Bimetallic Pt-Co Nanoparticle Deposited on Alumina for Simultaneous CO and Toluene Oxidation in the Presence of Moisture

: Carbon monoxide (CO) and hydrocarbons (HCs) generally have competitive adsorption on the active site of noble-metal nano-catalysts, thus developing an effective way to reduce the passivation of competitive reaction with each other is an urgent problem. In this study, we successfully synthesized transition metal-noble metal (Pt-M) alloys via introducing inexpensive metal elements (M = Ni, Co and Cu) into Pt particles and then deposited on alumina support to form Pt-based catalysts. Subsequently, we choose CO and toluene as polluting gases to evaluate the catalytic activities of Pt-M/Al 2 O 3 catalysts. Introducing inexpensive metal elements (M = Ni, Co, and Cu) signiﬁcantly changed the physicochemical properties and catalytic activities of these Pt-based catalysts. It can be found that the Pt-Co/Al 2 O 3 catalyst exhibited outstanding catalytic activity for CO and toluene oxidation under mixed gas atmosphere, compared with other Pt-based catalysts, which is due to the higher dispersity, more surface adsorption oxygen, and well redox ability. Surprisingly, H 2 O could promote the catalytic activities for CO/toluene co-oxidation over the Pt-Co/Al 2 O 3 catalyst. Thus, the present synthetic strategy not only opens an avenue towards the synthesis of noble metal-based catalysts, but also provides an excellent tolerance to H 2 O in the catalytic process.


Introduction
In recent years, with the progress of industrial development and the increased number of vehicles, the concentration of carbon monoxide (CO) and hydrocarbons (HCs) in ambient air is on the rise, causing the frequent occurrence of photochemical smog pollution in some areas and seriously threatening people's health [1][2][3][4][5][6][7][8][9]. However, controlling CO and HCs exhaust emissions can be an important direction to reducing air pollution. At present, there are many technical methods for controlling volatile organic compounds (VOCs), such as adsorption, catalytic oxidation, combustion, plasma, and so on. Among them, catalytic oxidation is known as the most efficient and economical method to remove VOCs [10][11][12][13][14]. Besides, catalytic oxidation has also been recognized as a promising technology for reducing exhaust gases because it directly converts pollutions into CO 2 and H 2 O at relatively lower temperatures and reduces the production of other atmospheric pollutants. Precious metal catalysts and non-precious metal oxide catalysts are the most studied catalytic materials for CO and VOCs oxidation, but Pt-based catalysts are the preferred candidates due to their excellent catalytic properties [15,16]. To date, the commercial 3-way (Pt-Pd-Rh) catalysts have been widely used in the after-treatment system, but the catalytic converters realize the complete removal of CO and HCs exhaust emission at a high-temperature range (300-400 • C) [17]. Significantly, CO and HCs have competitive adsorption on the active sites of catalysts, and the catalytic performance of noble metal catalysts for CO oxidation The XRD patterns of as-synthesized Pt/Al 2 O 3 and Pt-M/Al 2 O 3 samples are shown in Figure S1. From the XRD spectra of four samples, it can be seen that each sample contains four distinct diffraction peaks at 37.   Figure 1a were consistent with type IV isotherms with an H3-type hysteresis loop, indicating a mesoporous structure. The pores of these samples can be seen from the distribution of pore size in Figure 1b. It suggests that each sample is a mesoporous material. The mesoporous structure data of all the samples are summarized in Table 1. The samples have larger surface areas in the range of 205.99~303.34 m 2 g −1 . Compared to the Al 2 O 3 support, it can be found that the surface areas of Pt/Al 2 O 3 and Pt-M/Al 2 O 3 catalysts decreased slightly, and the pore volumes also decreased slightly between 0.91 cm 3 g −1 and 0.73 cm 3 g −1 . It is worth noting that pure Al 2 O 3 possessed the largest surface area and pore volume among all the samples. The reason for this result may be that metal particles on the surface of Pt/Al 2 O 3 and Pt-M/Al 2 O 3 catalysts may hinder the pore channel of Al 2 O 3 support. It is well known that the surface area has an effect on the catalytic activity of most reactions, and the catalysts with larger surface areas have better catalytic activity. In addition, abundant pore structure will be more favorable for the exposure of active sites, thereby facilitating the adsorption and reaction of reactants. However, for these Pt-M/Al 2 O 3 catalysts, the surface area and pore structure may not be the crucial factors in the CO/toluene oxidation.

Microstructure
It is believed that the particle sizes and dispersions of Pt nanoparticles are also pivotal factors to influence the catalytic properties of these catalysts. Transmission electron microscopy (TEM) measurement was carried out to further reveal microstructures of Pt/Al 2 O 3 and Pt-M/Al 2 O 3 samples, as shown in Figure 2. Insets show the size distributions of Ptbased nanoparticles in Figure 2a-d, with the nanoparticles uniformly distributed on the surface of catalysts. These particles calculated from the histograms in Figure 2 (Figure 2e) clearly reveals that the surface lattice spacing is measured to be 0.215 nm, which is matched well with the (111) crystal face of Pt phase. For the Pt-Ni/Al 2 O 3 catalyst, the surface lattice spacing of 0.200 nm is measured in Figure 2f, which is consistent with the (111) lattice plane of Pt. The HRTEM image of Pt-Co/Al 2 O 3 shows the surface lattice spacing in Figure 2g, and the measured d-spacing is 0.260 nm, consistent with the (200) lattice plane of Pt. For the Pt-Cu/Al 2 O 3 catalyst (Figure 2d,h), there is the surface lattice spacing with a d-spacing of 0.230 nm, which is matched well with the (200) crystal plane of the Pt phase. From the TEM/HRTEM images of all the catalysts, introducing inexpensive metal elements (M = Ni, Co, Cu) could be used to control the average size of metal Pt nanoparticles. In addition, MO x phases are not observed, which is due to the lower loading or the formation of intermetallic compounds between Pt and MO x .

Microstructure
It is believed that the particle sizes and dispersions of Pt nanoparticles are also pivo factors to influence the catalytic properties of these catalysts. Transmission electron m croscopy (TEM) measurement was carried out to further reveal microstructures Pt/Al2O3 and Pt-M/Al2O3 samples, as shown in Figure 2. Insets show the size distributio of Pt-based nanoparticles in Figure 2a

Temperature Programmed Reduction (TPR)
In Figure 3, the H 2 -TPR results describe different forms and reduction behaviors of these Pt-based samples. Guo et al. reported that Pd/Al 2 O 3 possessed negative peaks that were corresponded to the decomposition of the β-PdH phase, confirmed the existence of metallic Pd nanoparticles [29,30]. In addition, the H 2 desorption peak at higher temperatures indicates that some Pd species are easily reduced at normal temperature. In this work, H 2 -TPR results show that one negative peak was observed at about 70-100 • C, and one positive peak was detected at about 450-500 • C for these catalysts. Fu et al. [31] revealed that many Co oxide species loaded onto Pt NPs to form a nanoalloy can be reduced at 100 • C. Regalbuto et al. [32] reported that alloying Pt-M (Co, Ni, Cu) was enabled to observe hydrogen spillover. Thus, the negative peak could be the characteristic peak of hydrogen desorption due to the effect of metal Pt particles. The positive peak at high temperatures could be attributed to the reduction of lattice oxygen species on the surface of Al 2 O 3 . Of course, these positive characteristic peaks at about 450-500 • C can be considered as the reduction peaks of surface lattice oxygen on these catalysts. The above temperature regions of H 2 desorption peak over Pt-M/Al 2 O 3 catalysts are similar to those of Pd/Al 2 O 3 catalysts reported by Guo et al. [30]. Among these catalysts, the negative peak over the Pt-Co/Al 2 O 3 catalyst slightly shifted to a higher temperature (93 • C), manifesting that the Pt species in Pt-Co/Al 2 O 3 catalyst could still be easily reduced at lower temperatures. In addition, the addition of transition metal can cause the reduction peak to move slightly, and the intensity of hydrogen consumption at about 450-500 • C on the Pt-M/Al 2 O 3 catalysts is obviously decreased, which is mainly caused by the electronic interaction between transition metal oxides (MO x ) and Pt nanoparticles.

Temperature Programmed Reduction (TPR)
In Figure 3, the H2-TPR results describe different forms and reduction behaviors of these Pt-based samples. Guo et al. reported that Pd/Al2O3 possessed negative peaks that were corresponded to the decomposition of the β-PdH phase, confirmed the existence of metallic Pd nanoparticles [29,30]. In addition, the H2 desorption peak at higher temperatures indicates that some Pd species are easily reduced at normal temperature. In this work, H2-TPR results show that one negative peak was observed at about 70-100 °C, and one positive peak was detected at about 450-500 °C for these catalysts. Fu et al. [31] revealed that many Co oxide species loaded onto Pt NPs to form a nanoalloy can be reduced at 100 °C. Regalbuto et al. [32] reported that alloying Pt-M (Co, Ni, Cu) was enabled to observe hydrogen spillover. Thus, the negative peak could be the characteristic peak of hydrogen desorption due to the effect of metal Pt particles. The positive peak at high temperatures could be attributed to the reduction of lattice oxygen species on the surface of Al2O3. Of course, these positive characteristic peaks at about 450-500 °C can be considered as the reduction peaks of surface lattice oxygen on these catalysts. The above temperature regions of H2 desorption peak over Pt-M/Al2O3 catalysts are similar to those of Pd/Al2O3 catalysts reported by Guo et al. [30]. Among these catalysts, the negative peak over the Pt-Co/Al2O3 catalyst slightly shifted to a higher temperature (93 °C), manifesting that the Pt species in Pt-Co/Al2O3 catalyst could still be easily reduced at lower temperatures. In addition, the addition of transition metal can cause the reduction peak to move slightly, and the intensity of hydrogen consumption at about 450-500 °C on the Pt-M/Al2O3 catalysts is obviously decreased, which is mainly caused by the electronic interaction between transition metal oxides (MOx) and Pt nanoparticles.

Surface Element Composition
To further investigate the surface composition of these Pt-based catalysts, X-ray photoelectron spectra (XPS) measurement was tested on the four samples. Figure 4 illustrates Al 2p/Pt 4f and O1s XPS spectra of all the samples. Since the characteristic peaks of Al 2p and Pt 4f were close and overlapped in the range of 73~75 eV, thus the valency of platinum was not determined from Figure 4a. XPS spectra of O 1s were also further analyzed, and

Surface Element Composition
To further investigate the surface composition of these Pt-based catalysts, X-ray photoelectron spectra (XPS) measurement was tested on the four samples. Figure 4 illustrates Al 2p/Pt 4f and O1s XPS spectra of all the samples. Since the characteristic peaks of Al 2p and Pt 4f were close and overlapped in the range of 73~75 eV, thus the valency of platinum was not determined from Figure 4a. XPS spectra of O 1s were also further analyzed, and three oxygen chemical states were observed on the surface of Pt-based catalysts, as shown in Figure 4b. Wherein, the main peak with an O 1s spectrum appears in the position of binding energy (BE) of around 531.1 eV, which was related to lattice oxygen species (O latt ) [33,34]. While the peak at 532.2 eV was considered to be surface absorbed oxygen species (O ads ), and the weak peak at 533 eV was ascribed to adsorbed hydroxyl and water molecules (O -OH ). Besides, the proportion of three oxygen chemical states over these samples was calculated, the results are shown in Table 2

Oxygen Temperature-Programmed Desorption (O2-TPD)
O2-TPD experiments were performed to understand their O2 desorption behavior, as shown in Figure 5. Three distinct desorption peaks could be seen on four catalysts, corresponding to different desorption oxygen species. The conversion process of oxygen adsorption on a catalyst was followed [35][36][37] Thus, it can be seen that these different states of oxygen on the surface of catalysts. Three distinct peaks were observed at about 170 ~ 210 °C, 400 ~ 420 °C, and 500 ~ 550 °C. A α strong peak in the range of 100 ~ 300 °C was regarded as the physically surface-adsorbed oxygen species and adsorbed O2 − species (ads-O2 and ads-O2 − , respectively) [36,38,39]. A β peak in between 300 and 450 °C was assigned to surface lattice species (latt-O 2− ), while the third peak (γ peak in between 450 and 600 °C) belongs to the pyrolysis of lattice oxygen at high temperature [40]. If the catalyst with α peak at a lower temperature level indicated that there could be more likely to produce surface oxygen species, which will provide higher catalytic activity. Generally speaking, a material with abundant reactive oxygen species can perform a redox reaction at lower temperatures, and the high-temperature oxygen fluidity can improve the efficiency of transporting oxygen species. As everyone knows that the oxidation process of VOCs mainly follows a Mars-van Krevelen mechanism and the reaction occurs due to a nucleophilic attack of surface absorbed oxygen species [41,42]. Meanwhile, the higher levels of surface active-oxygen species were conducive to VOCs oxidation [40,[43][44][45]. Abundant surface oxygen vacancies could facilitate the formation of surface adsorbed oxygen species, which was verified by measuring the higher oxygen vacancy molar ratios of catalysts via XPS results in this study. Therefore, the strong desorption peak (α peak) of Pt-Co/Al2O3 suggests that more surface adsorption

Oxygen Temperature-Programmed Desorption (O 2 -TPD)
O 2 -TPD experiments were performed to understand their O 2 desorption behavior, as shown in Figure 5. Three distinct desorption peaks could be seen on four catalysts, corresponding to different desorption oxygen species. The conversion process of oxygen adsorption on a catalyst was followed [35][36][37]: O 2 (ads) → O 2 − (ads) → O 2− (ads) → O 2− (latt). Thus, it can be seen that these different states of oxygen on the surface of catalysts. Three distinct peaks were observed at about 170~210 • C, 400~420 • C, and 500~550 • C. A α strong peak in the range of 100~300 • C was regarded as the physically surface-adsorbed oxygen species and adsorbed O 2 − species (ads-O 2 and ads-O 2 − , respectively) [36,38,39]. A β peak in between 300 and 450 • C was assigned to surface lattice species (latt-O 2− ), while the third peak (γ peak in between 450 and 600 • C) belongs to the pyrolysis of lattice oxygen at high temperature [40]. If the catalyst with α peak at a lower temperature level indicated that there could be more likely to produce surface oxygen species, which will provide higher catalytic activity. Generally speaking, a material with abundant reactive oxygen species can perform a redox reaction at lower temperatures, and the high-temperature oxygen fluidity can improve the efficiency of transporting oxygen species. As everyone knows that the oxidation process of VOCs mainly follows a Mars-van Krevelen mechanism and the reaction occurs due to a nucleophilic attack of surface absorbed oxygen species [41,42]. Meanwhile, the higher levels of surface active-oxygen species were conducive to VOCs oxidation [40,[43][44][45]. Abundant surface oxygen vacancies could facilitate the formation of surface adsorbed oxygen species, which was verified by measuring the higher oxygen vacancy molar ratios of catalysts via XPS results in this study. Therefore, the strong desorption peak (α peak) of Pt-Co/Al 2 O 3 suggests that more surface adsorption oxygen can be provided by the Pt-Co/Al 2 O 3 catalyst, resulting in the catalytic performance of CO/toluene oxidation being improved significantly.  Figure 6 shows the catalytic activities for CO/toluene of Pt-based samples un ferent reaction conditions as a function of temperature, while the CO/toluene con plots were recorded at the heat preservation stage for 1.0 h. CO2 and H2O were th products, while other by-products (below 1.0 ppm) were not detected. The catalyt ities of these samples were compared by using T10, T50, and T99 (the catalytic tempe of 10%, 50%, and 99% CO/toluene conversion, respectively) as a reference, as desc Table 3. It can be found that all the catalysts have more outstanding catalytic a than Pt/Al2O3 (T99 = 180 °C) for individual CO oxidation in Figure 6a, their T99 va CO oxidation were achieved at 160 °C with a WHSV of 60,000 mL g −1 h −1 . For ind toluene oxidation, Pt-Co/Al2O3 catalyst exhibited an optimal catalytic activity amon Pt-based catalysts in Figure 6b, its T10, T50, T99 are 160, 180, and 195 °C, respectively ever, the catalytic performance of bimetallic Pt-Ni/Al2O3 and Pt-Cu/Al2O3 catalysts uene oxidation was reduced, compared with the Pt/Al2O3 catalyst. However, w and toluene gases simultaneously exist in the reaction gases stream, the catalytic a for CO and toluene oxidation over all the catalysts were inhibited due to the com  Figure 6 shows the catalytic activities for CO/toluene of Pt-based samples under different reaction conditions as a function of temperature, while the CO/toluene conversion plots were recorded at the heat preservation stage for 1.0 h. CO 2 and H 2 O were the main products, while other by-products (below 1.0 ppm) were not detected. The catalytic activities of these samples were compared by using T 10 , T 50 , and T 99 (the catalytic temperatures of 10%, 50%, and 99% CO/toluene conversion, respectively) as a reference, as described in Table 3. It can be found that all the catalysts have more outstanding catalytic activities than Pt/Al 2 O 3 (T 99 = 180 • C) for individual CO oxidation in Figure 6a, their T 99 values for CO oxidation were achieved at 160 • C with a WHSV of 60,000 mL g −1 h −1 . For individual toluene oxidation, Pt-Co/Al 2 O 3 catalyst exhibited an optimal catalytic activity among these Pt-based catalysts in Figure 6b, its T 10 , T 50 , T 99 are 160, 180, and 195 • C, respectively. However, the catalytic performance of bimetallic Pt-Ni/Al 2 O 3 and Pt-Cu/Al 2 O 3 catalysts for toluene oxidation was reduced, compared with the Pt/Al 2 O 3 catalyst. However, when CO and toluene gases simultaneously exist in the reaction gases stream, the catalytic activities for CO and toluene oxidation over all the catalysts were inhibited due to the competitive adsorption of CO and toluene on the same active sites, as shown in Figure 6c and d. In addition, it can be found that there was an inverse hysteresis in CO or toluene conversion during catalytic oxidation over Pt-Co/Al 2 O 3 catalyst in Figure S2, which was due to exothermic combustion. The Pt/Al 2 O 3 catalyst exhibited complete oxidation for CO and toluene co-existence at 200 • C. Among bimetallic Pt-M/Al 2 O 3 catalysts, Pt-Co/Al 2 O 3 catalyst exhibited a more excellent catalytic activity for CO and toluene oxidation in mixture conditions, while Pt-Ni/Al 2 O 3 and Pt-Cu/Al 2 O 3 catalysts displayed a poorer CO and toluene oxidation activity than the Pt/Al 2 O 3 catalyst. The presence of toluene caused an obvious decrease in CO conversion due to competitive adsorption of both CO and toluene on the surface of catalysts. Moreover, Platinum atoms exposed on the surface of catalytic materials were often considered as the active site for controlling the catalytic oxidation of CO/toluene. The TOF values for CO/toluene co-oxidation at 190 • C have also been calculated in Figure 7. With the increased dispersity of Pt in bimetallic catalysts, the Pt-based catalysts would effectively increase the catalytic activity and TOF of each active site. Therefore, the Pt-Co/Al 2 O 3 catalyst with the highest dispersity and TOF value exhibited the best catalytic performances for CO/toluene oxidation at a lower temperature.

The Effects of WHSV and Moisture
The effect of WHSV on the catalytic activities of Pt-Co/Al 2 O 3 catalyst for CO/toluene oxidation was further investigated, as shown in Figure 8. With the increase in WHSV values, the catalytic activities of CO/toluene oxidation decreased. Under the condition of WHSV = 30,000 mL g −1 h −1 , the temperature of complete oxidation for individual CO and toluene oxidation could be obtained at a temperature of 160 and 190 • C, respectively, whereas the T 99 values for CO and toluene oxidation in mixture conditions were about 170 and 190 • C, respectively. When the WHSV value was further increased to 120,000 mL g −1 h −1 , the Pt-Co/Al 2 O 3 catalyst can completely degrade the CO and toluene at below 220 • C.
To simulate more realistic conditions, certain moisture was introduced into the simulated off-gas stream, which could obviously affect the catalytic performance of catalyst. The influence of moisture on the catalytic activities of the Pt-Co/Al 2 O 3 catalyst for CO/toluene oxidation are showed in Figure 9. Surprisingly, it can be found that H 2 O promotes the catalytic activities for CO/toluene oxidation over the Pt-Co/Al 2 O 3 catalyst. In addition, the promoting effect of H 2 O in individual CO/toluene oxidation is more remarkable than that in CO and toluene co-oxidation. For individual CO/toluene oxidation with moisture, Pt-Co/Al 2 O 3 catalyst maintains full CO and toluene conversions at a temperature of 150 • C and 190 • C, respectively. Under the mixture conditions with moisture, the CO and toluene conversions would be mildly facilitated by moisture. Therefore, it can be seen from the experimental data that the Pt-Co/Al 2 O 3 catalyst owns an excellent tolerance to H 2 O in the oxidation process, and H 2 O also have a similar promoting effect on other catalysts [44,[46][47][48].
oxidation was further investigated, as shown in Figure 8. With the increase in WHSV values, the catalytic activities of CO/toluene oxidation decreased. Under the condition of WHSV = 30,000 mL g −1 h −1 , the temperature of complete oxidation for individual CO and toluene oxidation could be obtained at a temperature of 160 and 190 °C, respectively, whereas the T99 values for CO and toluene oxidation in mixture conditions were about 170 and 190 °C, respectively. When the WHSV value was further increased to 120,000 mL g −1 h −1 , the Pt-Co/Al2O3 catalyst can completely degrade the CO and toluene at below 220 °C.  To simulate more realistic conditions, certain moisture was introduced into the simulated off-gas stream, which could obviously affect the catalytic performance of catalyst. The influence of moisture on the catalytic activities of the Pt-Co/Al2O3 catalyst for CO/toluene oxidation are showed in Figure 9. Surprisingly, it can be found that H2O promotes the catalytic activities for CO/toluene oxidation over the Pt-Co/Al2O3 catalyst. In addition, the promoting effect of H2O in individual CO/toluene oxidation is more remarkable than that in CO and toluene co-oxidation. For individual CO/toluene oxidation with moisture, Pt-Co/Al2O3 catalyst maintains full CO and toluene conversions at a temperature of 150 °C and 190 °C, respectively. Under the mixture conditions with moisture, the CO and toluene conversions would be mildly facilitated by moisture. Therefore, it can be seen from the experimental data that the Pt-Co/Al2O3 catalyst owns an excellent tolerance to H2O in the oxidation process, and H2O also have a similar promoting effect on other catalysts [44,[46][47][48].  Figure S3 shows an on-stream stability experiment for CO/toluene oxidation over the Pt-Co/Al2O3 catalyst at different conditions under a WHSV of 60,000 mL g −1 h −1 . During the long-term stability test for 48 h, the conversions of CO and toluene over the Pt-Co/Al2O3 catalyst under dry conditions at a temperature 200 °C were found to be 100% and 98% in Figure S3a, respectively, which were not significantly decreased. Besides, their CO and toluene conversions with or without H2O under mixture conditions at a temperature of 180 °C did not fluctuate significantly in Figure S3b. The above results manifest  Figure S3 shows an on-stream stability experiment for CO/toluene oxidation over the Pt-Co/Al 2 O 3 catalyst at different conditions under a WHSV of 60,000 mL g −1 h −1 . During the long-term stability test for 48 h, the conversions of CO and toluene over the Pt-Co/Al 2 O 3 catalyst under dry conditions at a temperature 200 • C were found to be 100% and 98% in Figure S3a, respectively, which were not significantly decreased. Besides, their CO and toluene conversions with or without H 2 O under mixture conditions at a temperature of 180 • C did not fluctuate significantly in Figure S3b. The above results manifest that the Pt-Co/Al 2 O 3 catalyst exhibits a relatively high catalytic activity for CO/toluene oxidation, good stability as well as high resistance to CO and hydrocarbon inhibition in the simulated exhaust stream, indicating that the Pt-Co/Al 2 O 3 catalyst can be well applied to CO and toluene co-oxidation.

Conclusions
In summary, we have successfully synthesized bimetallic Pt-M (M = Ni, Co, Cu) on alumina substrates via introducing inexpensive metal elements for the catalytic removal of CO and toluene co-existence. It can be found that introducing inexpensive metal elements into Pt/Al 2 O 3 catalyst clearly changes the physico-chemical properties, anti-toxic abilities, and catalytic performances for CO and toluene co-oxidation. The catalytic evaluations of CO/toluene oxidation indicate that the Pt-Co/Al 2 O 3 catalyst exhibits the best catalytic activity for complete CO and toluene oxidation (T 99/CO = 160 • C, T 99/toluene = 200 • C) under individual atmosphere among these Pt-based catalysts. Moreover, the bimetallic Pt-M/Al 2 O 3 catalysts display identical catalytic performance (T 99/CO = 160 • C) for individual CO oxidation, which is higher than the Pt/Al 2 O 3 catalyst. For CO and toluene co-oxidation, the Pt-Co/Al 2 O 3 catalyst also had the lowest temperature, and CO and toluene have competitive adsorption at the active sites of catalysts. Importantly, H 2 O promotes the catalytic activities for CO/toluene oxidation over the Pt-Co/Al 2 O 3 catalyst due to excellent tolerance to H 2 O. According to the catalytic and characterization analysis, it can be seen that Pt-Co/Al 2 O 3 catalyst with superior activity has the highest turnover frequency (TOF) for CO/toluene conversion and the well dispersity of Pt particles. In addition, the catalytic performance is related to the Pt particle size, metal species, more surface adsorption oxygen, and well redox ability. However, the pathway introducing Ni and Cu elements into Pt/Al 2 O 3 to prepare Pt-Ni/Al 2 O 3 and Pt-Cu/Al 2 O 3 do not achieve the desired goal of increasing catalytic activity for simultaneous CO and toluene oxidation and the synthesis of Pt-based catalysts decorating a low content of Co metal element is a useful method to improve Pt-metal utilization in the CO and toluene oxidation.
Funding: This research described above was financially supported by the research funds of "China Postdoctoral Science Foundation, grant number 2020M683629XB" and "National Natural Science Foundation of China, grant number 51978189".

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.