Photocatalytic reactor

Abstract

A photocatalytic reactor ( 30 ) for treating exhaust gases from a power plant such as an internal combustion engine, which reactor comprising a chamber ( 36 ) for receiving a flowing exhaust gas, a first inlet ( 32 ) and a first outlet ( 34 ), at least one source of electromagnetic radiation ( 38 ) and at least one substrate monolith ( 10 ) for supporting a photocatalyst disposed in the chamber, characterised in that the substrate ( 10 ) comprises at least one passage ( 20 ) defined in part by a wall ( 12 ′), which wall comprising at least a one second inlet ( 13 ) and at least one second outlet ( 14 ), wherein the sum of the cross-sectional areas of the or each second outlet ( 14 ) being greater than the sum of the cross sectional areas of the or each second inlet ( 13 ) whereby the linear flow velocity of a gas at a point downstream of the at least one second outlet ( 14 ) is less than the linear flow velocity of the gas entering the at least one second inlet ( 13 ).

1 . A photocatalytic reactor for treating exhaust gases from a power plant such as an internal combustion engine, which reactor comprising a chamber for receiving a flowing exhaust gas, a first inlet and a first outlet, at least one source of electromagnetic radiations, at least one monolith disposed in the chamber and a photocatalyst characterised in that the monolith comprises at least one walled body defining a passage, which at least one walled body comprising at least one second inlet and at least one second outlet, wherein the sum of the cross-sectional areas of the or each second outlet being greater than the sum of the cross sectional areas of the or each second inlet whereby the linear flow velocity of a gas at a point downstream of the at least one second outlet is less than the linear flow velocity of the gas entering the at least one second inlet.  
     
     
         2 . A reactor according to  claim 1 , wherein the cross sectional area of the or each passage is greater towards a downstream end relative to an upstream end.  
     
     
         3 . A reactor according to  claim 1 , wherein the at least one walled body comprises two or more walled bodies wherein each walled body has a second inlet and all passages have at least one second outlet.  
     
     
         4 . A reactor according to  claim 1 , wherein the or each passage comprises a tube.  
     
     
         5 . A reactor according to  claim 4 , wherein the tube is frustoconical.  
     
     
         6 . A reactor according to  claim 1 , wherein the passage is further defined by at least one baffle.  
     
     
         7 . A reactor according to  claim 6 , wherein the baffle is a narrowing or constriction of the passage.  
     
     
         8 . A reactor according to  claim 7 , wherein the narrowing or constriction of the passage comprises a venturi tube.  
     
     
         9 . A reactor according to  claim 6 , wherein the at least one baffle forms a dead-end in the passage.  
     
     
         10 . A reactor according to  claim 1 , wherein the or each second outlet is positioned so that a gas can exit the at least one passage in a direction other than that in which it enters the at least one passage.  
     
     
         11 . A reactor according to  claim 1 , wherein an internal surface of the chamber supports the photocatalyst.  
     
     
         12 . A reactor according to  claim 11 , wherein an internal surface of the at least one walled body supports a photocatalyst.  
     
     
         13 . A reactor according to  claim 1 , further comprising means for supporting the photocatalyst in the flow path of exhaust gas exiting the at least one second outlet.  
     
     
         14 . A reactor according to  claim 13 , wherein the support means includes an internal surface of a sleeve disposed around the at least one walled body.  
     
     
         15 . A reactor according to  claim 13 , wherein the support means comprises at least one substantially lateral projection extending into a space on the exterior of the at least one walled body relative to the passage.  
     
     
         16 . A reactor according to  claim 15 , wherein the at least one projection is supported by the exterior of the at least one walled body.  
     
     
         17 . A reactor according to  claim 15 , wherein the support means comprises at least one fin.  
     
     
         18 . A reactor according to  claim 17 , wherein the at least one fin extends in a helix in the longitudinal direction relative to the passage.  
     
     
         19 . A reactor according to  claim 1 , wherein the at least one walled body is made, at least in part, from a metal.  
     
     
         20 . A reactor according to  claim 1 , wherein the passage is of substantially circular cross-section.  
     
     
         21 . A reactor according to  claim 1 , wherein the photocatalyst is selected from the group consisting of TiO 2 , SnO 2 , CdS, CdSe, ZnS, In 2 S 3 , In 2 Se 3 , SrTiO 3 , alpha-Fe 2 O 3 , SiO 2 /Al 2 O 3 , ZnO, CdTe, CuInSe 2 , CuS, FeS 2 , CuFeS 2 , Si, GaAS, GaSb, GaPS, GaInP, As 2 S 3 , AlP, AlAg, GaP, AlSb, InP, InAS, InSb, MoS 2 , WTe 2 , Cr 2 Te 3 , MoTe, Cu 2 S, WS 2 , Bi 2 O 3 , CuO, Cu 2 O, MoO 3 , InO 3 , Ag 2 O, PbO, SrTiO 3 , BaTiO 3 , CO 3 O 4 , Fe 2 O 3 , NiO, natural or synthetic pyrites, natural or synthetic chalcopyrites, and mixtures of any two or more thereof.  
     
     
         22 . A reactor according to  claim 21 , wherein the photocatalyst further comprises one or more transition metal dopant.  
     
     
         23 . A reactor according to  claim 21 , wherein the photocatalyst further comprises one or more precious metal dispersed on the material.  
     
     
         24 . A reactor according to  claim 1 , wherein the or each sources of the electromagnetic radiation emits UV, broad band visible or infrared electromagnetic radiation.  
     
     
         25 . A reactor according to  claim 1 , wherein the or each electromagnetic radiation source is disposed inside the chamber.  
     
     
         26 . An exhaust system for a vehicle powered by a power plant, which exhaust system including a reactor according to  claim 1 .  
     
     
         27 . An exhaust system for a diesel engine according to  claim 33 , which exhaust system including a catalyst for oxidising NO to NO 2 , a downstream particulate filter for trapping particulate matter, wherein the particulate matter combusts in NO 2  in the exhaust gas at up to 400° C. and the reactors is disposed downstream of the particulate filter.  
     
     
         28 . An exhaust system according to  claim 26 , further comprising an electronic control unit for controlling the function of the exhaust system.  
     
     
         29 . A method of photocatalytically reducing NO x  in a flowing gas, which method the steps of reducing, in any dimension, the linear flow rate of the gas by passing the exhaust gas through a substrate comprising at least one passage defined in part by a wall, which wall comprising at least one second inlets and at least one second outlets, wherein the sum of the cross-sectional areas of the or each outlet being greater than the sum of the cross sectional areas of the or each inlet, contacting a photocatalyst with electromagnetic radiation, and contacting the photocatalyst with gas exiting the at least one outlet.  
     
     
         30 . (Canceled)  
     
     
         31 . (Canceled)  
     
     
         32 . A reactor according to  claim 1 , whereas the at least one walled body is made, at least in part, from stainless steel.  
     
     
         33 . An exhaust system according to  claim 26 , wherein the power plant is an internal combustion engine.  
     
     
         34 . A reactor according to  claim 1 , wherein the photocatalyst is the anatase form of TiO 2 .  
     
     
         35 . A reactor according to  claim 22 , wherein the transition metal dopant is selected from the group consisting of Cr(III), Fe(III), V(IV), Ti(III), Sb(V), Ga(III), Ag(I) and a mixture of any two or more thereof.  
     
     
         36 . A reactor according to  claim 23 , wherein the precious metal is selected from the group consisting of Pt, Pd, Rh, Ag, Au, and a mixture of any two or more thereof.  
     
     
         37 . The method according to  claim 29 , wherein the step of contacting the photocatalyst with a gas exiting the at least one outlet further comprises the step of reducing NOx in the gas by photocatalysing the oxidation of hydrocarbon and/or carbon monoxide with NOx and/or oxygen (O 2 ).  
     
     
         38 . The method according to  claim 27 , wherein the exhaust gas is from an internal combustion engine.