Research Article pubs.acs.org/journal/ascecg
Facile Synthesis of PtxNiy Catalyst Supported on Carbon for Low Temperature H2−SCR Bao-sheng Tu, Wei Sun, Yi-jun Xue, Waqas Qamar Zaman, Li-mei Cao, and Ji Yang* School of Resources and Environmental Engineering, State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, East China University of Science and Technology, No. 130 Meilong Road, Xuhui District, Shanghai 200237, PR China ABSTRACT: PtNi alloy nanoparticles supported on carbon (XC-72) are synthesized via a one-pot synthetic approach. This synthesized bimetallic composite offers several advantages, such as reduction of precious Pt along with an increase in activity due to the modified electronic structure. The prepared PtNi/C catalysts were employed as catalysts for NO removal both in a fixed-bed reactor and in a newly designed gas diffusion reactor. The performances of all prepared PtNi/C catalysts were higher than Pt/C at the same conditions and maintained a stable NO removal at a wide temperature window (100−300 °C), especially for Pt65Ni35 (more than 95% from 120 to 300 °C). This is attractive for low temperature SCR technology. According to XPS analysis, the surface layer phase was comprised of Pt contents with Ni being localized beneath the successive layers until Ni content increased to 67% mole ratio. The surface presence of Ni significantly affects the Pt electronic structure and raises the mass specific activity of Pt. Meanwhile, PtNi/C catalysts were introduced in a new gas diffusion reactor to remove NO under quantitatively less catalysts (30 mg), high NO concentration (1000 ppm), and at a high flow rate (resulting in a very short residence time of 0.09 s) condition. NO removal reaches almost 100% below 95 °C for all the PtNi catalysts and among all Pt65Ni35 exhibited the best performance. In addition, the influence of SO2 on the performance of Pt65Ni35 was also investigated, and the catalysts exposed a good antipoisonous property. The excellent performance of PtNi catalysts and a gas diffusion reactor are strongly recommended for their utilization as highly active and economical technology for NO removal. KEYWORDS: H2−SCR, PtNi, NOx, Gas diffusion
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INTRODUCTION An increase in demand for higher quality of ambient air has stimulated vast research on pollutant control technologies that are economically feasible, environmentally benign, and highly efficient. NOx emissions can be regarded as the major threat for the atmospheric environment due to their enormous contribution in acid rain, photochemical fog, and even in the promotion of PM2.5.1,2 Consequently, for the reduction of NO emissions, development of effective technologies and efficient catalysts remain an area of wide concern for research studies all over the globe. Selective catalyst reduction (SCR) has been proven as an efficient method for employment of reducing agents.3,4 However, conventional reducing agents such as NH3, urea, and hydrocarbons (CHx) can cause many negative effects like NH3 slipping, air heater fouling, CO2 production upon CHx burning, and higher operational cost during the process.5,6 Recently, hydrogen (H2) as a reducing agent for SCR (H2− SCR) technology has attracted growing interest due to its cheapness and unfavorable behavior toward greenhouse gas emissions.7−9 Another incomparable advantage for H2−SCR is that it can give high efficiency for NO removal in the pursuit of low temperature (T < 200 °C) catalysis,7 as lower temperature conditions decrease operational and capital costs and also © XXXX American Chemical Society
inhibit the arousal of a competitive reaction from residual oxygen in the flue stream.10 Therefore, based on these advantages the H2−SCR is considered as a breakthrough in NOx emissions control technologies. At present, the most extensively preferred H2−SCR catalysts are based upon the presence of noble group elements (Pt and Pd), especially Pt-based exhibit high activity at extremely low temperatures such as reported 1% Pt/Al2O3, 1% Pt/SiO2− Al2O3, 0.1% Pt/MgO-CeO2, et al.11−13 Even though various materials as support are employed for Pt-based catalysts, the Pt site plays the determined role in NO-H2 reaction for low temperature catalysis. Machida et al.14 and Costa et al.15 found that the conversion of NO with H2 is mainly processed on the Pt site rather than on supports. Another important point is that the oxidation state of Pt is the controlling factor for NO-H2 reaction activity,16 and the lower valence state of Pt may have the higher activity.14 As our previous studies on Pt doped Ni− Fe spinel oxides demonstrated, the Pt with different valence states favors NO adsorption on the Pt site.17 The investigation Received: February 22, 2017 Revised: April 25, 2017 Published: May 4, 2017 A
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 1. Schematic setup of the proposed reactor for NO removal. max2550 V apparatus with a Cu−Kα radiation source (λ = 1.5406 Å). The surface area of powders is determined by the Brunauer−Emmett− Teller (BET) method using Micromeritics Tristar 3020 SIN 993. The morphologies of the catalysts were observed using a field-emission scanning electron microscope (FESEM) equipped with a Nova NanoSEM and the energy dispersive X-ray (EDX) spectrometer to confirm the composition using a TEAMApollo system. A JEM-2100 transmission electron microscope was used to obtain the TEM and HRTEM images. The surface properties of the catalysts were determined via X-ray photoelectron spectroscopy (XPS) using an ESCALAB 250Xi instrument with an Al−Kα radiation source at an energy step size of 0.05 eV for high resolution XPS spectrum. The Xray absorption data (XAS) at the Ir LIII - edge of the samples were recorded at room temperature in transmission mode using ion chambers at beamline BL14W1 of the Shanghai Synchrotron Radiation Facility (SSRF), China. Catalysts Activity Tests. Catalytic Activity Tests in a Fixed-Bed Reactor. PtxNiy/C was studied as the SCR catalyst for NO removal with H2 in a fixed-bed reactor. PtxNiy/C catalysts (300 mg) were packed inside a tube, and the gaseous mixture (consisting of NO, H2, O2, and N2 with a total flow rate of 160 mL/min) passed through the catalysts. The reaction temperature was controlled in the range of 20− 300 °C by an intelligence temperature controller. Fabrication of Carbon Paper Loaded with PtxNiy/C. To load the PtxNiy/C catalysts on the carbon paper, 4 mL of isopropyl alcohol and 2 mL of deionized water were added into the vial containing the catalyst weighing 30 mg and then placed in an ultrasonic cleaner for 30 min. After that, the mixed liquor was spurt on carbon paper (size 5.5 cm × 5.5 cm) uniformly. Finally, the carbon paper was loaded in an oven to dry at 80 °C for 6 h. Figure 1 shows our gas diffusion reactor used for measuring the activity of the PtxNiy/C for the removal of NO. The prepared carbon paper, loaded with catalysts, was placed in the middle of flow field and cover board. Flow field ensures rapid provision to relatively uniform gaseous mixture flow distribution containing NO, H2, O2, and N2, and then NO and H2 were adsorbed by the catalysts for the subsequent occurrence of the oxidation−reduction reaction. The concentration of NO and NO2 was continually measured using a chemiluminescent NO-NO2-NOx analyzer (Thermo Scientific, Model 42i), which was connected directly to the reactor outlet. The conversion of NO was calculated using the following equation
on Pt/carbon black also proves that some electrons transfering from Pt to the carbon,18 specifically at the interface of Pt−C, can enhance the activity by tuning the electronic structure of Pt. Although many efforts are focused on choosing carries for Ptbased catalysts, there is less understanding of varying compositions influence on the H2−SCR performance. The bimetallic composition can offer several advantages over the Pt monocomposition: the synergetic effect between two elements, the change of the electronic structure, and the morphology effect can be obtained in order to enhance activity.19 In addition, this bialloy Pt with non-noble transition metals can reduce the precious Pt consumption by increasing the intrinsic activity. Now, based on previous studies, the binary Pt−M (Ni, Co) are commonly used as the catalysts for promoting oxygen reduction reaction (ORR) activity.20 To the best of our knowledge, there are still insufficient studies focusing on the employment of bimetallic Pt−M as a H2−SCR catalyst. Here, we demonstrate that the binary PtxNiy alloy nanoparticles are synthesized via a one-pot preparation method on carbon black (XC-72), displaying an outstanding NO conversion performance with H2 as reductant. The PtxNiy nanoparticles grown directly on the high surface area XC-72 substrate achieve high dispersion. Moreover, here the adopted one-pot strategy is quiet facile and without the usage of any bulky capping agents. We have discovered that the intrinsic activity of Pt can be improved by tuning its d-band structure by the inducement of Ni for the compositional change.
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EXPERIMENTAL SECTION
Preparation of PtxNiy Nanoparticles on Carbon Black (XC72). The PtxNiy/C catalysts are prepared by the solvothermal pathway using the N,N-dimethylformamide (DMF) as the solvent and reductant. First, 525 mg of carbon black (XC-72) is added into the 40 mL DMF solution and then magnetically stirred for 60 min at 60 °C under 450 rpm to form homogeneous ink. After that, a certain amount of chloroplatinic acid (H2PtCl6·6H2O) and Ni(NO3)2·6H2O is simultaneously added into the carbon black ink and magnetically stirred for 4 h at 60 °C. Later the mixture is transferred into the Teflon pressure vessel. The reactors are loaded in an oven to heat at 170 °C for 12 h before it is cooled to room temperature. Then, the mixture is washed several times during filtration, followed by retentate drying at 80 °C. Characterization of Catalyst. The crystal structure of catalysts was investigated using powder X-ray diffraction (XRD) using a D/
NO removal efficiency =
C NOin − C NOout C NOin
× 100% (1)
where CNOin and CNOout depict the NO inlet and outlet concentration of the reaction, respectively. B
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 2. (a) XRD patterns of Pt/C and PtxNiy/C catalysts. (b) Raman spectra of XC-72 and PtxNiy/C catalysts. (c) ID/IG intensity ratio of catalysts.
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RESULTS AND DISCUSSION Compositions, Morphology, and Structure of PtxNiy/C. We performed inductively coupled plasma mass spectrometry (ICP-AES) and energy-dispersive X-ray (EDX) spectra to determine the exact composition of the prepared PtxNiy/C samples. The EDX spectra clearly show the Pt−K and Ni-M peaks, and the total mass loading of PtxNiy is a range of 8%− 10%. The bulk mole ratio of Pt/Ni in our prepared different compositions cases is 82/18, 65/35, 58/42, 37/63, and 21/79, respectively, corresponding to Pt82Ni18, Pt65Ni35, Pt52Ni48, Pt37Ni63, and Pt21Ni79. Both of the Ni and Pt metals are the cubic closed-packed structure, and their space group belongs to Fm3m. Thus, binary alloy formation between Pt and Ni may occur in a wide range of compositions. The X-ray powder diffractions of different PtxNiy/C compositions (Figure 2b) show all of the prepared samples are the face-centered-cubic (FCC) phase. An interesting feature is that the (111) diffraction plane shifts from the close Pt position to the Ni(111) position with increasing Ni contents, that indicated the formation of the Pt−Ni alloy. It is clearly found that the peak width is quiet broad, which implies that the alloy particles are quite smaller in size. The average particle size of different PtxNiy samples mainly distributes in a range of 2−4 nm. Raman spectroscopy is useful tool to acquire information on structures in all kinds of carbon materials. As shown in Figure 2b, all prepared samples depict a D band located around 1350 cm−1 and a G band located around 1580 cm−1.21 For the socalled G band, it is primarily generated from the stretching vibration of the C−C bond, which is common to all sp2 carbon systems. This band is highly sensitive to strain effects in sp2 hybridization and can be used to probe any modification to the flat geometric structure, such as the strain induced by external force. As presented in Figure 2b, the PtxNiy/C shows a blueshift compared to pure XC-72. The D band results from the
disorder and the defects in graphite. The Id/Ig intensity ratio between the disorder-induced D band and the Raman allowed G band can be used to quantitatively describe the disorder phenomena.22 Figure 2c presents that the Id/Ig in all PtxNiy/C samples is higher than XC-72, and the Pt65Ni35 gives the highest D band intensity. The variations in Raman properties of prepared PtxNiy/C are mainly due to the DMF and grown PtxNiy particles causing graphitic expansion and inducing more disorderliness. Apart from the difference of the crystal structure in different PtxNiy alloys, their morphology is an additional factor of concern. Figure 3 is the performed transition electron microscopy (TEM) images of different PtxNiy compositions. The even distribution of the PtxNiy particles on the carbon support is clearly observed. The insert high-resolution TEM (HRTEM) images indicated the corresponding d-space of the (111) plane gradually decreases with more Ni contents from 8%Pt/C of d111 = 0.23 nm to Pt21Ni79 possessing d111 = 0.21 nm. It means that the lattice parameter of the PtxNiy alloy lies in between FCC Pt and FCC Ni. Those observations are consistent with the XRD revelations. The histograms reveal that the particle size distribution is in the range of 2−8 nm and mainly concentrated on 3−4 nm. Previous studies found that the Pt−Ni alloy can transform into an octahedral shape on addition of some structure-directing agents such as benzoic acid, polyvinylpyrrolidone, et al.20 Here, the PtxNiy nanoparticles acquire no specific shape, mainly due to no usage of the surfactants. Additionally, this one-pot preparation via direct growth on carbon support inhibits the octahedral formation to a certain extent. The performed nitrogen adsorption isotherm BET reveals the surface area of PtxNiy/C in the range of 201− 220 m2 g−1, showing no dependency upon the composition. However, an interesting feature is that the surface area of pure XC-72 support is smaller than the prepared PtxNiy/C, which C
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 3. TEM and HRTEM images of PtxNiy/C catalysts: (a) Pt/C, (b) Pt82Ni18/C, (c) Pt65Ni35/C, (d) Pt58Ni42/C, (e) Pt37Ni63/C, (f) Pt21Ni79/ C.
means that the DMF as a solvent expands graphite resulting in an increase of the XC-72 surface area, and this is verified by performed Raman spectra. The higher surface area favors enhancement in de-NO performance. Catalysts Activity. NO Reduction on PtxNiy/C Catalysts by H2−SCR in a Fixed-Bed Reactor. To characterize the NO reduction performance of the catalysts, a fixed-bed reactor was first employed. The removal activity of NO with H2−SCR over different PtxNiy/C catalysts was shown in Figure 4, the feed stream including 1,000 ppm of NO, 15,000 ppm of H2, and 2% O2 for a GHSV of 34,000 h−1. As illustrated in Figure 4, almost all of the catalysts could maintain a stable NO removal ratio in a wide temperature window of 100−300 °C; notably for the Pt65Ni35 case, it even obtains nearly 70% removal at 60 °C. In comparison to other low-temperature catalysts such as Pt/ MgO-CeO2 (more than 140 °C),11 NiCo2O4 (more than 75% at 150 °C),23 et al., the prepared catalyst in our quest exhibits a highly attractive performance. The Pt based catalysts for SCR are often susceptible to the oxygen and exhibit a classical volcano shape due to the combustion reaction between oxygen and hydrogen. While for all prepared PtxNiy catalysts, this volcano shape is inhibited in different contexts. Note that this removal tendency is distinct from a pure Pt/C catalyst exhibiting an obvious volcano shape, that insinuates the Ni species in this bimetallic alloy in cooperation with H2 show
Figure 4. NO removal by different PtxNiy/C catalysts in a fixed-bed reactor.
reaction preference for NO over oxygen. For low level Ni content Pt82Ni18 has a weak volcano shape; this is mainly due to the fact that Ni content is quite low. In contradiction, Pt21Ni79 exhibits an interesting feature of rise in removal tendency to the corresponding temperature elevation, but in the case of Pt37Ni63 still a weak volcano shape prevails. It indicates that the NO conversion was dependent upon the composition of Pt and Ni D
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surface or the surface atomic layers mainly comprised of the Pt phase for the low Ni content samples. It is also confirmed by Ni-2p XPS as depicted in Figure 6b that the Ni-2p peaks are so weak that they are hard to observe in low Ni content samples but can be observed in the Ni phase in Pt37Ni63/C and Pt21Ni79/C, possessing higher Ni contents. It is mainly due to the fact that the Ni(NO3)2 precursor more readily reduces in DMF solvent leading to the formation of Ni metal nucleus at first, and then the growth of the Pt phase occurs on this Ni particle surface, eventually resulting in the formation of an outstanding structure. For the more Ni contents cases, the Ni atoms and Pt atoms are both detected in the XPS which means that Pt and Ni form the alloy phase. In this circumstance, the electronic structure and valence state of the Pt phase are affected significantly. In the Pt21Ni79/C case, we even observe the Pt0 state, and the Pt valence states are quite complex compared to other cases. According to the XPS information, we attempt to draw their surface layer structure as shown in Figure 6. NO Reduction on PtxNiy/C Catalysts in a Gas Diffusion Reactor. Although the PtxNiy/C catalysts showed a good performance by removing NO in a fix-bed reactor, more interesting results are generated in further research by using a gas diffusion reactor (as shown in Figure 1), as in our previous report,18 for NO removal. The reactant gas consisted of 1,000 ppm of NO, 1% H2, and 2% O2 with N2 as the balance gas. The total flow rate was 120 mL/min, resulting in a very short residence time of 0.09 s. The reaction temperature ranged from 20 to 90 °C. From Figure 7a, it could be seen clearly that all the PtxNiy/C catalysts exhibited excellent performance under set experimental conditions. Pt65Ni35/C showed the best performance, which was the same as before (Figure 4); NO removal reached almost 100% only at 60 °C. To the best of our knowledge, there have been fewer reports (Machida et al.26 found that NOx conversion can reach to 89% at 90 °C over 1 wt % Pt/ TiO2−ZrO2) that could elucidate acquiring of high catalytic activity in H2−SCR at such a low temperature. Rational variation of Pt and Ni contents in catalysts results in distinct catalytic performance, removal of the entire NO in the mixed gas (100%) at the different corresponding values of temperature scale (as shown in Figure 7b). Even for Pt21Ni79/C catalysts (NO removal reached about 100% when the temperature was 95 °C), performance in terms of temperature lowering is far better than other reports. It can be attributed to the even distribution of the gas in the flow field, high surface area of XC-72 support, and high catalytic activity of PtxNiy/C. Effect of SO 2 in the Reaction Feed Stream. The antipoisonous property of catalysts is important for potential applications. Therefore, the effect of SO2 on the performance of Pt65Ni35/C catalysts was also investigated. About 62 and 105 ppm of SO2 was introduced into the feed stream, consisting of 1,000 ppm of NO, 0.5% H2 and 2% O2 (N2 balance), respectively. Li et al.27 found that 50 ppm of SO2 caused serious deactivation (NO conversion decrease from 90% to 30%) over Pt/Ti-MCM-41, and the deactivation was reversible. Qi et al.28 have also reported a similar result over Pd/Ti-PILC catalysts. From Figure 8, it was found that a significant degradation in NO conversion (reduced from almost 100% to about 20%) was obtained over the Pt65Ni35/C catalysts, after being under the slight influence of SO2 concentration. However, the subsequent removal of SO2 resulted in complete restoration of the catalytic activity to the initial level. The influence of SO2 was completely
in the catalysts, implying that variation in Ni contents may lead to the arousal of different structures to be contemplated as responsible for the extent of NO removal. In addition, Pt21Ni79/C also showed an efficient NO removal (more than 90%) in the temperature range of 120−300 °C. It was worth noting that the relationship between NO conversion and the Pt content was nonlinear; NO conversion could only reach about 70% in the entire temperature range of 120−300 °C for Pt82Ni18/C, having the highest Pt content. These results coincided with the XPS analysis. In order to evaluate more accurately the Pt activity for all the prepared PtxNiy/C catalysts, the NO conversion (at 120 °C) of per unit mass of Pt for each PtxNiy/C catalyst has been calculated. Here, we used a normalization method to compare the activity for each catalyst, and the activity of Pt/C was used as the benchmark; Figure 5 depicts their activity. We can find
Figure 5. Activity of per unit Pt for each catalyst.
that all the Ni doped cases have higher activity than pure Pt/C, and the activity of unit Pt increases to the corresponding enhancement of Ni composition. Pt21Ni79/C has the highest activity of 2.5 times than Pt/C, confirming that Ni as dopant can efficiently promote Pt activity, especially in the case of alloy formation. It suggests that the electronic structure of Pt can be effectively modified by Ni resulting in the improvement of catalytic activity toward NO removal. Indeed, the role of surface Ni phase may play a synergistic effect. Additionally, this PtxNiy alloy can dramatically reduce the precious Pt consumption, making it economically attractive. To understand the NO removal differences over PtxNiy/C catalysts, the X-ray photoelectron spectroscopy (XPS) was performed to investigate the surface composition and electronic structure of the catalysts. As shown in Figure 6a (Pt-4f XPS), a remarkable feature is that, for all the prepared PtxNiy/C materials, the binding energies of Pt 4f7/2 and Pt 4f5/2 peaks appear at 71.58 and 74.96 eV, respectively, which are slightly higher than metal Pt24 (4f7/2 ∼ 71.2 eV, 4f5/2 ∼ 74.4 eV) and is consistent with our previous finding. This rise in Pt-4f binding energy can be attributed to the transference of some electrons from Pt to Ni or carbon.25 Additionally, a very interesting feature appears in the disappearance of the Pt-4f7/2 peak near primary in the Ni-3s core level XPS around 68 eV for all the low Ni contents cases such as Pt82Ni18, Pt65Ni35, and Pt52Ni48. It is worth mentioning that XPS is the only surface analysis technique which provides surface atomic layer structure. Thus, it implies that there is no Ni residing in the layers near to the E
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 6. (a) XPS spectra of Pt-4f in PtxNiy/C compositions. (b) XPS spectra of Ni-2p in PtxNiy/C compositions.
Figure 7. (a) NO removal by different PtxNiy/C catalysts in a gas diffusion reactor. (b) The corresponding temperature of 100% NO removal for each catalyst.
decreased from 1% to 0.5%, and the removal efficiency of NO still reached 100% by increasing the reaction temperature from 60 to 80 °C.
faded, meaning that the poisonous effect and restoration were due to reversible coverage of the Pt side by adsorbed SO2, so the structure of the catalysts surface did not acquire any irreversible change by SO2. Additionally, the phenomena implied that introducing Ni to modify Pt was good for enhancing the SO2 tolerance as well, possibly due to a weaker bonding between the SO2 and PtNi. Furthermore, it is important to note that, in comparison to earlier experiments (Figure 7), even the concentration of H2 in the mixed gas was
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CONCLUSIONS The experimental work in this study infers that we have synthesized different binary PtxNiy/C alloy nanoparticles catalysts via a new one-pot method. The direct growth of PtxNiy nanoparticles on the XC-72 carbon support enables F
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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AUTHOR INFORMATION
Corresponding Author
*Phone: +86-21-64251668. Fax: +86-21-64251668. E-mail:
[email protected]. ORCID
Wei Sun: 0000-0001-5032-0094 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research is based on work supported by the National Natural Science Foundation of China (21277045).
Figure 8. Effect of SO2 concentration on NO removal over Pt65Ni35/ C.
REFERENCES
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acquisition of high surface area and uniform distribution on the carbon surface. Further XPS and Raman data prove that adding Ni element into Pt can change the electronic structure and the morphology of these two elements, and these changes eventually result in the emergence of a synergetic effect between these two elements. These change may be the main reason for the attractive performance of the PtxNiy/C catalysts. On the other hand, adding Ni can reduce the precious Pt consumption, subsequently reducing the operational costs. The prepared PtxNiy/C catalysts were employed as H2−SCR catalysts for NO removal in two different reactors. Our study indicated that PtxNiy/C catalysts exhibited a high low temperature activity in the fixed-bed reactor, and all the catalysts maintained a stable NO conversion at a wide temperature window, wherein maximum NO conversion (more than 95%) was obtained from 100 to 300 °C over the Pt65Ni35/C catalyst. However, calculating the NO conversion of per unit mass of Pt for each catalyst and using a normalization method to compare their performance, Pt21Ni79/C exhibited the best catalytic performance. PtxNiy/C catalysts also exhibited an attractive performance when they were introduced for NO removal in our new gas diffusion reactor. NO conversion reached 100% over all the catalysts when the temperature was below 95 °C, and Pt65Ni35/ C exhibited the best performance (at 60 °C). Finally, the effect of SO2 on the Pt65Ni35/C was investigated at 80 °C. The result indicated that although the PtNi/C catalyst lost its catalytic activity when SO2 was added into the mixed gas, it recovered rapidly to the initial catalytic level after its removal. The striking results for the two different reactors could be attributed to the following two reasons: one is the different working parameters, but another more important reason is that the gas diffusion reactor has many advantages compared with a fixed-bed reactor. Flow field proved a zigzag gas passage for the mixed gas which brings a better distribution of gases and a longer residence time. On the other hand, carbon paper also increases the contact of mixed gas with catalysts. The analysis has been added in the manuscript in the conclusion part. All of the above results suggest that the electronic structure modulation of Pt obtained via addition of Ni element enhanced the catalytic activity, and all prepared binary PtxNiy/C catalysts exhibited good performance in the H2−SCR reactor. Additionally, our new reactor can be considered as a good choice for NO removal in our future studies. G
DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
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DOI: 10.1021/acssuschemeng.7b00540 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
