دانلود رایگان مقاله لاتین فوتوکاتالیست الحاق اکسیداسیون کربن از سایت الزویر
عنوان فارسی مقاله:
فوتوکاتالیست الحاق اکسیداسیون کربن همزمان و کاهش NOx
عنوان انگلیسی مقاله:
Photocatalysis assisted simultaneous carbon oxidation and NOx reduction
سال انتشار : 2017
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مقدمه انگلیسی مقاله:
1. Introduction
Controlled oxidation of carbon nanoparticles is of interest to many practical applications. Regeneration of diesel particulate filters is a prominent example. A common filter regeneration strategy involves oxidation of the carbon deposit using NO2 obtained by catalytic oxidation of NO emitted by the engine [1]. NO2 mediated carbon oxidation proceeds at temperatures exceeding 250 ◦C, and NO2 is reduced mainly to NO rather than N2, necessitating an additional DeNOx system downstream from the filter [1]. In nanotechnology, oxidative modification of carbon nanomaterials is needed for selective elimination of amorphous carbon debris, and for altering physico-chemical properties such as enhancing hydrophilicity. To this purpose carbon nanotubes (CNTs) are oxidized with concentrated mineral acid (e.g. nitric acid and sulfuric acid) to facilitate dispersion in polar solvents [2,3]. Graphitic oxide obtained by oxidation of graphite with the mixture of strong oxidants (nitric acid, sulfuric acid or potassium permanganate) [4,5]. Improved methods have been reported, concentrated acid andstrong oxidants are necessary for the oxidation process [6,7]. More sustainable chemical methods would be welcome [6]. Photocatalytic oxidation is mentioned among the green chemistry methods for sustainable development [8]. The method has been used to oxidize carbon, and for converting NOx to N2 various ways, and the possibility of combining both reactions has been suggested. Titaniumdioxide is widely used for photocatalytic applications for its commercial availability and robustness [8]. UV light is needed for charge separation in TiO2 semiconductor because of the large band gap of crystalline TiO2 phases (anatase: 3.2 eV, rutile: 3.03 eV) [9]. Soot can be oxidized using sunlight-driven photocatalysis on TiO2. Self-cleaning properties of TiO2 coatings covered by soot have been demonstrated [10–16]. The efficiency of this photocatalytic process proceeding outdoors is, however, very low [10]. Oxidation of a 0.5 m soot deposit requires e.g. 45 days [10,17]. NOx elimination from air using photocatalysis is an emerging technology. Photocatalytic NOx oxidation converts NO with O2 to NO2, which reacts further to nitrates that can be removed from the photocatalyst by water leaching. This deNOx concept has been implemented e.g. on the surface of concrete pavement [18,19]. Titaniumdioxide whichisphotoactiveunder UVlight achievesphotodecomposition of NO to N2 and O2 [8]. The reaction is slow and inhibited by O2. Substantial N2O by-product formation is observed [20–22]. Modified TiO2 and zeolites have been investigated toimprove catalyst activity and N2 selectivity of the NO decomposition reaction with some success [23]. Additionally, the photo-SCR activity of commercial and modified TiO2 in the presence of sacrifi- cial reducing agents such as NH3, CO and short-chain hydrocarbon reductants has been demonstrated [24–32]. In nanotechnology, photocatalytic oxidation potentially is a sustainable method for the preparation of a variety of carbon materials such as oxidized carbon nanotubes and graphite oxide. In a previous publication we reported that carbon black can be selectively photo-oxidized to CO2 using NO in absence of O2 [33]. Under those conditions in absence of O2, NO was converted to N2. The observed carbon oxidation rate was relatively low (ca. 2 gcarbon/mgTiO2 h). In this paper we investigate the potential of photocatalytic oxidation of carbon using reactive gas mixtures with ppm quantities of NO in addition to O2. Promising results were obtained showing enhanced carbon oxidation rates and even oxidation of all carbon particles. Interestingly, NO is selectively reduced to N2 even in the presence of O2. The size reduction of carbon particles up on oxidation is monitored with HR SEM.
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کلمات کلیدی:
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