\u0158\u00edzen\u00ed emis\u00ed z automobil\u016f p\u0159edstavuje kl\u00ed\u010dov\u00fd pr\u016fnik environment\u00e1ln\u00ed v\u011bdy, chemick\u00e9ho in\u017een\u00fdrstv\u00ed a ve\u0159ejn\u00e9ho zdrav\u00ed. Srdcem modern\u00edch syst\u00e9m\u016f sni\u017eov\u00e1n\u00ed emis\u00ed z vozidel je katalyz\u00e1tor, za\u0159\u00edzen\u00ed navr\u017een\u00e9 tak, aby p\u0159em\u011b\u0148ovalo \u0161kodliv\u00e9 zne\u010di\u0161\u0165uj\u00edc\u00ed l\u00e1tky vznikaj\u00edc\u00ed p\u0159i vnit\u0159n\u00edm spalov\u00e1n\u00ed na m\u00e9n\u011b \u0161kodliv\u00e9 l\u00e1tky. Po\u010d\u00e1tky t\u00e9to technologie lze vysledovat a\u017e k rostouc\u00edmu pov\u011bdom\u00ed ve\u0159ejnosti o zne\u010di\u0161t\u011bn\u00ed ovzdu\u0161\u00ed, zejm\u00e9na fotochemick\u00e9m smogu a n\u00edzko\u00farov\u0148ov\u00e9mu ozonu, kter\u00e9 se ve 40. letech 20. stolet\u00ed v d\u016fsledku prudk\u00e9ho n\u00e1r\u016fstu pou\u017e\u00edv\u00e1n\u00ed automobil\u016f ve velk\u00fdch m\u011bstech st\u00e1le v\u00edce roz\u0161\u00ed\u0159ilo. 1<\/a>.<\/p>\n\n\n\n Ran\u00e9 v\u00fdzkumn\u00e9 iniciativy v 60. letech 20. stolet\u00ed, podn\u00edcen\u00e9 t\u011bmito environment\u00e1ln\u00edmi obavami, hledaly \u0159e\u0161en\u00ed pro zm\u00edrn\u011bn\u00ed rostouc\u00edch hladin oxidu uhelnat\u00e9ho (CO), uhlovod\u00edk\u016f (HC) a oxid\u016f dus\u00edku (NOx) emitovan\u00fdch vozidly. 3<\/a>Kl\u00ed\u010dovou postavou v tomto ran\u00e9m v\u00fdvoji byl francouzsk\u00fd in\u017een\u00fdr Eugene Houdry, kter\u00fd v letech 1952 a 1973 vyvinul prvn\u00ed praktick\u00e9 katalyz\u00e1tory pro automobily. 4<\/a>Jeho pr\u016fkopnick\u00e1 pr\u00e1ce polo\u017eila z\u00e1klady pro pou\u017eit\u00ed katalyz\u00e1tor\u016f k p\u0159em\u011bn\u011b zne\u010di\u0161\u0165uj\u00edc\u00edch l\u00e1tek na m\u00e9n\u011b \u0161kodliv\u00e9 slou\u010deniny, p\u0159i\u010dem\u017e se zpo\u010d\u00e1tku zam\u011b\u0159oval na aplikace v kom\u00ednech a skladov\u00fdch vysokozdvi\u017en\u00fdch voz\u00edkech p\u0159ed integrac\u00ed do automobilov\u00e9ho pr\u016fmyslu. 4<\/a>.<\/p>\n\n\n\n Oblast kontroly emis\u00ed z automobil\u016f byla z\u00e1sadn\u011b prom\u011bn\u011bna legislativn\u00edmi opat\u0159en\u00edmi, zejm\u00e9na americk\u00fdm z\u00e1konem o \u010dist\u00e9m ovzdu\u0161\u00ed z roku 1970. Tato p\u0159elomov\u00e1 legislativa stanovila p\u0159\u00edsn\u00e9 emisn\u00ed normy a po\u017eadovala 90% sn\u00ed\u017een\u00ed emis\u00ed vozidel do p\u011bti let, \u010d\u00edm\u017e donutila v\u00fdrobce automobil\u016f zav\u00e9st pokro\u010dil\u00e9 technologie kontroly. 1<\/a>Do roku 1975 z\u00e1kon o \u010dist\u00e9m ovzdu\u0161\u00ed na\u0159\u00eddil instalaci katalyz\u00e1tor\u016f do v\u0161ech nov\u00fdch automobil\u016f prod\u00e1van\u00fdch v USA, co\u017e znamenalo v\u00fdznamn\u00fd zlom v regulaci \u017eivotn\u00edho prost\u0159ed\u00ed a automobilov\u00e9m designu. 1<\/a>.<\/p>\n\n\n\n Zpo\u010d\u00e1tku byly zaveden\u00e9 katalyz\u00e1tory \u201edvoucestn\u00e9\u201c oxida\u010dn\u00ed konvertory. Tyto ran\u00e9 konstrukce byly schopny odstra\u0148ovat oxid uhelnat\u00fd a nesp\u00e1len\u00e9 uhlovod\u00edky, ale m\u011bly inherentn\u00ed omezen\u00ed ve sv\u00e9 schopnosti zm\u00edr\u0148ovat emise oxid\u016f dus\u00edku. 4<\/a>N\u00e1sledn\u00fd v\u00fdvoj vedl k v\u00fdvoji \u201et\u0159\u00edcestn\u00fdch\u201c katalyz\u00e1tor\u016f, kter\u00e9 se objevily v 80. letech 20. stolet\u00ed a zp\u016fsobily revoluci v regulaci emis\u00ed t\u00edm, \u017ee se sou\u010dasn\u011b zam\u011b\u0159ily na v\u0161echny t\u0159i hlavn\u00ed zne\u010di\u0161\u0165uj\u00edc\u00ed l\u00e1tky: CO, HC a NOx. 5<\/a>Tato zpr\u00e1va se pono\u0159\u00ed do odli\u0161n\u00fdch princip\u016f, funkc\u00ed, struktur\u00e1ln\u00edch inovac\u00ed a regula\u010dn\u00edch faktor\u016f, kter\u00e9 odli\u0161uj\u00ed tyto dva z\u00e1kladn\u00ed typy katalyz\u00e1tor\u016f.<\/p>\n\n\n\n Dvoucestn\u00e9 katalyz\u00e1tory, zn\u00e1m\u00e9 tak\u00e9 jako oxida\u010dn\u00ed katalyz\u00e1tory, p\u0159edstavovaly prvn\u00ed krok k \u0161irok\u00e9mu vyu\u017eit\u00ed automobilov\u00fdch v\u00fdfukov\u00fdch syst\u00e9m\u016f. Jejich prim\u00e1rn\u00ed funkc\u00ed je usnadnit specifick\u00e9 oxida\u010dn\u00ed reakce, p\u0159em\u011bnit dva z nejroz\u0161\u00ed\u0159en\u011bj\u0161\u00edch \u0161kodliv\u00fdch v\u00fdfukov\u00fdch plyn\u016f na m\u00e9n\u011b toxick\u00e9 formy.<\/p>\n\n\n\n Z\u00e1kladn\u00ed chemick\u00e9 procesy v obousm\u011brn\u00e9m konvertoru zahrnuj\u00ed kombinaci kysl\u00edku s oxidem uhelnat\u00fdm a nesp\u00e1len\u00fdmi uhlovod\u00edky. Hlavn\u00ed reakce jsou:<\/p>\n\n\n\n Tyto reakce jsou exotermick\u00e9, co\u017e znamen\u00e1, \u017ee uvol\u0148uj\u00ed teplo, kter\u00e9 zp\u016fsobuje zv\u00fd\u0161en\u00ed teploty v\u00fdfukov\u00fdch plyn\u016f p\u0159i pr\u016fchodu katalyz\u00e1torem, co\u017e vy\u017eaduje pou\u017eit\u00ed tepeln\u00fdch \u0161t\u00edt\u016f. 6<\/a>.<\/p>\n\n\n\n Dvoucestn\u00e9 p\u0159evodn\u00edky obvykle pou\u017e\u00edvaj\u00ed drah\u00e9 kovy, jako nap\u0159\u00edklad platina (Pt)<\/strong> a palladium (Pd)<\/strong> jako prim\u00e1rn\u00ed katalytick\u00e9 materi\u00e1ly 6<\/a>Tyto kovy velmi \u00fa\u010dinn\u011b podporuj\u00ed v\u00fd\u0161e popsan\u00e9 oxida\u010dn\u00ed reakce. Konvertor pracuje efektivn\u011b s relativn\u011b chudou sm\u011bs\u00ed paliva, co\u017e znamen\u00e1, \u017ee ve v\u00fdfukov\u00fdch plynech je p\u0159ebytek kysl\u00edku, kter\u00fd usnad\u0148uje oxida\u010dn\u00ed procesy. 6<\/a>.<\/p>\n\n\n\n Navzdory jejich \u00fa\u010dinnosti p\u0159i sni\u017eov\u00e1n\u00ed emis\u00ed CO a HC je z\u00e1kladn\u00edm omezen\u00edm dvoucestn\u00fdch katalyz\u00e1tor\u016f jejich neschopnost redukovat oxidy dus\u00edku (NOx)<\/strong> 6<\/a>Slou\u010deniny NOx se tvo\u0159\u00ed p\u0159i vysok\u00fdch teplot\u00e1ch spalov\u00e1n\u00ed a v\u00fdznamn\u011b p\u0159isp\u00edvaj\u00ed ke vzniku kysel\u00fdch de\u0161\u0165\u016f a fotochemick\u00e9ho smogu. Chemick\u00e9 prost\u0159ed\u00ed pot\u0159ebn\u00e9 pro redukci NOx (reduk\u010dn\u00ed atmosf\u00e9ra neboli nedostatek p\u0159ebyte\u010dn\u00e9ho kysl\u00edku) je v rozporu s oxida\u010dn\u00edm prost\u0159ed\u00edm nezbytn\u00fdm pro p\u0159em\u011bnu CO a HC. Toto inherentn\u00ed konstruk\u010dn\u00ed omezen\u00ed znamenalo, \u017ee obousm\u011brn\u00e9 konvertory mohly \u0159e\u0161it pouze dv\u011b ze t\u0159\u00ed hlavn\u00edch regulovan\u00fdch zne\u010di\u0161\u0165uj\u00edc\u00edch l\u00e1tek.<\/p>\n\n\n\n Dvoucestn\u00e9 m\u011bni\u010de se \u0161iroce pou\u017e\u00edvaly u benz\u00ednov\u00fdch automobil\u016f od poloviny 70. let 20. stolet\u00ed v n\u00e1vaznosti na na\u0159\u00edzen\u00ed z\u00e1kona o \u010dist\u00e9m ovzdu\u0161\u00ed. 6<\/a>Jejich neschopnost kontrolovat emise NOx v\u0161ak rychle vedla k jejich zastar\u00e1v\u00e1n\u00ed v benz\u00ednov\u00fdch vozidlech, proto\u017ee emisn\u00ed p\u0159edpisy se staly p\u0159\u00edsn\u011bj\u0161\u00edmi. 6<\/a>.<\/p>\n\n\n\n Je zaj\u00edmav\u00e9, \u017ee dvoucestn\u00e9 katalyz\u00e1tory, \u010dasto ozna\u010dovan\u00e9 jako Oxida\u010dn\u00ed katalyz\u00e1tory pro naftu (DOC)<\/strong>, se st\u00e1le pou\u017e\u00edvaj\u00ed ve vzn\u011btov\u00fdch motorech 7<\/a>Je to proto, \u017ee v\u00fdfukov\u00e9 plyny vzn\u011btov\u00fdch motor\u016f jsou ze sv\u00e9 podstaty bohat\u00e9 na kysl\u00edk, co\u017e \u010din\u00ed t\u0159\u00edcestn\u00e9 katalyz\u00e1tory nevhodn\u00fdmi. DOC v dieselov\u00fdch aplikac\u00edch oxiduj\u00ed CO, HC a tak\u00e9 usnad\u0148uj\u00ed oxidaci oxidu dusnat\u00e9ho (NO) na oxid dusi\u010dit\u00fd (NO2) a mohou sni\u017eovat hmotnost emis\u00ed pevn\u00fdch \u010d\u00e1stic oxidac\u00ed uhlovod\u00edk\u016f adsorbovan\u00fdch na uhl\u00edkov\u00fdch \u010d\u00e1stic\u00edch. 7<\/a>I kdy\u017e jsou u modern\u00edch benz\u00ednov\u00fdch automobil\u016f v regionech s p\u0159\u00edsn\u00fdmi emisn\u00edmi normami vz\u00e1cn\u00e9, lze je st\u00e1le nal\u00e9zt na m\u00e9n\u011b regulovan\u00fdch trz\u00edch, stejn\u011b jako u autobus\u016f na CNG, motocykl\u016f a mal\u00fdch benz\u00ednov\u00fdch motor\u016f (nap\u0159. vy\u017e\u00edna\u010d\u016f). 7<\/a>.<\/p>\n\n\n\n N\u00e1stup t\u0159\u00edcestn\u00fdch katalyz\u00e1tor\u016f (TWC) znamenal v\u00fdznamn\u00fd krok vp\u0159ed v oblasti kontroly emis\u00ed automobil\u016f. \u0158e\u0161il kritick\u00e9 omezen\u00ed sv\u00fdch dvoucestn\u00fdch p\u0159edch\u016fdc\u016f sou\u010dasnou redukc\u00ed oxid\u016f dus\u00edku (NOx) a z\u00e1rove\u0148 oxidac\u00ed oxidu uhelnat\u00e9ho (CO) a uhlovod\u00edk\u016f (HC). T\u00e9to pokro\u010dil\u00e9 funkce je dosa\u017eeno komplexn\u00ed souhrou redoxn\u00edch reakc\u00ed a p\u0159esn\u00fdm \u0159\u00edzen\u00edm motoru.<\/p>\n\n\n\n Trojcestn\u00e9 katalyz\u00e1tory jsou navr\u017eeny tak, aby umo\u017e\u0148ovaly sou\u010dasn\u00fd pr\u016fb\u011bh t\u0159\u00ed odli\u0161n\u00fdch chemick\u00fdch reakc\u00ed:<\/p>\n\n\n\n Schopnost prov\u00e1d\u011bt oxida\u010dn\u00ed i reduk\u010dn\u00ed reakce sou\u010dasn\u011b v jednom za\u0159\u00edzen\u00ed je ur\u010duj\u00edc\u00ed charakteristikou a hlavn\u00ed v\u00fdhodou t\u0159\u00edcestn\u00e9ho konvertoru.<\/p>\n\n\n\n Sou\u010dasn\u00e1 \u00fa\u010dinnost t\u011bchto t\u0159\u00ed reakc\u00ed je kriticky z\u00e1visl\u00e1 na udr\u017eov\u00e1n\u00ed p\u0159esn\u00e9ho stechiometrick\u00fd pom\u011br vzduch-palivo (\u03bb = 1)<\/strong> ve spalovac\u00edm procesu motoru 1<\/a>U benz\u00ednu je tento pom\u011br p\u0159ibli\u017en\u011b 14,7 hmotnostn\u00edch d\u00edl\u016f vzduchu na 1 hmotnostn\u00ed d\u00edl paliva.<\/p>\n\n\n\n Pro udr\u017een\u00ed k\u0159ehk\u00e9 rovnov\u00e1hy pot\u0159ebn\u00e9 pro optim\u00e1ln\u00ed provoz TWC zahrnuj\u00ed modern\u00ed syst\u00e9my sofistikovan\u00e9 \u0159\u00eddic\u00ed mechanismy:<\/p>\n\n\n\n Typick\u00e9 katalyz\u00e1tory TWC se skl\u00e1daj\u00ed z kombinace platina (Pt), palladium (Pd) a rhodium (Rh)<\/strong> dispergovan\u00e9 na nosn\u00e9m materi\u00e1lu s vysokou povrchovou plochou, nej\u010dast\u011bji oxid hlinit\u00fd (Al2O3)<\/strong> 1<\/a>.<\/p>\n\n\n\n Dlouhodob\u00fd v\u00fdkon TWC m\u016f\u017ee b\u00fdt ovlivn\u011bn n\u011bkolika deaktiva\u010dn\u00edmi mechanismy:<\/p>\n\n\n\n \u00da\u010dinnost katalyz\u00e1tor\u016f, a\u0165 u\u017e dvoucestn\u00fdch nebo t\u0159\u00edcestn\u00fdch, je hluboce ovlivn\u011bna jejich vnit\u0159n\u00ed strukturou a sofistikovanou materi\u00e1lovou v\u011bdou, kter\u00e1 stoj\u00ed za jejich konstrukc\u00ed. Oba typy sice sd\u00edlej\u00ed z\u00e1kladn\u00ed strukturn\u00ed prvky, ale specifick\u00e9 slo\u017een\u00ed a uspo\u0159\u00e1d\u00e1n\u00ed se li\u0161\u00ed, aby umo\u017enily jejich p\u0159\u00edslu\u0161n\u00e9 chemick\u00e9 funkce.<\/p>\n\n\n\n Modern\u00ed katalyz\u00e1tory univerz\u00e1ln\u011b pou\u017e\u00edvaj\u00ed monolitick\u00e9 pr\u016ftokov\u00e9 podp\u011bry<\/strong>, charakterizovan\u00fd vo\u0161tinov\u00e1 struktura<\/strong> 14<\/a>Tato konstrukce maximalizuje povrch vystaven\u00fd v\u00fdfukov\u00fdm plyn\u016fm a z\u00e1rove\u0148 minimalizuje pokles tlaku.<\/p>\n\n\n\n Ten\/Ta\/To pl\u00e1\u0161\u0165<\/strong> je kl\u00ed\u010dovou slo\u017ekou, kter\u00e1 poskytuje vysok\u00fd povrch nezbytn\u00fd pro disperzi katalyz\u00e1tor\u016f z drah\u00fdch kov\u016f a usnad\u0148uje chemick\u00e9 reakce. Obvykle se nan\u00e1\u0161\u00ed jako okyselen\u00e1 vodn\u00e1 suspenze na substr\u00e1t, po n\u00ed\u017e n\u00e1sleduje su\u0161en\u00ed a kalcinace. 14<\/a>.<\/p>\n\n\n\n V\u00fdb\u011br a mno\u017estv\u00ed drah\u00fdch kov\u016f je pro funkci p\u0159evodn\u00edku z\u00e1sadn\u00ed. Tyto kovy jsou souhrnn\u011b ozna\u010dov\u00e1ny jako kovy platinov\u00e9 skupiny (PGM).<\/p>\n\n\n\n V\u00fdroba katalyz\u00e1tor\u016f zahrnuje p\u0159esn\u00e9 techniky povlakov\u00e1n\u00ed:<\/p>\n\n\n\n V\u00fdkon katalyz\u00e1toru se \u010dasem sni\u017euje v d\u016fsledku r\u016fzn\u00fdch faktor\u016f, v\u010detn\u011b tepeln\u00e9ho st\u00e1rnut\u00ed (sp\u00e9k\u00e1n\u00ed kovov\u00fdch \u010d\u00e1stic), chemick\u00e9 otravy (nap\u0159. slou\u010deninami s\u00edry, olovem) a zne\u010di\u0161t\u011bn\u00ed. 1<\/a>Inovace si kladou za c\u00edl zm\u00edrnit tyto dopady:<\/p>\n\n\n\n Z\u00e1kladn\u00ed rozd\u00edl mezi dvoucestn\u00fdmi a t\u0159\u00edcestn\u00fdmi katalyz\u00e1tory spo\u010d\u00edv\u00e1 v rozsahu sni\u017eov\u00e1n\u00ed emis\u00ed a provozn\u00edch parametrech pot\u0159ebn\u00fdch k jeho dosa\u017een\u00ed. Tato \u010d\u00e1st poskytuje podrobn\u00e9 srovn\u00e1n\u00ed jejich v\u00fdkonu v z\u00e1vislosti na r\u016fzn\u00fdch zne\u010di\u0161\u0165uj\u00edc\u00edch l\u00e1tk\u00e1ch, provozn\u00edch rozsaz\u00edch a aspektech \u017eivotnosti.<\/p>\n\n\n\n Oba typy p\u0159evodn\u00edk\u016f vy\u017eaduj\u00ed pro spu\u0161t\u011bn\u00ed minim\u00e1ln\u00ed teplotu, zn\u00e1mou jako teplota p\u0159i zhasnut\u00ed sv\u011btla<\/strong>.<\/p>\n\n\n\n Dlouhodob\u00fd v\u00fdkon a \u017eivotnost katalyz\u00e1tor\u016f je ovlivn\u011bna n\u011bkolika faktory:<\/p>\n\n\n\n2. Dvoucestn\u00e9 katalyz\u00e1tory: Principy a omezen\u00ed<\/h2>\n\n\n\n
2.1. Chemick\u00e9 principy a reakce<\/h3>\n\n\n\n
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2.2. Materi\u00e1ly katalyz\u00e1toru a provozn\u00ed podm\u00ednky<\/h3>\n\n\n\n
2.3. Inherentn\u00ed omezen\u00ed<\/h3>\n\n\n\n
2.4. \u017d\u00e1dosti a postupn\u00e9 vy\u0159azov\u00e1n\u00ed<\/h3>\n\n\n\n
3. Trojcestn\u00e9 katalyz\u00e1tory: Pokro\u010dil\u00e1 chemie a funk\u010dnost<\/h2>\n\n\n\n
3.1. Sou\u010dasn\u00e9 redoxn\u00ed reakce<\/h3>\n\n\n\n
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3.2. Kl\u00ed\u010dov\u00e1 role stechiometrick\u00e9 regulace pom\u011bru vzduch-palivo<\/h3>\n\n\n\n
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3.3. Kapacita skladov\u00e1n\u00ed kysl\u00edku (OSC) a zp\u011btnovazebn\u00ed \u0159\u00edzen\u00ed<\/h3>\n\n\n\n
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3.4. Slo\u017een\u00ed katalyz\u00e1toru a teplota zhasnut\u00ed<\/h3>\n\n\n\n
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3.5. Mechanismy deaktivace katalyz\u00e1toru<\/h3>\n\n\n\n
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4. Konstruk\u010dn\u00ed a materi\u00e1lov\u00e9 inovace<\/h2>\n\n\n\n
4.1. N\u00e1vrh a materi\u00e1ly substr\u00e1tu<\/h3>\n\n\n\n
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4.2. Slo\u017een\u00ed a funkce washcoatu<\/h3>\n\n\n\n
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4.3. Slo\u017een\u00ed katalyz\u00e1tor\u016f na b\u00e1zi drah\u00fdch kov\u016f<\/h3>\n\n\n\n
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4.4. V\u00fdrobn\u00ed procesy<\/h3>\n\n\n\n
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4.5. Inovace v oblasti st\u00e1rnut\u00ed katalyz\u00e1tor\u016f a trvanlivosti<\/h3>\n\n\n\n
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5. Srovn\u00e1vac\u00ed \u00fa\u010dinnost sni\u017eov\u00e1n\u00ed emis\u00ed a provozn\u00ed charakteristiky<\/h2>\n\n\n\n
5.1. V\u00fdkonnost v oblasti sni\u017eov\u00e1n\u00ed emis\u00ed<\/h3>\n\n\n\n
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5.2. Rozsahy provozn\u00edch teplot a doby zhasnut\u00ed sv\u011btla<\/h3>\n\n\n\n
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5.3. Trvanlivost a degradace syst\u00e9mu<\/h3>\n\n\n\n
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