Catalytic combustion of toluene over cobalt oxides supported on

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Materials and Interfaces

Catalytic combustion of toluene over cobalt oxides supported on graphitic carbon nitride (CoOx/g-C3N4) catalyst Dongmou Luo, Shusen Liu, Junjie Liu, Jinxian Zhao, Chao Miao, and Jun Ren Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02625 • Publication Date (Web): 16 Aug 2018 Downloaded from http://pubs.acs.org on August 17, 2018

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Industrial & Engineering Chemistry Research

Catalytic combustion of toluene over cobalt oxides supported on graphitic carbon nitride (CoOx/g-C3N4) catalyst Dongmou Luo a, Shusen Liu a, b, Junjie Liu c, Jinxian Zhao a, Chao Miao a, Jun Ren a* a

Key Laboratory of Coal Science and Technology (Taiyuan University of Technology),

Ministry of Education and Shanxi Province, No. 79 Yingze West Street, Taiyuan 030024, China b

Lignite Fly Ash Institute of Engineering & Technology, Xilingol Vocational College,

Inner Mongolia, Xilinhot 026000, China c

Division of Nanoscale Measurement and Advanced Materials, National Institute of

Metrology, No. 18, Bei San Huan Dong Lu, Chaoyang Dist, Beijing 100029, China *Corresponding author. Mailing address for correspondence: No. 79 Yingze West Street, Taiyuan 030024, China. Tel/Fax: +86 351 6018598. E-mail address: [email protected] (J. Ren). Abstract: Graphitic carbon nitride (g-C3N4) supported CoOx catalysts were prepared by impregnation method and comprehensively characterized by XRD, N2 physisorption, TEM, H2-TPR, and XPS. The catalytic performance tested by catalytic combustion of toluene indicate that 10% CoOx/g-C3N4 catalyst exhibits the highest activity, achieving a toluene conversion of 90% at a temperature of approximately 279 °C, compared with other CoOx catalysts that supported on SBA-15, γ-Al2O3 and activated carbon (AC). The specific structure of g-C3N4 made it a N and electron-rich material, which might be the reason for the existence of Co3O4 active phase, high surface Co3+ content and high density of surface oxygen adsorption species, and the facile 1

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

reducibility of Co3+. Moreover, no significant decrease in catalytic efficiency is observed over different temperature stages on the 10% CoOx/g-C3N4 sample, which indicates that the catalyst’s stability is excellent under the conditions required for toluene combustion. Keywords: graphitic carbon nitride, CoOx/g-C3N4 catalyst, catalytic combustion, toluene 1. Introduction Volatile organic compounds (VOCs) are already becoming as one of the major environmental pollutants, for their harm to the environment and human health. At present, manifold applicable technologies, such as thermal combustion, catalytic combustion, adsorptive recovery, absorption, and biofiltration have been widely employed to remove VOCs.1, 2 Among all of these techniques, catalytic combustion has been recognized as the most effective one for its energetic efficiency, strong handling ability, and no secondary pollution. The study of the catalytic combustion of VOCs focuses on the search for a catalyst characterized by high activity and stability. Supported noble metals including Pt, Au, Pd, and Rh are reported to be efficiency to VOCs combustion,3-6 VOCs could be removed on this kind of catalyst at low temperature. However, high costs and easy deactivation of noble metal catalysts limit their application. Great efforts have been made to develop non-noble metal catalysts for the catalytic combustion of VOCs, such as MnO2, Co3O4, NiO, Fe2O3, Cr2O3, CuO, and CeO2.7-9 Among the most studied metal oxides, it was proved that Co3O4 have shown 2


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to be efficient in the complete oxidation of VOCs at low temperatures.10, 11 The high activity of this oxide is due to its excellent reducibility, high content of oxygen vacancies, and high concentration of electrophilic oxide species (Oads, O- or O2-)12, which are the primary factors affecting the oxidation of VOCs. As we all know, the catalytic performance of metal oxides could be improved if they are deposited on a support rather than used in bulk. This is due to the fact that the supports greatly influence the final properties of the catalyst that determine its oxidation activity,13-15 such as texture, surface acidity and basicity, thermal stability, and electrical conductivity. Therefore, different supports such as Al2O3, ZrO2, TiO2, SiO2, ZMS-5, and CeO213,

16-19

have been used in the catalyst development. For

example, Song et al.14 synthesized carbon nanotubes supported Co3O4 (Co3O4/CNTs), and found that the defects of CNTs could significantly influence the catalytic activity of Co3O4/CNTs in catalytic combustion of toluene reaction. Gutiérrez-Ortiz et al.20 prepared MnOx/HZSM-5 catalyst, and found that the acidic properties of HZSM-5 lead to a high dispersion of MnOx, which made MnOx/ZSM-5 an efficient catalyst for catalytic oxidation of dichloromethane and trichloroethylene. Lin et al.21 also found that the mesoporous CoOx/mSiO2 exhibits superior activity in toluene oxidation compared to hollow CoOx/hSiO2. In recent years, graphitic carbon nitride (g-C3N4), an excellent catalyst support with high thermal stability, rich surface chemistry and many other attractive properties, has been widely studied for its application in heterogeneous catalysis.22-24 Due to its unique structure, g-C3N4 facilitates electron transfer in the supported catalysts, which 3



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greatly improve the stability of highly dispersed metal particles. In addition, g-C3N4 contains a large number of nitrogen atoms, as its network is mainly composed of tertiary and aromatic amines,25 which also contribute to the stability of the metal particles by creating a tight coordination. Furthermore, the richness of sp2 (C-N) hybridized bond in g-C3N4 structure made it good thermal and chemical stabilitys.26 Muniandy et al.27 reported that copper-modified graphitic carbon nitride nanosheets (Cu-g-C3N4) have good catalytic activity towards liquid phase selective oxidation of benzene and various VOCs. Huang et al.28 synthesized Cu2O/g-C3N4 catalysts and tested them in the catalytic oxidation of CO, obtaining its complete conversion at relatively low temperatures. Lin et al.25 prepared Co-N-C supported g-C3N4 catalyst for the catalytic oxidation of ethylbenzene, and found the activity was mainly resulted from the Co-Nx active site and the synergistic effect between Co-N-C and g-C3N4. From the above results, it can be concluded that g-C3N4 can act as an excellent support for metal oxides in catalytic oxidation reactions. In this work, g-C3N4 was synthesized by a conventional thermal polymerization method and used as support for the preparation of CoOx/g-C3N4 catalysts following a simple impregnation procedure. Catalytic combustion of toluene was chosen as the model reaction for the evaluation of catalytic performance. X-ray diffraction (XRD), N2

physisorption,

transmission

electron

microscopy

(TEM),

hydrogen

temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the catalysts of the physicochemical properties in order to study the relationship between those properties and the catalytic 4


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performance. 2. Experimental 2.1. Materials Guanidine hydrochloride, cobalt nitrate (Co(NO3)2•6H2O), and toluene were received by Aladdin Chemical Regent Co. Ltd. (Shanghai, China), GuangFu Chemical Regent Co. Ltd. (Tianjin, China), and ShenTai Chemical Regent Co. Ltd. (Tianjin, China) respectively. Commercial γ-Al2O3, SBA-15, and activated carbon (AC) were purchased from the Institute of Coal Chemistry Chinese Academy of Sciences. Deionized water obtained from a Milli-Q system (Millipore, Bedford, MA, USA). H2 (>99.99%), Ar (>99.99%), and synthetic air (20 vol% O2 and 80 vol% N2) were purchased from the Taiyuan Iron and Steel Company (China). 2.2. Catalyst Preparation Guanidine hydrochloride was used as the precursor, and g-C3N4 was synthesized via a facile method. In detail, the guanidine hydrochloride powder was placed into a crucible with a cover and heated to 550 °C with a heating rate of 3 °C/min in a muffle furnace, and the sample was then kept at 550 °C for 4 h. The resulting yellow powder was collected for use without further treatment. The certain stoichiometric amount of Co(NO3)2•6H2O were dissolved in distilled water (3 mL), and g-C3N4 (0.5 g) was dispersed in the solution, the mixture was ultrasonic for 60 min at room temperature. The solvent was then removed by evaporation at 120 °C for 2 h. The resulting solid mixture was placed into a crucible with a cover, heated to 400 °C at a heating rate of 5 °C/min, and kept for 2 h in a 5



muffle furnace. After that, the sample was naturally cooled down to room temperature. At the end of this procedure, the catalysts with different mass ratio were obtained. For comparison, CoOx catalysts supported on commercial SBA-15, γ-Al2O3, and AC were also prepared by the same procedure. 2.3. Catalyst characterizations Powder XRD patterns were collected using a Rigaku D/Max 2500 system equipped with a Cu Kα source (λ=1.54056 Å) operated at 40 kV and 100 mA in the 2θ range of 5-85 ° with a step size of 0.05 °. The texture properties were characterized by N2 adsorption-desorption at -196 °C on a Micromeritics 3H-2000PS2 (BeiShiDeInstruments S&T. Co., Ltd, Beijing, China). Before the measurement, the sample was heated to 200 °C under vacuum condition, and degassed for 3 h. Brunauer-Emmett-Teller (BET) equation was used to calculate the specific surface area of the sample based on the linear part of BET plot at the p/po range of 0.05 to 0.25, the pore volume and pore size distribution were estimated from the desorption branch of N2 isotherms by the Barret-Joyner-Halenda (BJH) method. The H2-TPR measurements of the samples were carried out a Finesorb 3010 (Finete, China) analyzer, equipped with a thermal conductibility (TCD) detector. The measurements were carried out on a 30 mg sample, placed in a U-shaped quartz tube. Firstly, the sample was heated to 100 °C, and kept at 100 °C for 60 min in flowing Ar (40 mL/min) to remove H2O and other volatile gases. After that, the sample was cooled to room temperature, the gas was converted to H2/Ar (10 vol%) at a flow rate 6


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of 40 mL/min. Then, the temperature was increased to 800 °C with a heating rate of 5 °C/min. TEM photos were taken on a JEM-2010F (JEOL, Japan) transmission electron microscope at 100 kV. The support or catalyst sample was introduced into absolute ethyl alcohol, and treated with ultrasonic for an adequate dispersion. And, the TEM sample was made by dripping the mixture onto a copper grid (400 meshes) coated with a carbon film. X-ray photoelectron spectra (XPS) was carried out on a Thermo ESCALAB 250 spectrometer with an Al Kα X-ray source. 2.4 Catalytic activity measurements The catalytic combustion of toluene was performed on a fixed-bed reactor, Typically, 50 mg of the catalyst was diluted with 1 g quartz sands (40-70 mesh) to minimize the effect of hot spots, the mixture was packed in the middle of a tubular micro-reactor. A K-type thermocouple was used to measure the real temperature of the catalyst bed by locating above the catalyst (no contact). Toluene (1000 ppm) which was diluted with synthetic air (20% O2+80% N2) with a total flow rate of 130 mL min-1, was passed through the catalyst bed, giving a gas hourly space velocity (GHSV) of ca. 10000 h-1. After a 10 min flow-stable, the reactor was heated to 100 °C and maintained at this temperature for 90 min to avoid the overestimation of toluene conversion caused by its adsorption on the catalyst. The temperature of reactor was then heated to 400 °C with a rate of 5 °C/min to obtain the light-off curve. The toluene conversions were obtained under each temperature after 24 min of 7



stabilization. The gas mixture after reaction was separated with a SE-30 column for organic gases and a Carboxen 1000 column for permanent gases, and quantitatived by Gas Chromatograph (Haixin GC-950) equipped with a FID and a TCD. The carbon balance in each reaction was reckoned to be 100% ± 5%, which indicates that CO2 was the only carbon-containing product. Thus, the product selectivity will not be discussed in the present work. The conversion(X%) of toluene into CO2 were calculated based on the following equations: ܺ%=

ሾC7 H8 ሿin - ሾC7 H8 ሿout ×100% ሾC7 H8ሿin

Where [C7H8]in and [C7H8]out represent the toluene concentrations in the inlet and outlet currents, respectively. In what follows, T10, T50, and T90 denote the reaction temperatures at which toluene conversions of 10%, 50%, and 90% were achieved, and are used to express as a standard for comparing the catalytic activity of the tested formulations. 3. Results and discussion 3.1. XRD characterization

(a)

• g-C3N4

•

♦

•

♦ Co3O4

♦

♦

♦

♦

20%CoOx/g-C3N4 ♦ ♦ 15%CoOx/g-C3N4

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10%CoOx/g-C3N4 5%CoOx/g-C3N4

g-C3N4 10

20

30

40

50

60

2-Theta(degree) 8


70

80

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(b)

g-C3N4 ♦ Co3O4 ♦

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


♦

♦

SiO2

♦

γ-Al2O3

AC

10% CoOx/g-C3N4 ♦ ♦♦

10% CoOx/SBA-15

10% CoOx/γ-Al2O3

10% CoOx/AC 10

20

30

40 50 60 2-Theta(degree)

70

80

Figure 1. XRD patterns of (a) g-C3N4 and CoOx/g-C3N4 catalysts and (b) g-C3N4, SBA-15, γ-Al2O3 and AC supported CoOx catalysts. Figure 1(a) depicts the typical XRD patterns of g-C3N4 and CoOx/g-C3N4 catalysts. In the case of g-C3N4, the peaks at 13.1 ° and 27.5 ° show that the g-C3N4 structure has been successfully obtained, as the two peaks are attributed to (100) and (002) plane (JCPDS 87-1526).29, 30 The characteristic diffraction peaks of g-C3N4 are shown, for reference, in the spectra of all the CoOx/g-C3N4 samples. Besides the (002) and (100) diffraction peaks, other peaks of the samples can be indexed as cubic Co3O4 with Fd-3m space group. More specifically, the peaks at 2θ values of 18.90 °, 31.29 °, 36.81 °, 38.54 °, 44.80 °, 59.37 °, and 65.27 ° correspond to the (111), (220), (311), (222), (400), (511), and (440) planes, respectively31(JCPDS 42-1467). In addition, the crystallinity of Co3O4 phase in CoOx/g-C3N4 was gradually increased with the Co mass ratio in the initial precursors. Meanwhile, the diffraction peaks at 13.1 ° and 27.5 ° that belonging to (100) and (002) planes of g-C3N4 become noticeably weaker and broader. The results indicate that the stacking structure of g-C3N4 was partly 9



broken, which may be caused by the intercalation of Co3O4 nanoparticles, thus the g-C3N4 layer becomes thinner.32 It should be noted that the characteristic peaks of Co3O4 can easily be identified in the XRD patterns of 10% CoOx/SBA-15, 10% CoOx/γ-Al2O3, and 10% CoOx/AC, shown in Figure 1(b). However, they are weaker for catalysts supported on SBA-15, γ-Al2O3, and AC compared to those supported on g-C3N4 due to their different textural properties. 3.2. N2 physisorption analysis N2 adsorption-desorption isotherms and pore size distributions of the g-C3N4 support and of the supported CoOx catalysts are presented in Figure S1(a-h). The specific surface areas, pore volumes and pore size are listed in Table 1. As shown in Figure S1(a-e), the g-C3N4 and CoOx/g-C3N4 catalysts exhibited a type IV isotherm with a type H3 hysteresis loops at a relative pressure of 0-1.0, which reveals that the samples were mesoporous materials. The hysteresis loop of g-C3N4 begins at the relative pressure of ca. p/po =0.4 and shifts to higher p/po values for increasing mass ratios of CoOx, indicating that changes in the textural properties are occurring. As confirmed by Table 1, g-C3N4 shows a small specific surface area, and a large and broad pore size distribution, due to the empty spaces between particles, centered at ca. 21.8 nm. Compared with g-C3N4, the specific surface area, total pore volume, and pore size of CoOx/g-C3N4, increase gradually with the increase of cobalt species mass ratio, with the exception of the 20% CoOx/g-C3N4 sample. This is due to the formation of CoOx nanoparticles among the interlayers of g-C3N4, which induces the formation of mesoporous structures.33 The same conclusion had been drawn from the 10


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analysis of the XRD results. In addition, high specific surface area was obtained for the 10% CoOx/SBA-15, 10% CoOx/γ-Al2O3, and 10% CoOx/AC catalysts, and their mesopore volumes were much higher than those of g-C3N4 supported catalysts, which were due to the excellent texture properties of the SBA-15, γ-Al2O3, and AC supports. It is worth noting that the 10% CoOx/SBA-15 sample has the highest specific surface area and pore volume among all the catalysts tested. Generally, catalysts with large surface area are expected to exhibit better catalytic performance due to their capability of accommodating a larger number of active sites.34 In the present case, the activity of the catalysts is not exactly correlated to the surface area, indicating that it is not the critical factor influencing the performance of the catalysts. Table 1 Textural properties of g-C3N4 and supported CoOx catalysts SBETa

Vtotalb

Dp c

(m2 g-1)

(cm3 g-1)

(nm)

g-C3N4

16.83

0.16

21.8

5% CoOx/g-C3N4

31.94

0.26

22.6

10% CoOx/g-C3N4

46.99

0.37

24.4

15% CoOx/g-C3N4

49.92

0.44

24.1

20% CoOx/g-C3N4

46.48

0.41

24.5

10% CoOx/SBA-15

460.90

0.84

5.5

10% CoOx/γ-Al2O3

138.72

0.67

13.4

10% CoOx/AC

419.58

0.44

4.8

Samples

a

Surface area obtained by using BET method.

b

Total pore volumes estimated from the N2 adsorption isotherms at p/po = 0.99

c

The average pore size of the catalysts calculated from the N2 desorption branches using the BJH

method

11



3.3 TEM analysis

Figure 2. TEM images of different supported CoOx catalysts. TEM photos and particle distribution of 10% CoOx/g-C3N4, 10% CoOx/SBA-15, 10% CoOx/γ-Al2O3, and 10% CoOx/AC catalysts are presented in Figure 2(a-h). For 12


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10% CoOx/g-C3N4, the dark Co3O4 phase is distributed on the g-C3N4 layer. Figure 2(b) clearly shows the existence of Co3O4 in the sample. The high resolution (HR)-TEM images show that the lattice spacings in the sample are 0.243 nm and 0.466 nm, which can be assigned to the (311) and (111) planes of Co3O4, respectively. On the other hand, the TEM images of the CoOx catalysts supported on SBA-15, γ-Al2O3, and AC, reported in Figure 2 (d, f, h), only show the (111) planes of Co3O4. It can be seen that CoOx particles are more homogeneously dispersed on the g-C3N4 surface than on the other three supports. The role of g-C3N4 as a support is probably to enhance the dispersion of CoOx particles on the surface of g-C3N4 as the presence of a large number of free -NH2, -NH groups helps to anchor the CoOx particles, thereby enhancing metal particle dispersion.35 It can be also deduced qualitatively that the crystallite size of CoOx in different catalysts followed the order 10% CoOx/g-C3N4 > 10% CoOx/SBA-15 > 10% CoOx/AC > 10% CoOx/γ-Al2O3, which is consistent with the XRD results. 3.4 H2-TPR analysis 10% CoOx/g-C3N4

(a) 248

10% CoOx/SBA-15

TCD Signal (a.u.) -x10 -x10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


260

10% CoOx/γ-Al2O3 260

10% CoOx/AC 342 100

200

300

400 500 600 o Temperature( C) 13


700

800


(b) 10% CoOx/g-C3N4 248 10% CoOx/SBA-15

260

10% CoOx/γ-Al2O3

260

-x10

-x10

TCD Signal (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10% CoOx/AC 342 150

200

250 o Temperature( C)

300

350

Figure 3. (a) H2-TPR profiles of different supported CoOx catalytsts; (b) H2-TPR partially magnified profiles of different supported CoOx catalysts. H2-TPR was used to test the reducibility of supported CoOx, the obtained TPR profiles and reduction peaks of all supported CoOx catalysts are presented in Figure 3(a) and Table S1, respectively. It can be observed that the 10% CoOx/g-C3N4 catalyst presented complex reduction peaks in the 200-550 °C temperature range. The first two peaks was attributed to the reduction of Co3O4 into CoO and CoO into metal Co. The different reduction peaks between 350 and 450 °C can be attributed to the reduction of CoO particles with different sizes, which interaction with the support.36, 37

The interaction may also be strengthened by the existence of the nitrogen atoms in

the g-C3N4 structure which can bring about strong interaction between CoOx species with g-C3N4.25 As shown in Figure S2, g-C3N4 exhibits a distinguishable peak at around 700 °C, which might be ascribed to the thermal vaporization or decomposition of g-C3N4.38 Due to the formation of CoOx nanoparticles among the interlayers of g-C3N4, the support’s structure is destroyed, potentially causing a shift in the 14


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decomposition temperature of g-C3N4. Thus, the peak at 509 °C may be attributed to the decomposition of g-C3N4. In addition, it should be noted that, the ordinates of the SBA-15 and γ-Al2O3 supported CoOx catalysts were amplified by 10 times than the original in order to clearly find the position of peak as shown in Figure 3. Among the CoOx catalysts supported on SBA-15, γ-Al2O3, and AC with the same loading, the 10% CoOx/SBA-15 catalyst shows three major reduction peaks centered at 260, 390, and 567 °C. According to the reported recognition,39, 40 the peak at around 260 °C can be attributed to the reduction of Co3+ to Co2+, while the peak at around 390 °C is associated with the reduction of Co2+ to Co0. And, the broad peak between 500 °C to 700 °C can be attributed to the reduction of the Co2+ which has strong interaction with the support, like the highly dispersed tetrahedral coordinated Co2+-silicate-like species. For 10% CoOx/γ-Al2O3 sample, three main reduction peaks centered at 260, 445, and 518 °C can be clearly observed, we suggest that the first and second groups are associated with the stepwise reduction of agglomerated Co3O4 to CoO and then to metallic Co. The broad signal at higher temperature (500-700 °C) may be caused by the total reduction of the CoAl2O4 or Co2AlO4, which were formed as the consequence of the strong metal-support interaction.41 The H2 consumptions at 342 and 401 °C of 10% CoOx/AC were associated with the reductions of Co3O4 to CoO, and CoO to Co. It can be clearly seen from Figure 3(b) that the 10% CoOx/g-C3N4 catalyst has a relatively lower reduction temperature of Co3+ compared to the other supported catalysts, which is a crucial factor in the advancement of the catalytic 15



combustion reaction.42, 43 This indicated that the N-containing sample could promote the reduction of neighboring Co ions and is characterized by a higher reducibility and oxygen mobility.44 3.5 XPS analysis 10% CoOx/g-C3N4

Co2p

10% CoOx/SBA-15

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10% CoOx/γ-Al2O3

10% CoOx/AC

810

800 790 780 Binding energy(eV)

770

Figure 4. Co 2p XPS spectra of different supported CoOx catalysts

16


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Figure 5. O 1s XPS spectra of different supports and the corresponding supported CoOx catalysts XPS spectra of different supported CoOx catalysts and supports are displayed in Figure 4 and Figure 5. For 10% CoOx/g-C3N4, it is clear that the C, N, O, and Co signals are visible in the full survey spectra (Figure S3(a)). The C1s XPS spectra of the sample is shown in Figure S3(b). The peaks of the sample at 284.1, 285.5, and 287.3 eV correspond to the C=C, C=N, and C-N bonds, respectively.25, 45, 46 Figure S3(c) shows the N1s XPS spectra of the sample, clearly, it could be deconvoluted into three peaks with binding energy of 397.8, 399.1 and 400.0 eV, indexed as pyridinic N (C-N-C), pyrrolic N(N-[C]3), and graphitic N(C-NH), respectively.30,

47

Figure 4

shows the Co 2p signals for the supported CoOx catalysts, all the Co 2p spectra 17



present two main peaks located at 794.8-797.5 and 779.6-781.2 eV, which can be ascribed to the Co 2p1/2 and Co 2p3/2 spin-orbitals, respectively.48 The Co 2p3/2 signal of each sample can be further divided into two parts, one at 779.3-779.8 eV and the other at 782.1-782.4 eV, ascribable to Co(III) and Co(II),49 respectively. Quantitative analyses indicate that the proportion of Co(III)/Co(II) follows the order 10% CoOx/g-C3N4 > 10% CoOx/SBA-15 > 10% CoOx/γ-Al2O3 > 10% CoOx/AC (Table 2), indicating that there were higher amounts of oxygen vacancies in the first catalysts more than in the last ones.50 That is, 10% CoOx/g-C3N4 possessed a higher surface oxygen vacancy density compared to the 10% CoOx/SBA-15, 10% CoOx/γ-Al2O3, and 10% CoOx/AC samples. This finding was further confirmed by the O 1s XPS spectra, as shown in Figure 5. In all cases, the supported CoOx catalysts showed two peaks located at 529.6-532.5 eV and 530.8-533.9 eV , corresponding to the surface lattice oxygen (Olatt) and adsorbed oxygen (Oads) species,49 such as O-, O2-, and O22-, respectively. As for the SBA-15 and γ-Al2O3 supports, the O 1s XPS spectra could also be deconvoluted into two peaks ascribed to Olatt and Oads, respectively. However, the O 1s XPS spectra of g-C3N4 and AC displayed only one peak centred at 531.2 and 532.7eV, respectively, which could be attributed to Oads. In addition, it can be found from Figure 5 that the binding energy of the crystal lattice oxygen (at around 529.1 eV) for 10% CoOx/g-C3N4 is lower than that for other samples, which may be resulted from the lower electronegativity of nitrogen compared to oxygen, that lead to an increase in the outer electron density of O and consequent decrease in binding energy.44 It is reported51, 52 that the nitrogen-enriched structure of g-C3N4 is a good 18


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electron donor, which can enhance the surface charge of CoOx through electron transfer, leading to the possessing the richness of oxygen species and cobalt species in the 10% CoOx /g-C3N4 catalyst. From Figure 5, it can be directly recognized that the peak area ratio of 529.1 and 530.8 eV in 10% CoOx/g-C3N4 is different with the other samples, indicates that the Oads/Olatt ratio are different in these samples. After eliminating the influence of the oxygen species derived from the supports by substraction method, the Oads/Olatt values have been calculated and listed in Table 2. Table 2 shows that the surface Oads/Olatt ratio of the samples followed the sequence of 10% CoOx/g-C3N4 > 10% CoOx/SBA-15 > 10% CoOx/γ-Al2O3 > 10% CoOx/AC. As can be seen, the surface Oads/Olatt ratio of 10% CoOx/g-C3N4 is much higher than in the other catalysts, indicating the partial removal of bonded O from the metal oxide as a consequence of N-doping in the Co3O4 lattice. This promotes the formation of oxygen vacancies,53 which may significantly alter the electronic properties, and thus the catalytic activity towards toluene oxidation. Table 2 XPS characterization results of different supported CoOx catalysts. Peak Samples

Co3+/Co2+

Oads/Olatt

Co2p

O1s

10% CoOx/g-C3N4

779.8/782.3

529.1/530.8

1.75

3.3

10% CoOx/SBA-15

779.7/782.4

532.5/533.9

1.57

2.6

10% CoOx/γ-Al2O3

779.8/782.4

530.5/532.2

1.55

1.8

10% CoOx/AC

779.3/782.1

529.6/531.3

1.42

0.8

* Oads/Olatt refers to the peak area ratio of surface adsorbed oxygen and lattice oxygen species.

3.6 Catalytic performance for toluene combustion The catalytic combustion of toluene was tested in the 100-400 °C temperature 19



Page 20 of 30

range with the different CoOx supported catalysts, and the results are shown in Figure 6. Regardless of the catalyst used, only CO2, H2O, and residual toluene can be detected in the outlet gas. The evaluation of the catalytic activity was conducted in a light-off experiment, the results of which are described by the curves shown in Figure 6. The values of T10, T50, and T90 are used as criteria for comparing the activity of the catalysts and are listed in Table 3. A blank test was carried on the quartz reactor loaded only with quartz wool, no toluene conversion was detected below 400 °C. Table 3 Catalytic activities in terms of T10, T50 and T90 over all catalysts for toluene oxidation Toluene conversion temperature/°C Samples

a

T10

T50

T90

g-C3N4

─

─

─

5% CoOx/g-C3N4

279.4

294.2

316.0

10% CoOx/g-C3N4

250.7

268.7

279.0

15% CoOx/g-C3N4

258.8

269.9

279.8

20% CoOx/g-C3N4

248.8

268.2

279.2

10% CoOx/SBA-15

268.5

292.7

315.0

10% CoOx/γ-Al2O3

284.9

313.4

335.8

10% CoOx/AC

313.2

347.9

384.0

T10, T50, T90 are ascribed to the temperature of 10%, 50%, and 90% toluene conversion,

respectively b

─ Out of studied range.

As shown in Figure 6(a), g-C3N4 can hardly catalyze the reaction as the toluene conversion obtained at 400 °C is less than 5%. After the loading of CoOx, toluene conversion increased with temperature and total oxidation of toluene was achieved below 320 °C. It should be noted that, no byproduct of incomplete combustion reactions was observed during the reaction process, the final products were always

20


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CO2 and H2O. Additionally, with the increase of CoOx loading from 5% to 10%, the light-off curve of toluene combustion shifted towards the low temperature, which indicates that the high loading of CoOx can significantly enhance the activity of the catalyst. But further increase in the CoOx loading did not bring any improvement in the catalytic efficiency, 15% CoOx/g-C3N4 exhibited similar catalytic activity for toluene combustion with that of 20% CoOx/g-C3N4. Figure 6(b) reports the light-off curves for toluene combustion carried out with the CoOx catalysts on different supports. Their catalytic activity, from highest to lowest, followed the sequence 10% CoOx/g-C3N4 > 10% CoOx/SBA-15> 10% CoOx/γ-Al2O3 > 10% CoOx/AC. More specifically, the complete combustion of toluene can be achieved at 279 °C over 10% CoOx/g-C3N4, whereas only 14%, 7%, and 3% toluene conversion was obtained over 10% CoOx/SBA-15, 10% CoOx/γ-Al2O3, and 10% CoOx/AC, respectively. The results fully demonstrated that 10% CoOx/g-C3N4 has excellent catalytic performance towards toluene combustion. 100 Toluene convsion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80

(a) 5% CoOx/g-C3N4 10% CoOx/g-C3N4

60

15% CoOx/g-C3N4 20% CoOx/g-C3N4

40

g-C3N4

20 0 100

150

200 250 300 o Temperature ( C )

21


350

400


100 Toluene convsion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

80 60

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(b) 10% CoOx/g-C3N4 10% CoOx/SBA-15 10% CoOx/γ-Al2O3 10% CoOx/AC

40 20 0 100

150

200 250 300 o Temperature ( C )

350

400

Figure 6. The catalytic activity of (a) the pristine g-C3N4 and CoOx/g-C3N4 catalyts; (b) different supported CoOx catalysts. Reaction conditions：catalyst weight = 50 mg, the concentration of toluene = 1000 ppm, total flow rate = 130 ml min-1, and GHSV = 10000 h-1. It is reported that the catalytic performance of supported cobalt catalysts towards VOC oxidation could be determined by different parameters, such as the CoOx particle size, the support property, and the reducibility of the cobalt species.42,

54

However, in the present work, the reaction results and TEM phots show that the catalytic activity of different CoOx catalysts is inconsistent with the particle size (Figure2). This indicates that the particle size is probably not a key factor for these supported CoOx catalyst in catalytic combustion of toluene. In order to understand what the 10% CoOx/g-C3N4 excellent catalytic activity is, we take an oxidation-reduction mechanism55 to express the steps of the VOCs combustion reaction: VOCs + oxidized catalyst → reduced catalyst + oxidized product

(1)

Reduced catalyst + O2 → oxidized catalyst

(2)

Thus, the ability of catalyst oxides to develop reduction/oxidation cycles and the adsorbed O2 density are two important factors in the VOCs combustion process. 22


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Combined with the results presented here, it is interestingly found that g-C3N4 could increase the adsorbed O2 density on the 10% CoOx/g-C3N4 catalysts (Figure5), which could explain the highest catalytic activity of 10% CoOx/g-C3N4 catalyst. Furthermore, the amount of spinel-structured Co3O4 with respect to Co3+ decreases in the order 10% CoOx/g-C3N4 > 10% CoOx/SBA-15> 10% CoOx/γ-Al2O3 > 10% CoOx/AC, which is well agreed with the activity order that was obtained from the catalytic combustion of toluene. According to the literature, the predominant formation of the Co3O4 oxide phase, along with the high reducibility of Co3+ at low temperature is advantageous for VOCs combustion,42,

56

and also contributed to

enhancing the catalytic activity of the 10% CoOx/g-C3N4 catalysts. These results therefore highlighted the outstanding promotional effect of g-C3N4 on the catalytic activity of CoOx in toluene combustion reaction, due to its unique physicochemical properties. Moreover, the stability of 10% CoOx/g-C3N4 was tested in catalytic combustion of toluene at different temperature stages (270 and 280 °C, two cycles) (Figure 7). The results show that the catalyst sustained the constant conversion of toluene under varying temperature conditions. The reusability of the catalyst was also tested, and the results obtained after carrying out the reaction for five cycles are shown in Figure 8, the conversion of toluene remained always at about 98%. These results indicate that 10% CoOx/g-C3N4 is an efficient and stable catalyst for catalytic combustion of toluene.

23



o

Toluene convsion(%)

100

o

280 C

280 C

80 60

o

270 C

o

270 C

40 20 0 0

6

12

18

24

30

36

Time on stream (h)

Figure 7. Time-on-stream stability of the catalytic combustion of toluene on 10% CoOx/g-C3N4 catalyst at different temperature stages. Reaction conditions：catalyst weight = 50 mg, the concentration of toluene = 1000 ppm, total flow rate = 130 ml min-1, and GHSV = 10000 h-1. 100

Toluene convsion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

80 60 40 20 0

1

2

3 4 Recycle Number

5

Figure 8. Results for recycling of 10% CoOx/g-C3N4 catalyst in the catalytic combustion of toluene. Reaction conditions ： catalyst weight = 50 mg, the concentration of toluene = 1000 ppm, total flow rate = 130 ml min-1, and GHSV = 10000 h-1. 4. Conclusions In summary, g-C3N4 was prepared and used as the support of CoOx for VOCs 24


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combustion, SBA-15, γ-Al2O3, and AC supported CoOx catalysts were prepared for comparison, and catalytic combustion of toluene was used as the probe reaction for the evaluation of catalytic performance. Reaction results shown that g-C3N4 supported CoOx with the CoOx loading of 10% exhibits the optimum catalytic activity, excellent stability, and good reusability compared with that of other CoOx/g-C3N4 samples. Based on a comparative analysis of the performance of SBA-15, γ-Al2O3, and AC supported CoOx catalysts, it was demonstrated that 10% CoOx/g-C3N4 performed better than the other formulations. This may be resulted from several factors, such as the presence of Co3O4 active phase, the high surface content of Co3+, the high density of surface oxygen adsorption species, and the facile reducibility of Co3+ at low temperature. The richness of N in the structure of g-C3N4 lead to a richness of electron on the surface of catalyst, which may be the reason of the stable exist of oxygen species and CoOx phases. Thus, g-C3N4 can be used as a good catalyst support for its excellent properties, and deserves further research and development. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (21776194 and 21606159) and Key Research and Development Program of Shanxi Province (201703D121022-1). Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI (1) N2 adsorption-desorption isotherms and pore size distributions. (2) H2-TPR 25



profiles of g-C3N4 and 10% CoOx/g-C3N4. (3) XPS spectra of 10% CoOx/g-C3N4: (a) Survey spectrum; (b) C1s; (c) N1s. (4) Peak positions in the H2-TPR profiles of different supported CoOx catalysts. References (1) Kampa, M.; Castanas, E. Human health effects of air pollution, Environ. Pollut. 2008, 151, 362. (2) Li, J. J.; Xu, X. Y.; Jiang, Z.; Hao, Z. P.; Hu, C. Nanoporous silica-supported nanometric palladium: synthesis, characterization, and catalytic deep oxidation of benzene, Environ. Sci. Technol. 2005, 39, 1319. (3) Peng, R.; Li, S.; Sun, X.; Ren, Q.; Chen, L.; Fu, M.; Wu, J.; Ye, D. Size effect of Pt nanoparticles on the catalytic oxidation of toluene over Pt/CeO2 catalysts, Appl. Catal. B-Environ. 2018, 220, 462. (4) Barakat, T.; Rooke, J. C.; Tidahy, H. L.; Hosseini, M.; Cousin, R.; Lamonier, J. F.; Giraudon, J. M.; De, P. G.; Weireld; Su, B. L.; Siffert, S. Noble-metal-based catalysts supported on zeolites and macro-mesoporous metal oxide supports for the total oxidation of volatile organic compounds, ChemSusChem 2011, 4, 1420. (5) Patterson, M. J.; Angove, D. E.; Cant, N. W. The effect of carbon monoxide on the oxidation of four C6 to C8 hydrocarbons over platinum, palladium and rhodium, Appl. Catal. B-Environ. 2000, 26, 47. (6) Scirè, S.; Liotta, L. F. Supported gold catalysts for the total oxidation of volatile organic compounds, Appl. Catal. B-Environ. 2012, 125, 222. (7) Yang, J. S.; Jung, W. Y.; Lee, G. D.; Park, S. S.; Jeong, E. D.; Kim, H. G.; Hong, S. S. Catalytic combustion of benzene over metal oxides supported on SBA-15, J. Ind. Eng. Chem. 2008, 14, 779. (8) Li, T. Y.; Chiang, S. J.; Liaw, B. J.; Chen, Y. Z. Catalytic oxidation of benzene over CuO/Ce1− xMnxO2 catalysts, Appl. Catal. B-Environ. 2011, 103, 143. (9) Li, W. B.; Wang, J. X.; Gong, H. Catalytic combustion of VOCs on non-noble metal catalysts, Catal. Today 2009, 148, 81. (10) Castaño, M. H.; Molina, R.; Moreno, S. Mn-Co-Al-Mg mixed oxides by auto-combustion method and their use as catalysts in the total oxidation of toluene, J. Mol. Catal. A-Chem. 2013, 370, 167. (11) Wyrwalski, F.; Lamonier, J. F.; Siffert, S.; Gengembre, L.; Aboukaïs, A. Modified Co3O4/ZrO2 catalysts for VOC emissions abatement, Catal. Today. 2006, 119, 332. (12) Liu, Q.; Wang, L. C.; Chen, M.; Cao, Y.; He, H. Y.; Fan, K. N. Dry citrate-precursor synthesized nanocrystalline cobalt oxide as highly active catalyst for total oxidation of propane, J. Catal. 2009, 263, 104. (13) Pozan, G. S. Effect of support on the catalytic activity of manganese oxide catalyts for toluene combustion, J. Hazard Mater. 2012, 221-222, 124. (14) Jiang, S.; Song, S. Enhancing the performance of Co3O4/CNTs for the catalytic combustion of toluene by tuning the surface structures of CNTs, Appl. Catal. B-Environ. 2013, 140-141, 1. (15) Huang, H.; Zhang, C.; Wang, L.; Li, G.; Song, L.; Li, G.; Tang, S.; Li, X. Promotional effect of HZSM-5 on the catalytic oxidation of toluene over MnO: X/HZSM-5 catalysts, Catal. Sci. 26


Page 26 of 30

Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Technol. 2016, 6, 4260. (16) Menon, U.; Poelman, H.; Bliznuk, V.; Galvita, V. V.; Poelman, D.; Marin, G. B. Nature of the active sites for the total oxidation of toluene by CuOCeO2/Al2O3, J. Catal. 2012, 295, 91. (17) Qu, Z.; Bu, Y.; Qin, Y.; Wang, Y.; Fu, Q. The effects of alkali metal on structure of manganese oxide supported on SBA-15 for application in the toluene catalytic oxidation, Chem. Eng. J. 2012, 209, 163. (18) Scirè, S.; Minicò, S.; Crisafulli, C.; Satriano, C.; Pistone, A. Catalytic combustion of volatile organic compounds on gold/cerium oxide catalysts, Appl. Catal. B-Environ. 2003, 40, 43. (19) Yu, D.; Liu, Y.; Wu, Z. Low-temperature catalytic oxidation of toluene over mesoporous MnO x-CeO2/TiO2 prepared by sol-gel method, Catal. Commun. 2010, 11, 788. (20) Gutiérrez-Ortiz, J. I.; López-Fonseca, R.; Aurrekoetxea, U.; González-Velasco, J. R. Low-temperature deep oxidation of dichloromethane and trichloroethylene by H-ZSM-5-supported manganese oxide catalysts, J. Catal. 2003, 218, 148. (21) Lin, L. Y.; Bai, H. Salt-induced formation of hollow and mesoporous CoOx/SiO2 spheres and their catalytic behavior in toluene oxidation, RSC Adv. 2016, 6, 24304. (22) Wu, G.; Thind, S. S.; Wen, J.; Kai, Y.; Chen, A. A novel nanoporous α-C3N4 photocatalyst with superior high visible light activity, Appl. Catal. B-Environ. 2013, 142-143, 590. (23) Chang, F.; Xie, Y.; Li, C.; Chen, J.; Luo, J.; Hu, X.; Shen, J. A facile modification of g-C3N4 with enhanced photocatalytic activity for degradation of methylene blue, Appl. Surf. Sci. 2013, 280, 967. (24) Miao, X.; Lei, H.; Dong, S. Facile fabrication of highly efficient g-C3N4/Ag2O heterostructured photocatalysts with enhanced visible-light photocatalytic activity, ACS. Appl. Mater. Inter. 2013, 5, 12533. (25) Lin, X.; Zhao, S.; Chen, Y.; Fu, L.; Zhu, R.; Liu, Z. Nitrogen-doped carbon cobalt grafted on graphitic carbon nitride catalysts with enhanced catalytic performance for ethylbenzene oxidation, J. Mol. Catal. A-Chem. 2016, 420, 11. (26) Wang, J.; Li, C.; Cong, J.; Liu, Z.; Zhang, H.; Liang, M.; Gao, J.; Wang, S.; Yao, J. Facile synthesis of nanorod-type graphitic carbon nitride/Fe2O3 composite with enhanced photocatalytic performance, J. Solid State Chem. 2016, 238, 246. (27) Muniandy, L.; Adam, F.; Mohamed, A. R.; Iqbal, A.; Rahman, N. R. A. Cu2+ coordinated graphitic carbon nitride (Cu-g-C3N4 ) nanosheets from melamine for the liquid phase hydroxylation of benzene and VOCs, Appl. Surf. Sci. 2017, 398, 43. (28) Shi, Y.; Hu, X.; Zhao, J.; Zhou, X.; Zhu, B.; Zhang, S.; Huang, W. CO oxidation over CuO deposited on 2D continuous lamellar g-C3N4, New. J. Chem. 2015, 39, 6642. (29) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light, Nat. Mater. 2009, 8, 76. (30) Jiang, J.; Lei, O. Y.; Zhu, L.; Zheng, A.; Zou, J.; Yi, X.; Tang, H. Dependence of electronic structure of g-C3N4 on the layer number of its nanosheets: A study by Raman spectroscopy coupled with first-principles calculations, Carbon 2014, 80, 213. (31) Chang, X.; Wang, T.; Zhang, P.; Zhang, J.; Li, A.; Gong, J. Enhanced surface reaction kinetics and charge separation of p-n heterojunction Co3O4/BiVO4 photoanodes, J. Am. Chem. Soc. 2015, 137, 8356. (32) Shinde, S. S.; Sami, A.; Lee, J. H. Sulfur mediated graphitic carbon nitride/S-Se-graphene as 27



a metal- free hybrid photocatalyst for pollutant degradation and water splitting, Carbon 2016, 96, 929. (33) Q Xiang, Q.; Yu, J.; Jaroniec, M. Preparation and enhanced visible-light photocatalytic H2-production activity of graphene/C3N4 composites, J. Phys. Chem. C 2011, 115, 7355. (34) Xing†, Y. Synthesis and electrochemical characterization of uniformly-dispersed high loading Pt nanoparticles on sonochemically-treated carbon nanotubes, J. Phys. Chem. B 2007, 108, 19255. (35) Zhang, P.; Jiang, F.; Chen, H. Enhanced catalytic hydrogenation of aqueous bromate over Pd/mesoporous carbon nitride, Chem. Eng. J. 2013, 234, 195. (36) Xiong, H.; Zhang, Y.; Liew, K.; Li, J. Fischer-Tropsch synthesis: The role of pore size for Co/SBA-15 catalysts, J. Mol. Catal. A-Chem. 2008, 295, 68. (37) Borg, Ø.; Eri, S.; Blekkan, E. A.; Storsæter, S.; Wigum, H.; Rytter, E.; Holmen, A. Fischer-Tropsch synthesis over γ-alumina-supported cobalt catalysts: effect of support variables, J. Catal. 2007, 248, 89. (38) Wang, Y.; Wang, X.; Antonietti, M. Polymeric graphitic carbon nitride as a heterogeneous organocatalyst: from photochemistry to multipurpose catalysis to sustainable chemistry, Angew. Chem. Int. Edit. 2012, 51, 68. (39) Tang, Q.; Zhang, Q.; Wang, P.; Wang, Y.; Wan, H. Characterizations of cobalt oxide nanoparticles within faujasite zeolites and the formation of metallic cobalt, Chem. Mater. 2004, 16, 1967. (40) Wang, C.; Lim, S.; Du, G.; Loebicki, C. Z.; Li, N.; Derrouiche, S.; Haller, G. L. Synthesis, characterization, and catalytic performance of highly dispersed Co-SBA-15, J. Phys. Chem. C 2009, 113, 14863. (41) Khassin, A. A.; Yurieva, T. M.; Kustova, G. N.; Itenberg, I. S.; Demeshkina, M. P.; Krieger, T. A.; Plyasova, L. M.; Chermashentseva, G. K.; Parmon, V. N. Cobalt-aluminum co-precipitated catalysts and their performance in the Fischer-Tropsch synthesis, J. Mol. Catal. A-Chem. 2001, 168, 193. (42) Wu, H.; Pantaleo, G.; Carlo, G. D.; Guo, S.; Marcì, G.; Concepcion, P.; Venezia, A. M.; Liotta, L. F. Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agent and calcination temperature on catalytic activity for methane oxidation, Catal. Sci. Technol. 2015, 5, 1888. (43) Zhu, Z.; Lu, G.; Zhang, Z.; Guo, Y.; Guo, Y.; Wang, Y. Highly active and stable Co3O4/ZSM-5 catalyst for propane oxidation: effect of the preparation method, ACS. Catal. 2013, 3, 1154. (44) Yu, Y.; Zhong, Q.; Cai, W.; Ding, J. Promotional effect of N-doped CeO2 supported CoOx catalysts with enhanced catalytic activity on NO oxidation, J. Mol. Catal. A-Chem. 2015, 398, 344. (45) Zhang, X.; Xie, X.; Wang, H.; Zhang, J.; Pan, B.; Xie, Y. Enhanced photoresponsive ultrathin graphitic-phase C3N4 nanosheets for bioimaging, J. Am. Chem. Soc. 2013, 135, 18. (46) Thomas, A.; Fischer, A.; Goettmann, F.; Antonietti, M.; Mueller, J. O.; Schloegl, R.; Carlsson, J. M. Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts, J. Mater. Chem. 2008, 18, 4893. (47) Wang, B.; Zhang, J.; Huang, F. Enhanced visible light photocatalytic H2 evolution of metal-free g-C3N4/SiC heterostructured photocatalysts, Appl. Surf. Sci. 2017, 391, 449. (48) Bai, B.; Arandiyan, H.; Li, J. Comparison of the performance for oxidation of formaldehyde 28


Page 28 of 30

Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


on nano-Co3O4, 2D-Co3O4, and 3D-Co3O4 catalysts, Appl. Catal. B-Environ. 2013, 142-143, 677. (49) Xia, Y.; Dai, H.; Jiang, H.; Zhang, L. Three-dimensional ordered mesoporous cobalt oxides: Highly active catalysts for the oxidation of toluene and methanol, Catal. Commun. 2010, 11, 1171. (50) Bai, B.; Li, J. Positive effects of K+ ions on three-dimensional mesoporous Ag/Co3O4 catalyst for HCHO oxidation. ACS. Catal. 2014, 4, 2753. (51) Tonda, S.; Kumar, S.; Shanker, V. Surface plasmon resonance-induced photocatalysis by Au nanoparticles decorated mesoporous g-C3N4 nanosheets under direct sunlight irradiation, Mater. Res. Bull. 2016, 75, 51. (52) Deng, D.; Yang, Y.; Gong, Y.; Li, Y.; Xu, X.; Wang, Y. Palladium nanoparticles supported on mpg-C3N4 as active catalyst for semihydrogenation of phenylacetylene under mild conditions, Green Chem. 2013, 15, 2525. (53) Xu, L.; Wang, Z.; Wang, J.; Xiao, Z.; Huang, X.; Liu, Z.; Wang, S. N-doped nanoporous Co3O4 nanosheets with oxygen vacancies as oxygen evolving electrocatalysts, Nanotechnology 2017, 28, 165402. (54) Kim, S. C.; Jung, H. Y.; Nah, J. W.; Park, Y. K. Complete oxidation of toluene over supported palladium catalysts: effect of support, J. Nanosci. Nanotechno. 2016, 16, 4638. (55) Alvarez-Merino, M. A.; Ribeiro, M. F.; Silva, J. M.; Carrasco-Marín, F.; Maldonado-Hódar, F. J. Activated carbon and tungsten oxide supported on activated carbon catalysts for toluene catalytic combustion, Environ. Sci. Technol. 2004, 38, 4664. (56) Mu, Z.; Li, J. J.; Duan, M. H.; Hao, Z. P.; Qiao, S. Z. Catalytic combustion of benzene on Co/CeO2/SBA-15 and Co/SBA-15 catalysts, Catal. Commun. 2008, 9, 1874.

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Catalytic combustion of toluene over cobalt oxides supported on

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