phn ng hyr hoCO84iwww.mrsouvenir.co.ccBng 5.37 nh hng ca cht mang n sn phm hyr ho CO trn Rh 85Bng 5.38 Xc tc Cu trn cc loi xit trong phn ng hyr ho CO85Bng 5.39 Hiu ng SMSI trong phn ng hyr ho axeton thnh isopropanol trn xc tc Pt vi cc cht mang khc nhau 87Bng 5.40 Cc v d v cc cht xc tin trong xc tc cng nghip ` 89Bng 5-41 Nguyn nhn mt hot tnh ca mt s xc tc cng nghipBng 5-42 Cc cht c v c ch xc tc96Bng 5-43 Chuyn ho nafta trn xc tc 0,6%Pt /Al2O3, s mt hot tnh v ti sinh 101Bng 5-44 Din tch b mt ring ca mt s xc tc v vt liu mang 110Bng 5-45 Hp ph ho hc c trng b mt kim loi111iiwww.mrsouvenir.co.ccDANH MC HNHHnh 5-1 Cc bc c bn trong phn ng xc tc d th vi xc tc rn xp 1Hnh 5-2 Din bin nng theo v tr trong trng hp phn ng xy ra trong vng khuch tn ngoi (a), khuch tn trong l (b), v ng hc 2Hnh. 5-3 S ph thuc ln tc thc t, reff vo i lng nhit nghch 3Hnh 5-4 ng hp ph ng nhit (isotherm) Langmuir6Hnh 5-5 S c ch LangmuirHinshelwood 10 Hnh 5-6 Cc trng hp ca phn ng lng phn t pha kh theo c ch L-H 11Hnh 5-7 C ch EleyRideal 12Hnh 5-8. S ph thuc tc phn ng vo nng cht A trong phn ng pha kh lng phn t theo c ch EleyRideal 13Hnh. 5-9 Din bin ca phn ng pha kh Ag Pg16Hnh 5-10 Hp ph ho hc hay s hnh thnh phc etylen - b mt Pt19Hnh 5-11 S thay i th nng ca h H2 hp ph trn Ni 19Hnh 5-12 C ch hp ph phn li ca H2 trn b mt Ni 20Hnh 5.13 Quan h hot tnh so snh ca cc kim loi trong phn ng phn hu axit foocmic vi nhit hnh thnh foocmat kim loi24Hnh 5.14 Quan h hot tnh v nhit hp ph trong tng hp amnic 24Hnh 5.15 Quan h gia entalpy hp ph ho hc trung bnh ca hyr v v tr ca nguyn t trong bng tun hon26Hnh 5.16 Cc mt phng tinh th trong mng lp phng v ch s Miller tng ng31Hnh 5-17 S cc nguyn t xung quanh v ho tr t do ca cc nguyn t b mt Ni ng vi cu trc fcc 32Hnh 5.18 M hnh b mt tinh th (BASF, Ludwigshafen, Germany) 33Hnh 5.19 Quan h tc phn ng v khong cch kim loikim loi trong xc tc hyr ho etylen 35Hnh 5.20 Phn ng xi ho CO trn b mt Pt 37Hnh 5-21 Hp ph v phn hu axetonitril trn b mt Ni 38Hnh 5-22 Qu trnh truyn in t 42Hnh 5-23 Mt in t 3d v cng thot o ca cc kim loi chu k 4 43Hnh 5-24 Thuyt vng: s thay i mc Fermi khi hp ph: 44Hnh 5-25 Hot tnh xc tc trong phn ng CO + H2 CH4 trn cc kim loi44Hnh 5-26 Quan h hot tnh xc tc trong phn ng hyr ho etylen v c trng d 45Hnh 5-27 Quan h i lng hp ph hyr trn xc tc hp kim CuNi v thnh phn46Hnh 5-28. Hot tnh ring ca hp kim CuNi trong phn ng ehyr ho xyclohexan v hyr phn etan thnh metan 316oC 47Hnh 5-29 Bn dn thc v hin tng kch thch to in tch 53Hnh 5-30 Bn dn v hot ng ca chng theo kiu: 54Hnh 5-31 Hot tnh so snh ca cc xit trong phn ng phn hu N2O 61Hnh 5.32 Cc tm axit trn b mt xit nhm Al2O367iwww.mrsouvenir.co.ccHnh 5-33 C ch phn ng ehyrat ho etanol trn nhm oxit 71Hnh 5-34 Cc tnh cht quan trng nht ca xc tc cng nghip 79Hnh 5.35 M hnh hyr ho axeton trn Pt/TiO2 v hiu ng SMSI87Hnh 5-36 S tc ng ca K trong hp ph phn li N2 trn xc tc Fe 90Hnh 5-37Cc kiu gim hot tnh 95Hnh 5-38 Cc c ch lm gim hot tnh xc tc (M = kim loi) 95Hnh 5-39 S cc ho qua con ng ehyr ho 99Hnh 5-40 S mt hot tnh trong cc qu trnh chuyn ho (reforming) xc tc99Hnh 5-41 Din bin hot tnh trong qu trnh phn ng, trc v sau ti sinh 103Hnh 5-42 S cc phng php nghin cu xc tc 106Hnh 5-43 ng ng nhit hp ph vt l ??????Hnh 5-44 My o hp ph (Phng th nghim Xc tc, FH Mannheim, c) 111Hnh 5-45 Ph TPD ca amoniac gii hp t zeolit112Hnh 5-46 Nguyn l thit b gii hp ph theo chng trnh nhit (temperature programmed reduction TPR)112nh AMI 114Hnh 5-47 Tp hp cc tinh th platin trong xc tc Pt/graphit: nh lng bng ph XPS (hnh gia hng trn), hnh nh TEM (hng di) (BASF, Ludwigshafen, c) 114Hnh 5-48 My ph ESCA (BASF, Ludwigshafen, c) 116Hnh 5-49 Ph ESCA ca xc tc Ag/Al2O3116Hnh 5-50 Ph ISS ca xc tc bc trc v sau s dng trong phn ng xi ho etylen 117Hnh 5-46 So snh khoa hc b mt vi xc tc cng nghip 119????iiwww.mrsouvenir.co.ccDANH MC CC S S 5.1 C ch hyr ho alken26S 5.2 C ch hyr ho chn lc axetylen27S 5.3 C ch phn ng xi ho 59S 5.4 Hyr ho etylen trn xc tc ZnO 63S 5.5 Phn ng reforming n-hexan trn xc tc Pt/Al2O386S 5.6 Phn ng reforming metan vi CO2 trn xc tc Rh/Al2O388iwww.mrsouvenir.co.cc5 C s ca xc tc d th5.1 Cc giai on c bn trong xc tc d thBn thn phn ng xc tc d th l kt qu ca nhiu qu trnh l hc cng nh ho hc k tip nhau. Trong nhiu ti liu ngi ta gi y l c ch v mca phn ng xc tc d th.C ch ny bao gm 7 bc k tip nhau. Xt phn ng pha kh A + XT P + XT, ta c cc bc: (1) phn t cht phn ng A khuch tn t th tch phn ng (kh, lng), qua lp mng kh st b mt xc tc rn ti l xp; (2) A khuch tn trong l ti tm hot ng trn b mt xc tc (rn); (3) A hp ph trn tm hot ng; (4) A thc hin phn ng chuyn ho thnh sn phm P; (5) P gii hp khi b mt xc tc v (6) P thc hin qu trnh khuch tn ngc ra khi l v (7) P ra khi l mng kh b mt, ngc vi A bc (1), gii phng b mt cho chu trnh chuyn ho tip theo. Trong trng hp xc tc c h l xp rt nh, khi cc phn t A hoc P khng th chuyn ng t do nh trong pha kh, chng gn nh phi b trong khe hp khi thc hin qu trnh xc tc. Khi bc (2) v (6) ng vai tr rt quan trng, phn bit hai qu trnh khuch tn i khi ngi ta gi l l khuch tn ngoi v khuch tn trong (l) [T20, T26]. Cc qu trnh va nu c m t trn hnh 5.1. Khi xem xt ng hc phn ng xc tc d th ta phi lu n quy tc: giai on chm nht l giai on quyt nh vn tc ton b qu trnh. Hnh 5-1 Cc bc c bn trong phn ng xc tc d th vi xc tc rn xpTrong xc tc d th bn thn phn ng ho hc (bc 4) l quan trng nhng giai on hp ph (bc 3, 5) cng rt quan trng v khng th tch ri khi (4). Trong trng hp vn tc bn thn phn ng ho hc chm hn, giai quyt nh vn tc l bc (4), khi ta ni phn ng xy ra trong vng ng hc, ng hc khi l ng hc vi m. Trng hp ngc li, khi vn tc phn ng ln, vn tc khuch tn vn chuyn cht nh ta ni phn ng xy ra trong vng khuych tn, ng hc trong trng hp ny l ng hc v1www.mrsouvenir.co.ccm. Nh vy, phng trnh ng hc ca ton b qu trnh s th hin tc ca qu trnh chm nht. Cc yu t nh hng n tc thc t ca phn ng, reff, c nhiu, l bn cht b mt phn cch pha, xp v cu trc h l xp, tc chuyn khi trn lp b mt, v tt nhin l bn cht xc tc. Nu phn ng xy ra trong vng khuch tn th cc s liu ng hc s th hin quy lut ca qu trnh chuyn khi vt l, khi ta khng thu c thng tin chnh xc v bn thn phn ng ho hc. Nh vy, nu ta mun nh gi ng c ch phn ng th cn m bo rng phn ng trong iu kin nghin cu phi xy ra vng ng hc.Vd,ta cth loi b yu tkhuch tn mng bng cch tng tc dng kh.Nu khuch tn trong l xp chm, ta c th gim kch thc ht xc tc gim ng i ca phn t cht phn ng, iu ny phi c thc hin cho ti khi yu t khuch tn trong ht nh hng. thy r cc iu nu, ta xem xt gin nng cht phn ng - v tr xc nh nng theo chiu i vo tm ht xc tc (hnh 5.2). Hnh 5-2 Din bin nng theo v tr trong trng hp phn ng xy ra trong vng khuch tn ngoi (a), khuch tn trong l (b), v ng hcTheo hnh 5.2 ta c cc trng hp sau:a) Khuch tn ngoi (trn lp mng tip xc kh/rn) hoc khuch tn trong l xp l giai on quyt nh: y l trng hp tc phn ng ho hc rt nhanh so vi khuch tn; cht khuych tn vo bao nhiu s chuyn ho ht by nhiu.b) Khuch tn trong l giai on quyt nh: tc phn ng nhanh hn so vi khuch tn trong l nhng chm hn so vi khuch tn ngoi; cht khuch tn vo ti tm hot ng bao nhiu s chuyn ho ht by nhiu, tc s th hin tc khuch tn trong.c) Vng ng hc: tc phn ng chm so vi c hai dng khuch tn.Khi thay i nhit phn ng tc phn ng thay i theo quy lut nh (H. 5-3). 2www.mrsouvenir.co.ccHnh. 5-3 S ph thuc ln tc thc t, reff vo i lng nhit nghchTrong vng ng hc tc phn ng tng nhanh khi nhit tng, nng lng hot ho xc nh theo Arrhenius s l nng lng hot ho ca bn thn phn ng, tng t nh trng hp phn ng ng th. Trong vng khuych tn trong, tc qu trnh cng tng theo nhit v tun theo phng trnh Arrhenius, tuy nhin dc s thp hn, khi phn xc tc thc s hot tnh s gim. Khi tng nhit vn tc qu trnh s tng nhng tngchm hn vngnghcTrongvng khuych tn ngoi (cn gil khuych tn mng) tc , reff, tng khi tng nhit phn ng nhng s tng chm hn na. Tng ng nng lng hot ho trong min ng hc cao nht v nng lng hot ho trong vng khuych tn ngoi s thp nht tnh theo phng trnh Arrhenius.Trong thc t, cc phng trnh ton hc ca ton b qu trnh xc tc d th s kh phc tp v ng thi phi tnh ti c cc qu trnh vt l (khuych tn) v cc qu trnh ho hc (hp ph-chuyn ho), ngoi ra cn tnh ti c nhit phn ng v cc qu trnh truyn nhit. Trong nhiu trng hp do m hnh ton hc rt phc tp v phi gii bng cc phng php s. Cc phn ng ng th v d th c bn thng gp c nu v so snh trong Bng 5-1. Ta thy s c mt s iu tng ng.Bng 5-1 So snh cc bc trong phn ng ng th v d thng th D th-Hnhthnhccv tr trngtrongkhnggian phcTo phc vi cc phn t nh nh H2, COPhn ng cng-xi ho, hnh thnh lin ktPhn ng cngv chuyn hovng meta;cc tng tc i nhn hoc i in tPhn ng tch-kh, loi tr ( -elimination)Khuych tn cht phn ng ti tm b mt xc tc rnHp ph vt lHp ph ho hcPhn ng chuyn ho trn b mtQu trnh gii hp, khuych tn ngc3www.mrsouvenir.co.cc5.2 ng hc v c ch cc phn ng xc tc d th [T20, T32]Hiu bit v ng hc rt quan trng trong xc tc d th v nhng l do sau:1) Khi c phng trnh ng hc ngha l bit bc phn ng i vi tng cht phn ng hay sn phm ta s tm c c ch phn ng. Khi c c ch phn ng ta c c s khoa hc ti u ho xc tc, iu m hin nay ch yu c lm bng thc nghim rt tn km.2) Bn thn cc thng s bn phn ng, cc thng s hnh hc, cu trc ca ht xc tc c lin h cht ch vi bc phn ng v cc thng s nhit ng ca phn ng.3) Khi kho st s ph thuc ca tc phn ng vo nhit s thu c nng lng hot ho, gi tr ca i lng ny l bng chng v giai on no s quyt nh vn tc ton b qu trnh phn ng.Nh bit, qu trnh hp ph v cc thng s hp ph l thnh phn khng tch ri ca ng hc phn ng xc tc d th, v vy tip theo ta s xem xt yu t hp ph trong ng hc ca cc phn ng trn xc tc d th. 5.2.1 Vai tr ca hp ph trong xc tc d th [T42, T43]Trc ht cn phn bit hai qu trnh hp ph vt l v hp ph ho hc.Hp ph vt l l h qu tng tc gia cc phn t trn b mt cht rn vi cc phn t trong pha kh hoc lng nh cc lc van der Waals, khi lng nhitto ra trong qu trnh hp ph xp x gi tr i lng nhit ho hi ca cht b hp ph.Trong hp ph ho hc s hnh thnh lin kt gia cc phn t cht b hp ph v cc nguyn t b mt xc tc. trng thi b hp ph cc phn t cht phn ng tr nn hot ng hn, nhit hp ph trong trng hp ny xp x nhit phn ng ho hc. V d: nhit hp ph ca xi trn carbon l xp x 330 kJ/mol, ngha l xp x nhit ca phn ng t chy carbon (394 kJ/mol).iu ny khng c ngha l cht hp ph mnh s l xc tc tt. Trong thc t, mc d khng c hp ph th khng c xc tc nhng khng phi cht hp ph no cng s l cht xc tc, l v phn ng xc tc mang tnh c th, trong khi hp ph th khng. Nh vy c th ni hp ph l iu kin cn nhng cha . iu th hai cn lu l phi phn bit r kh nng hp ph (tc l 1 gam hoc 1 m2 cht rn s hp ph c bao nhiu phn t cht b hp ph) v tc (ng hc) hp ph.Chaidng hp phu to nhit, v vy khi nhit tng cn bng hp ph s dch chuyn v pha gii phng cht b hp ph. Hp ph vt l l qu trnh rt nhanh, cn bng s thit lp nhanh ngay c nhit thp. Hp ph ho hc, tng t nh phn ng ho hc, thng c nng lng hot ho cao, tc hp ph s tng khi nhit tng.V kha cnh p sut, tc c hai dng hp ph tng ng bin vi p sut. Hp ph ho hc ch xy ra i vi cc phn t cht b hp ph lp st b mt rn (hp ph n lp), 4www.mrsouvenir.co.ccngc li hp ph vt l c th dn n hp ph a lp. Bng 5.2 tng hp cc so snh hai dng hp ph ny. Bng 5.2 So snh hp ph vt l v hp ph ho hcHp ph vt l Hp ph ho hcNguyn nhn lc van der Waalskhng c trao i in tlin kt ng ho tr/lc culonc trao i in tCht hp ph tt c cht rn mt s cht rnCht b hp ph tt c kh nhit < nhit ti hn, phn t khng thay imt s kh c kh nng phn ng, phn li thnh nguyn t, ion, gc t doKhong nhit thp thng caoNhit hp ph nh, xp x nhit nng chy (~ 10 kJ/mol), lun dngln, xp x nhit phn ng (~ 80-200 kJ/mol), thng dngTc rt cao rt ph thuc nhit Nng lng hot ho thp thng cao (tr khi khng cn hot ho)Lp ph b mt a lp n lpMc thun nghch rt cao thng thun nghchng dng o din tch b mt, kch thc l xpo nng b mt v ng hc, o tc hp ph v gii hp, xc nh bn cht tm hot ngBn cht b mt nh hng mnh m n hp ph. Trong hp ph vt l s nguyn t b mt ni chung l quan trng nhng trong hp ph ho hc bn cht b mt mi l quan trng. V d, hyr hp ph ho hc trn niken nhng khng hp ph trn xit nhm, xi hp ph trn carbon nhng khng hp ph trn MgO. Mt s v d hp ph ho hc c nu trong bng 5-3.Bng 5-3 Mt s v d hp ph ho hcH Nhit hp ph, kJ/mol Nng lng hot ho, kJ/molH2 trn graphitCO trn Cr2O3N2 trn Fe (xc tin Al2O3, K2O)CO trn PdH2 trn W18938 6314772 7684 - 315250,8 3679,6 38,042 105Hnh dng b mt, cu trc b mt cng quan trng trong hp ph ho hc. V d, nhng phn b mt g gh (gc, cnh) v cc khuyt tt b mt s ng vai tr quan trng. c bit, nhng phn tri ln thng cha cc nguyn t c cc ho tr d thng ng vai tr cc tm hot ng. V d trong phn ng cracking cumene, nng tm hot ng tnh c l 3,6*1019/g xc tc hoc 1,2*1017/m2 b mt xc tc.Tng kt li, cc yu t sau s nh hng mnh ti ng hc xc tc:1) Hp ph l bc i trc bn thn phn ng xc tc d th (XTDT).5www.mrsouvenir.co.cc2) Phn ng XTDT bao gm hp ph ho hc, y l qu trnh c trng v l phn ng gia phn t cht phn ng v b mt xc tc.3) B mt xc tc khng ng nht, ch mt phn nh cc nguyn t b mt l tham gia phn ng, y lcc tm hot ng.Sau y ta s xem xt cc quy lut hp ph v vai tr ca hp ph trong ng hc xc tc [15,T32].Quan h hp ph v ng hc xc tcPhng trnh FreudlichThng cn bng hp ph c biu din bng cc phng trnh kinh nghim. Phng trnh Freundlich (Pt. 5-1) l mt dng thng gp.nA F Ap a C (5.1)CA = nng cht b hp ph A trn b mtpA = p sut ring phn ca A trong iu kin cn bngaF = h s thc nghim, c trng cho h hp ph-b hp ph nhn = l s nm gia 0 v 1Phng trnh LangmuirQuan h gia CA v pA cng c m t bng phng trnh vi hai hng s l phng trnh Langmuir (Pt. 5-2).AAAbpbpC C+1(5.2)C = hp ph cc i b = hng s cn bng hp ph = kad/kdeadng biu din quan h CA pA nhit constant c dng nh (H. 5-4): CA tng dn v tim cn Cng vi hp ph n lp (mononuclear coverage) trn b mt. ng cong trong H. 5-4 c gi l ng hp ph ng nhit hay iosotherm.H. 5-4 ng hp ph ng nhit (isotherm) Langmuir Dung lng hp ph n lpchephbmtmaxDung lng hp ph n lpchephbmtmax6www.mrsouvenir.co.ccKhi b hoc pA ln pt. chuyn thnh dng CA = C, ngha l hp ph t gi tr n lp, ffy l trng hp phng trnh Freundlich c n = 0. Khi pA hoc b c gi tr rt nh phng trnh 5-2 c dng nh phng trnh Freundlich vi n = 1 (Pt. 5-3).A Abp C C(5.3) cc gi tr b hoc pA trung gian ta c trng hp ca phng trnh Freundlich vi n= 01.p dng phng trnh Langmuir cho trng hp hp ph ho hc vi gi thit l b mt ng nht v mt nng lng, khi entalpy hp ph s khng ph thuc vo mc che ph b mt bi phn t cht A k hiu l A.Xt phn ng gia A pha kh vi b mt F pha rn ta c:A(g)+F(s)AF(s) (5.4)Khi ta vit c cn bng:A FAFAp CCK (5.5)CAF = nng A trn cc tm hot ng b mt trn mt n v b mtCF = nng cc tm hot ng trn mt n v b mtKhi (1 A) l phn b mt t do, ta c:CAF = A CF = (1 A)Nh vy Pt.5-5 chuyn thnh Pt.5-6:( )A AAApK1(5.6)T y tm c biu thc ca A (Pt.5-7):A AA AAp Kp K+1(5.7)Tip theo ta xy dng quan h gia cc i lng hp ph vi phng trnh tc phn ng xc tc d th nh sau.Xt phn ng n gin A C vi gi thit l A hp ph v khng phn licn C khng hp ph. Khi tc chuyn ho A ch ph thuc vo phn A b hp ph, ta c: A AA AAAp Kp kKkdtdp+ 1(5.8)Xt cc trng hp sau:7www.mrsouvenir.co.cc1) Nu KA hoc pA rt nh, khi KApA > 1, ta c dpA/dt = k ngha l A = 1, hp ph l cc i v tc phn ng khng ph thuc vo pA, phn ng l bc zero theo A. Nu hai iu kin bin u khng ph hp, khi bc phn ng theo A phi c gi tr gia 0 v 1. Nu c th theo di c phn ng vng p sut (nng ) rng, khi ta s thy khi p sut gim dn th bc phn ng s tin ti mt v khi p sut tng dn bc phn ng s gim dn ti khng.3) Trng hp thng gp hn l trng hp c hai cht phn nghay hp ph hn hp. Ta xt trng hp ny vi gi thit hai kh A v B s cnh tranh chim ch cc tm t do, khi phn b mt t do s bng (1 A B), khi ta c phng trnh 5-9 v 5-10 biu din mc che ph b mt bi mi tc nhn phn ng: B B A AA AAp K p Kp K+ +1(5.9)B B A AB BBp K p Kp K+ +1(5.10)4) Mt s cht hp ph phn li, v d qu trnh sau: (AA)(g)+F(s)AF(s) (5.11)Khi ta c biu thc tng ng:A AA AAp Kp K+1(5.12)Cc qu trnh khc cng xem xt tng t, cc biu thc dn ra y c s dng khi thit lp phng trnh tc phn ng xc tc d th ng thi l c s d bo c ch phn ng [2].5.2.2 ng hc v m hnh phn ng [8, T26] thit k c thit b phn ng cn xy ng c phng trnh tc ,r, v s ph thuc ca tc vo cc thng s lin quan n phn ng. lm r iu ny cn phn bit ng hc vi m v ng hc v m. Khi xem xt mi quan h tc ca bn thn phn ng ho hc v nng cc cht tham gia, nhit , xc tc ta c ng hc vi m. Nu xem xt s ph thuc tc chung ca qu trnh vo cc yu t cng ngh nh chuyn khi v truyn nhit ta c ng hc v m.Theo phng trnh tc 1-2, tc phn ng ph thuc vo nng ca cc cht phn ng v c nng xc tc. Nh bit, phng trnh tc ch mang tnh hnh thc, ch da vo phng trnh ny ta vn cha r c ch phn ng. hiu c ch cn phn bit r phn t s (s ht tham gia vo phn ng c bn) v bc phn ng. .8www.mrsouvenir.co.ccTa cng nhn thy nhiu trng hp m ta khng th gn cho bc phn ng (s m ca nng trong phng trnh tc ) mt gi tr c th. iu ny thng gp trong phn ng xc tc d th. Trong xc tc d th tc phn ng chuyn ho A c th c tnh cho mt n v b mt ring S ca xc tc (m2/(g) hoc kg) thay v chia cho th tch nh phn ng ng th nh Pt.1-2 (Pt.5-13).( )1 2,* * * ,1 s m kg kmol C kfdtdnSrAAS A(5.13)Thng dng hn l dng khi nim tc phn ng c gy ra bi mt g (kg) xc tc, khi ta phi chia tc chuyn ho cho khi lng xc tc, mcat v thu c reff - tc phn ng thc (Pt.5-14):( )1 1,* * ,1 s kg kmol C kfdtdnmrAAcateff A(5.14)Cn lu , tc phn ng thc trong xc tc d th ngoi vic ph thuc vo nng cht phn ng, nhit phn ng nh phn ng ng th cn ph thuc vo cc thng s ng hc v m nh b mt phn cch pha, c ht, t khi, xp, cu trc h l xp v tc khuych tn.Ta s thit lp biu thc tc cho phn ng xc tc d th pha kh sau [T20, T26]: A + B CTrc ht vit cc phng trnh tc cho tt c cc thnh phn c mt (lu : trong phn ng ng th khng c cu t C):cCbBaAp p kp r (5.15) y r l tc tnh cho mt n v khi lng xc tc v k l hng s vn tc c th nguyn ph thuc vo bc phn ng a, b, v c. Thng thng cc s m ny khc mt. S xut hin ca pCl do sn phm c th chim ch trn xc tc do cha kp gii hp ph hoc gii hp ph km.M hnh hnh thc ny thng khng tnh n s thay i ca cc s m (bc phn ng) khi thay i nhit , p sut, v vy ch c ngha trong khong hp nhit v p sut. V vy ngha thc t l khng ln. c m hnh tt hn ta cn xt n yu t hp ph, gii hp ph v s tham gia ca cc thnh phn phn ng. Khi phng trnh tc phi cha p sut ring phn ca mi thnh phn trong hn hp phn ng. Khi phng trnh tc cha ba yu t: (1) yu t ng hc (kinetic term) cha cc i lng nng (p sut ring phn); (ii) yu t ng lc thc y qu trnh (driving force) hay l khong cch n cn bng; (iii) yu t cn tr (resistance term) (Pt.5-16):9www.mrsouvenir.co.cc( ) ( )( )ne f fte r m c e r e s i sfo r c e d r i v i n g t e r m k i n e t i cr_ ta n_ _(5.16)S m (bc) n thng c gi tr 1 hoc 2 v ph thuc vo s tm hot ng tham gia phn ng giai on quyt nh vn tc. Yu t cn tr (resistance term) thng l cc yu t lin quan n hp ph ho hc.Cc yu t trong Pt.5-16 cha cc thng tin v hp ph i vi cc thnh phn phn ng. xy dng phng trnh tc y cn xc nh mi quan h gia vn tc vi nng , nhit , p sut, v cn bit c ch. Trong phn ln cc trng hp n gin ho ngi ta kim sot giai on chm nht giai on quyt nh vn tc l [2]. Khi , phng trnh tc cha cc yu t quyt nh vn tc quan trng nht. i vi phn ng bt thun nghch, khi yu t chuyn khi quyt nh ta thng gp dng Pt.5-17:nA effkp r (5.17)hoc vi phn ng A + B R + S ta s c:( )nR R A AB Aeffp K p Kp kpr+ +1(5.18)Cc phng trnh tc kiu Pt.5-17 v 5-18 c xy dng trn c s l thuyt v tm hot ng. c phng trnh chi tit hn, m t c c c ch phn ng s tn nhiu chi ph v cng sc, trong thc t sn xut ngi ta ch cn nhng thng tin phc v cng tc thit k bn phn ng.5.2.3 Cc c ch phn ng pha kh [15, 34, T35]Trong phn ny ta xem xt phn ng xc tc lng phn t pha kh. Phn ng c dng:AG + BG CG(5-19)C hai c ch. Ta xem xt ln lt.5.2.3.1 C ch LangmuirHinshelwood (1921)Trn c s gi thit l hai cht phn ng A, B hp ph ng thi nhng trn hai loi tm khc nhau, to hai trng thi trung gian b mt khng phn li, tip theo phn ng gia hai cht trung gian to sn phm, sau l gii hp ph sn phm C. Ta c s Hnh 5-5:AG + * A* vBG + * B*A* + B*C* + *C* C + *C khuch tn vo th tch, giiphng tm hot ng *10www.mrsouvenir.co.cc Hnh 5-5 S c ch LangmuirHinshelwoodNh vy, y l qu trnh nhiu bc v bc no cng c th l giai on quyt nh vn tc, tuy nhin thng giai on phn ng ho hc gia hai cht trung gian l giai on chm nht. Nh vy tc phn ng, trng hp hai cht cng hp ph ho hc trn hai loi tm khc nhau,c xc nh theo phng trnh sau:( )21B B A AB B A AB AAeffp K p Kp K p kKkdtdpr+ + (5.20)Cc iu kin bin ca biu thc ny l: 1) Trng hp c hai cht phn ng u hp ph yu, khi c KA v KB