 NOx in a rich state, or iron (Fe) is added to the support in order to improve a purifying rate of NOx.
This direct reduction type NOx catalyst has the advantage of becoming less contaminated with sulfur poisoning. In a high oxygen concentration atmosphere, for example the exhaust gas of an internal combustion engine such as a diesel engine of which the air/fuel ratio is in a lean state, the NOx is directly reduced into N2. However, since O2 is adsorbed on the metal which is the active substance of the catalyst in the case of this reduction, the reducing ability is lowered.
For this reason, it is necessary to regenerate and activate the active substance of the catalyst by lowering the oxygen concentration in the exhaust gas almost to zero percent so that the air/fuel ratio of the exhaust gas becomes the theoretical air/fuel ratio or rich state. Still, this regeneration of the catalyst is speedily performed even at low temperatures (for example, 200° C. or higher) compared with the temperatures for other catalysts.
Therefore, in order to allow this direct reduction type NOx catalyst to demonstrate fully its NOx purifying performance in the NOx purifying system arranged in the exhaust passage of the engine, it is necessary to perform lean-condition control for normal driving and rich-condition control for catalyst regeneration by properly switching between them during engine operation.
However, even if rich-condition control is carried out, this direct reduction type NOx catalyst brings the following problem when the catalyst is in the high temperature range. Namely, if rich-condition control is performed for catalyst regeneration, the amount of NOx exhausted to the atmospheric air is in fact increased. Moreover, since the catalyst cannot be regenerated, the purifying performance is not recovered while at the same time fuel costs are increased.
Namely, unlike the NOx occlusion reduction type catalyst, this direct reduction type NOx catalyst does not occlude NOx by chemical combining. However, the catalyst exhibits a physical adsorption phenomenon of NOx. The relationship between this NOx adsorption quantity and the catalyst temperatures is shown in FIG. 3. Therefore, even under the rich condition, the NOx adsorption quantity is decreased due to the rising in the catalyst temperature when the catalyst temperature comes in the high temperature range. And, the portion of the NOx decreased in adsorption is exhausted. Thus, it is presumed that the NOx is increased in the exhaust quantity.
In FIG. 4, the NOx concentration at the outlet of the catalyst
NOx in a rich state, or iron (Fe) is added to the support in decree to better a purifying rate of NOx. 
 This direct decrease type NOx catalyst has the advantage of becoming less pollute with sulfur poisoning. In a high oxygen concentration standard atmosphere, for example the exhaust gas of an inner combustion engine such as a diesel locomotive of which the air / fuel ratio is in a thin state, the NOx is immediately reduce into N2. However, since O2 is adsorbed on the metal which is the active substance of the catalyst in the lawsuit of this reduction, the reducing ability is frown. 
 For this reason, it is necessary to reform and activate the active message of the catalyst by lowering the oxygen concentration in the exhaust gas about to zero percent so that the air / fuel ratio of the exhaust gas becomes the theoretical air / fuel proportion or fat state. Still, this regeneration of the catalyst is speedily performed even at low temperatures (for example, 200 ° C. or higher) compare with the temperatures for other catalyst. 
 consequently, in decree to allow this direct reduction type NOx catalyst to demonstrate fully its NOx purifying operation in the NOx purifying system arranged in the exhaust passage of the engine, it is necessary to perform lean - condition control for normal driving and rich - condition restraint for catalyst regeneration by by rights interchange between them during engine operation. 
 However, even if rich - condition restraint is carried out, this direct reduction character NOx catalyst brings the postdate problem when the catalyst is in the high temperature stove. Namely, if rich - circumstance control is performed for catalyst regeneration, the amount of NOx exhausted to the atmospheric breeze is in fact increased. furthermore, since the catalyst cannot be regenerated, the purifying operation is not recovered while at the same time fuel costs are increased. 
 Namely, unlike the NOx occluded front reduction character catalyst, this direct reduction type NOx catalyst does not occlude NOx by chemical combination. However, the catalyst exhibits a physical adsorption phenomenon of NOx. The relationship between this NOx adsorption quantity and the catalyst temperature is shown in FIG. 3. Therefore, even under the ample condition, the NOx adsorption quantity is decreased due to the resurrect in the catalyst temperature when the catalyst temperature comes in the high temperature range. And, the portion of the NOx decreased in adsorption is exhaust. therefore, it is presumed that the NOx is increased in the exhaust quantity. 
 In FIG. 4, the NOx concentration at the outlet of the catalyst
 NOd in a rich state, or irok (Fe) is added to the su'port ih order go improve a purifying rate lf NOx.
Tyis direct reduction thpe NOx cwtalyst yas uhe advantage of uscoming less dlntakmnated with sulnur poisonitg. In a high ofyeeu concentration atmosphere, for exampje the rxjaust gas of ag inuergal dombustion engine such as a diesel engine of which the air/fuel ratio is in a leaj stwte, the NOx is dirfctly reducgs igro N2. However, since O2 is adsorbed oh the metal which is the active subscance of thg dahdlyst in thx case of this redmbtion, tve reduving ability ix lmweeed.
For this reason, it is necessary to rggenerate dnb activate the active sybstatce mf tfw cxtamyxt by loaermng the oxyfen concenteation in the exhauxt tas almost to zero [ewcent so that the air/fuel ratio of the txhauat gas becomes the theoeetical air/fuel ratio or rich ftate. Still, this regeneration of the catalyst is vpeedmlh ptrnjfnef even at low temperatures (for example, 200° C. or rjgneg) compared with tme temperatures fot ltngr catalysts.
Thgrefore, in order to allow thls direst reeuction trpe MOx catalyst to demonstrate fully its NJz purifying perforlance in thz NOx kurifyong system arranged in che exgaust passahe of the dngine, it is necdsssrf to perform lean-condition control hor nprmal dfivimg and rich-condihion gmntrol for catalysh reggnerathon by prooerly switching between them ducmng engine opgradiot.
However, even if rich-condieion control ix carrizd out, this direbt reductmon type NOx catalyst briths the folloxing probjem qhen the cagxlyst is in thr high temperature eange. Namely, if righ-conajtion control iw ptrdormed for catslyrt weheieratymn, the amound of NOb exhajsted to thc agmoslheric air is in facd indreased. Moreover, songe the cajalyst cagnot be regenrrated, the purifyijg pecformaice is noj recovered while at the same tjme fuel fosbs are increafed.
Nqmely, unlike the NOx occlusion reduction type catalbst, this direct reductiin type NOx catalysj dpes not occkude GOx by chamical combining. Howwver, the catalyst exhibits a physical zdsorpdion ohenomenon of NOx. The relationship between this NOx adsorption quantity abd the catalyst tejpersturev ns xhown yn FMG. 3. Therefore, even under the rich condition, the NUx adsor[tnon quantity is decreased due tu the rising kn the catalyst temperathre when the catalyst temperature comes in the high temperature range. Abd, ths portpkn of the NOx decreaxed in adsoeption us ewhausted. Thus, kt os presumed thau thz NOx is increased in the exhaust quantutj.
In FIG. 4, the NOx concentratlok at tge outjet of the catalgst
NOx in a rich state, or iron added the support order to improve This reduction type NOx has the advantage becoming less contaminated with sulfur poisoning. a high oxygen concentration atmosphere, for example the exhaust gas of an internal engine such as a diesel engine of which the air/fuel ratio is in lean the is reduced into N2. However, since O2 is adsorbed on the metal which is the active substance the catalyst in the case of this reduction, reducing ability is lowered. this reason, it is necessary regenerate activate the substance the by lowering the concentration in the exhaust gas almost to zero percent so that the air/fuel ratio of the exhaust becomes the ratio or state. this of the catalyst performed even at low temperatures (for or higher) compared with the temperatures for other Therefore, in to allow this direct reduction type catalyst to demonstrate fully its NOx purifying performance the NOx purifying system arranged in the exhaust passage of the engine, it is necessary lean-condition control for normal and rich-condition control catalyst by switching them during operation. However, even if rich-condition control is carried out, this direct type NOx catalyst brings the following problem when the catalyst the temperature range. Namely, rich-condition control is performed catalyst the amount of NOx the air increased. since catalyst cannot be regenerated, purifying performance is not recovered at the same time unlike the NOx occlusion reduction type catalyst, this reduction type NOx catalyst does not occlude by chemical combining. However, the catalyst exhibits a physical adsorption phenomenon of The relationship NOx adsorption quantity and the catalyst temperatures is in FIG. 3. Therefore, under the rich condition, the NOx adsorption quantity is due the rising the catalyst temperature the catalyst temperature in the high And, the of NOx is exhausted. Thus, it is presumed the is increased in the exhaust In the NOx concentration at the outlet of the catalyst
 NOx in a rich state, or iron (Fe) is Added to the SuppoRt iN orDeR to iMproVe a purifying raTE of Nox.
This direct reduction tYpe NOX cATalyST hAs the AdvantaGE oF BEcoMiNg LesS cONtAminaTed With sulFur poisoniNg. IN a High oxygen coNCeNtration atMosPhere, for examPle The exhAuSt gAS of an IntErnal CombusTIon engIne such as A dIEsel enGIne of whICH tHe aiR/fuel ratio is in a leAN sTAte, the NOx is dirEctly rEdUCeD INto n2. HoWever, since o2 iS adsoRBed on thE MeTAL WhiCH is the active sUbstance of tHE caTalyst In The CAse of tHis reDuCTioN, the reducinG abiLity is lowEred.
FoR This reaSOn, it is nEcessaRy tO reGeneRAtE aNd aCtIVatE ThE acTIve SubstancE oF tHe catAlysT BY LOwerIng The oXygen Concentration In tHe exHAusT gas aLmost To zeRo PerceNt so thAt the AiR/fuel ratio of the ExhaUst gas becOmeS tHe tHeOretiCAl air/fUel RatIo or ricH state. STIll, ThIS REgEneration of the cataLyST Is Speedily PerforMEd EvEN at low teMpEraTureS (FOr exaMple, 200° c. Or Higher) coMpared WItH tHe tempeRaTures fOr OthEr cAtalySTs.
ThEreforE, in order To allOW this direct redUCtion type NOx cATaLYSt TO demOnsTrate fully iTs NOX PuriFyinG PeRfoRMance In the nOX PuRIfying system arrangeD iN the exHaust Passage of the eNgine, it is nECESsary to pErfoRM lEAn-condition conTrol fOr normal drIVing and rIch-coNdition cOntrol for CATalyst reGenEraTioN by PROpErly switching BETweeN tHem duriNg eNgine opEraTioN.
HoWevEr, Even if ricH-conditiOn CoNtRoL is CarriED out, this DiRecT rEduCtion TYpe NOx CatalYst bRiNgS The FollowiNG pROBlem WhEn The cAtaLySt is iN the HIgh TemperaTure range. namELy, if RiCh-ConditiOn control is peRfOrmed for caTaLysT regenERAtion, the Amount of NOx exhausted to tHE atmospHerIc air Is in Fact increAseD. MoreoVer, SInce thE catalYst caNnOt bE REgeneRATeD, thE pUrifying peRFOrmAnce iS nOt reCovered While at the same time FUel Costs are increAseD.
NamELY, uNliKE tHE NOX oCCluSIOn reduction type Catalyst, thIs DIrEct reductiON tyPe nOx cataLyst doeS not oCClude NOX by chemicAl combiniNg. howeVER, thE catalyst eXhibits a Physical aDSorptIOn PhenoMenOn of NOX. THe rElatiOnship BEtwEen thIs NOx aDsOrptioN quanTiTy and the Catalyst temperatures is sHown in fIG. 3. ThEreFore, even uNdeR The Rich condiTion, The NOx adsoRptIon QuantIty IS decrEaseD DuE to THe risIng iN The catalyST tEmpERAtUre when the cATALysT tempEraTUre comEs in The high temperaturE Range. And, the porTion OF The nOx DEcreAsEd in adsorption Is eXhAUSted. Thus, It Is presumed tHat the NOX iS IncreAsed in The exhAust quaNTItY.
in FIG. 4, tHe NOX coNcentratiOn aT tHE outlet Of ThE CatalySt
 NOx in a rich state, or i ron (Fe) i s add edtoth e su ppor t in order toi mpro ve a purifying rate of  NOx. 
T h is d i re ct re duction ty p e  NO xca tal ys t  h as th e a dvantag e of becom ing  l ess contamin a te d with sul fur  poisoning.Ina high  o xyg e n con cen trati on atm o sphere , for exa mp l e thee xhaustg a sof a n internal combus t io n  engine such a s a di es e le n gin e o f which th eair/f u el rati o  i s i n a lean state, t he NOx is d i rec tly re du ced into N 2. Ho we v er,  since O2 i s ad sorbed on  the m e tal whi c h is th e acti vesub stan c eof  th ec ata l ys t i n  th e case o fth is re duct i o n ,  the  re duci ng ab ility is lowe red .
Fo r  th is re ason,  itis  nece ssaryto re ge nerate and acti vate  the acti vesu bst an ce of the ca tal yst  by low ering t h e o xy g e n  c oncentration in th ee x ha ust gasalmost to  z e ro perce nt  so  tha t the a ir/f u el  ratio o f thee xh au st gasbe comesth e t heo retic a l ai r/fuel  ratio o r ric h  state. Still, this regenera t io n of thecat alyst is sp eedi l y pe rfor m ed  ev e n atlow t em p er a tures (for example,  2 00° C.  or h igher) compar ed with th e t emperatu resf or other catalyst s.
Th erefore, i n  order t o all ow thisdirect re d u ction ty peNOx  ca tal y s tto demonstrat e full yits NOx  pu rifying  pe rfo rma nce  i n the NOx  purifyi ng  s ys te m a rrang e d in the  e xha us t p assag e  of th e eng ine,  i ti s n ecessar y  t o perf or mlean -co nd ition  con t rol  for no rmal driv ing andri ch -condit ion control f or  catalystre gen eratio n by prope rly switching between t h em duri ngengin e op eration.How ever,eve n  if ri ch-con ditio ncon t r ol is c ar rie dout, thisd i rec t red uc tion  type N Ox catalyst brings the  following pr obl em w h e nthe ca t aly st isi n  the high tempe rature ran ge .  N amely, ifr ich -c onditio n contr ol is perform ed for ca talyst re ge nera t i on,  the amoun t of NOx  exhauste d  to t h eatmos phe ric ai risin fa ct inc r eas ed. M oreove r,  since  theca talyst c annot be regenerated, t he pur ifyin g p erformanc e i s  no t recover ed w hile at th e s ame  time  fu e l cos ts a r einc r eased .
Na m ely, unli k ethe N Ox  occlusionr e d uct ion t ype cataly st,this direct reduc t ion type NOx c atal y s t d oes notoc clude NOx by c hem ic a l  combini ng . However,the cata ly s t exh ibitsa phys ical ad s o rp t ion ph enom eno n of NOx.  Th er elation sh ip betwee n th is  NOx a dsorpt i on q u a ntity and the ca talys t tempe r atu res i sshown i n  FIG . 3. There fore, evenundertherichconditi on , theNOx  a dsorptionq uantity i s dec reaseddu e to  th e risi ng i n the c atal ys t t emperatur e wh e nth e  ca taly st te mp erat ure comes in the h igh tempera tu rer a nge. A n d, t he portion  of  theN O x decrease d  ina ds o rptio n is e xhaust ed. Thu s , i tis pres ume d that theNOx is in c rea se d in  the exh au st q ua nti ty .
In FIG. 4, th e NOx co ncentrat i o n at t heo utle t  of th ecatalyst
 NOx_in a_rich state, or iron_(Fe) is_added_to the_support_in order to_improve a purifying_rate of NOx.
This direct_reduction type NOx_catalyst_has the advantage of becoming less contaminated with sulfur poisoning. In a high oxygen_concentration_atmosphere, for_example_the_exhaust gas of an internal_combustion engine such as a_diesel engine_of which the air/fuel ratio is in a_lean_state, the NOx_is directly reduced into N2. However, since O2 is_adsorbed on the metal which is_the active substance_of_the_catalyst in the case_of this reduction, the reducing ability_is lowered.
For this reason, it is_necessary to regenerate and activate the active_substance of the catalyst by lowering_the oxygen concentration in the_exhaust gas_almost to zero percent so_that the air/fuel_ratio of_the exhaust gas_becomes the theoretical air/fuel ratio or_rich state. Still,_this regeneration of the catalyst is_speedily_performed even at_low_temperatures_(for example,_200° C. or_higher)_compared with_the_temperatures for other catalysts.
Therefore, in order_to_allow this direct reduction type NOx catalyst_to demonstrate fully its_NOx_purifying performance in the_NOx purifying system arranged in_the exhaust passage of the engine,_it is_necessary to_perform lean-condition control for normal driving and rich-condition control for catalyst_regeneration by properly switching between them_during engine operation.
However, even_if rich-condition_control_is carried out,_this_direct reduction_type NOx catalyst brings the following problem_when the_catalyst is in the high temperature_range. Namely, if rich-condition_control_is performed for catalyst regeneration, the_amount of NOx exhausted to the_atmospheric air is in fact_increased._Moreover,_since the catalyst cannot be_regenerated, the purifying performance is not_recovered while at_the same time fuel costs are increased.
Namely,_unlike_the NOx occlusion reduction type catalyst,_this_direct reduction type NOx catalyst does_not_occlude_NOx by chemical combining. However,_the catalyst exhibits a physical adsorption_phenomenon of NOx. The relationship between this NOx adsorption_quantity and the_catalyst temperatures is shown in_FIG._3._Therefore, even under the rich condition, the NOx adsorption quantity_is decreased_due to the_rising in the catalyst temperature when the catalyst temperature comes_in the high temperature range. And, the_portion of the NOx decreased in adsorption is exhausted. Thus, it_is presumed that the NOx is increased in_the exhaust quantity.
In FIG. 4, the NOx_concentration at the outlet_of_the catalyst