1 Introduction

Catalytic oxidation of carbon monoxide (CO) not only plays a critical role in heterogeneous catalysis as a classic model reaction but also shows major practical potential in automotive catalysts, air cleaners, and gas mask applications, as it is an effective method for toxic CO gas removal [1,2,3]. Research on catalytic CO oxidation has gained increasing attention in recent years, with a particular focus on noble metal platinum group catalysts [4,5,6,7,8,9]. Noble metal platinum (Pt) species serve as active sites in the adsorption of CO during CO oxidation reaction. CO molecules are strongly adsorbed on the Pt atoms through the Langmuir–Hinshelwood mechanism and subsequently combined with the surface oxygen atom to form carbon dioxide (CO2), which has been clarified as the crucial rate-determining step of the CO oxidation reaction [10, 11]. Nevertheless, the excessive adsorbed CO can hinder the O2 adsorption and activation to some extent, resulting in an effect known as CO poisoning, which leads to reduced catalytic efficiency [12,13,14].

To solve the CO poisoning on Pt-based catalysts, a large amount of research work has been devoted to using metal–support interaction in the past decade. It has been established that metal–oxide interactions can greatly impact the properties of noble metals (such as dispersion, particle size distribution, valence state, and thermal stability), thereby affecting catalytic performance [15, 16]. For instance, Song et al. investigated Pt supported on CeO2 catalysts modified with transition metal oxides and applied it to CO oxidation. They demonstrated that the electron-deficient Pt, due to the strong interaction between Pt and doping metal oxide, exhibited weaker CO adsorption strength [17]. Similarly, Tran et al. indicated that the dopants could enhance the interaction between the Pt nanoparticles and the catalyst support for iron-doped ZnO, resulting in improved catalytic activity [18]. Therefore, the introduction of transition metal oxides into Pt-based catalysts could be a feasible strategy to improve the catalytic oxidation of CO.

Niobium oxides (NbOx) are used widely in catalysis and in electrochromic and photoelectrochemical devices, due to the variable electrical conductivity, refractive index, and photoelectric properties produced by different structures [19, 20]. It is reported that the use of niobium oxides (Nb2O5) as a support can control oxygen vacancies by regulating the calcination atmosphere and time, which promotes the catalytic activity of CO oxidation, while oxygen activation on oxygen vacancy is more efficient for Pt/Nb2O5 catalysts [21]. In addition, Nb-based material is also widely applied as a solid acid catalyst. Zhang et al. proposed that Nb doping increased acid sites and weakened CO−Cu+ bond strength for CuOx/CeO2 catalysts [22]. Jardim et al. studied the preferential oxidation of CO in excess of H2 on Pt/CeO2–Nb2O5 catalysts and concluded that the presence of Nb in the supports inhibited their ability to adsorb CO [23].

Based on the above considerations, we fabricated a Pt-based catalyst on an Al2O3 support doped with NbOx, and Pt/Nb–Al2O3 was synthesized by a stepwise impregnation method. This study also compared the catalytic performance between Pt/Al2O3 with different transition metal oxide dopants. Combining a series of characterization and CO catalytic oxidation performance of Pt/Nb–Al2O3 with varying NbOx amounts would explore the influence of doping of NbOx on the physical and chemical properties of Pt/Al2O3 catalyst and the catalytic oxidation activity of CO.

2 Materials and Methods

2.1 Materials

Ammonium niobate(V) oxalate hydrate (Nb(HC2O4)5·nH2O, 99.99%), Ammonium vanadate (NH4VO3, 99.0%), Ammonium metatungstate hydrate ((NH4)6W12O39·xH2O, ≥ 85.0%), chloroplatinic acid hexahydrate (H2PtCl6·6H2O, 99.99%), and aluminum oxide (Al2O3, 99%) were purchased from Sigma-Aldrich. Ammonium molybdate 4H2O ((NH4)6Mo7O24·4H2O, extra pure, > 98.0%) was purchased from Daejung Chemicals & Metals Co., Ltd. To eliminate trace metals and impurities, commercial Al2O3 was carefully pretreated with a high-temperature calcination under 600 °C for 4 h. Unless otherwise specified, all chemicals are analytically pure.

2.2 Catalyst Preparation

2.2.1 Nb-Doped Al2O3 Carrier

Pretreated Al2O3 and Nb(HC2O4)5·nH2O were dissolved in 40 mL of deionized water and stirred in a water bath at 40 °C for 16 h, then the water was evaporated at 90 °C; subsequently, the dried powder was placed in a muffle furnace for 4 h at 450 °C, which aimed to remove impurity ions by high-temperature treatment to obtain Nb-doped Al2O3 carrier Nb–Al2O3. The Nb precursor dosage was changed to acquire a catalyst with various dopant amounts; Nb doping amounts were determined to be 1.20, 2.84, and 4.73 wt% using an inductively coupled plasma optical emission spectrometer (ICP-OES).

2.2.2 Nb-Doped Pt/Al2O3 Catalyst

Pt-based niobium alumina material was synthesized using the traditional wet-impregnation method. In brief, the as-prepared Nb–Al2O3 was dispersed in an aqueous solution containing hydrochloric acid, which was stirred for 4 h under ambient conditions. 265 mg of Pt precursor H2PtCl6·6H2O was used with 1.0 g of Nb–Al2O3 carrier powder, targeting a Pt loading of 1.0 wt%. The dry powder was transferred to a muffle furnace for 300 °C calcination, which was held for 4 h, and the high-temperature treatment tightly combined the platinum oxide and Nb–Al2O3. Finally, it was exposed to high-temperature reduction treatment in a hydrogen atmosphere, calcination at 200 °C in 3.9% H2/Ar for 2 h, and cooled down to room temperature to obtain a dark gray powder, which is the Nb-doped Pt/Al2O3 catalyst Pt/Nb–Al2O3. The real Pt loading and Nb doping amounts were determined to be 1.20 wt% and 4.73 wt% (seen in Table 1), respectively. For comparison, we prepared other transition metals as dopants utilizing a similar process as Pt/Nb–Al2O3, named with Pt/M–Al2O3 [M = vanadium (V), molybdenum (Mo), and tungsten (W)]. Similarly, Pt/Al2O3 without dopant was also prepared by wet impregnation.

Table 1 Characterization and catalytic activity of the Pt/Al2O3 and Pt/Nb–Al2O3 catalysts
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2.3 Characterization of the Catalysts

The size and morphology of the synthesized catalysts were assessed by transmission electron microscopy (TEM, Thermo Fisher, Talos F200X operated at 200 kV) accompanied by energy dispersive X-ray spectroscopy (EDS). The amount of Nb and Pt loading was measured by ICP-OES using a Thermal Scientific iCAP 6300. X-ray diffraction (XRD) patterns of the samples were recorded using a High-Resolution powder X-ray diffractometer (Rigaku, Smartlab at 45 kV and 200 mA) that scanned 2θ values between 10° and 80°. More structural characterization was obtained by the Raman spectroscopy technique employing LabRAM HR Evolution (Horiba, Japan) with a 514 nm laser source. X-ray photoelectron spectroscopy (XPS) was utilized to examine the chemical states of metal species on samples (Thermo VG Scientific, Sigma Probe). Binding energy calibration was based on C1s at 284.6 eV. XPSPeak 41 software was used for fitting the XPS peaks. The Shirley method was chosen for obtaining the background of spectra, and the Nb 3d spectra were fitted by the Gaussian–Lorentzian line function.

Metal dispersion on the samples was measured using CO pulse chemisorption (BELCAT-B; BEL Japan Inc.) with a stoichiometry factor of Pt:CO = 1:1. Pretreatment was done at 120 °C under H2 flow (50 sccm) for 1 h. 10% CO gas balanced with He was used as the gas pulse, and the measurement was carried out at 50 °C. H2 temperature-programmed reduction (H2-TPR) of the as-prepared samples was performed using a Micromeritics BELCAT-B (BEL Japan Inc.) instrument with a thermal conductivity detector under a 3.9% H2/Ar gas stream (50 mL/min), at a heating rate of 10 °C/min from 50 to 700 °C. Before the measurement was started, the fine-powder samples were treated in He (50 mL/min) at 450 °C for 1 h, followed by cooling at room temperature. The amount of H2 consumed for the reduction was measured with a thermal conductivity detector (TCD) and quantified using ChemMaster data analysis software. For CO–TPD experiments, the samples were reduced at 200 °C for 30 min using 3.9% H2/Ar at a flow rate of 30 mL/min. The samples were purged with He (30 mL/min) at the reduction temperature for 1 h. After cooling to room temperature, pulses (0.5 mL) of 10% CO/He were injected into a stream of He flowing through the samples until surface saturation was obtained. Then, the temperature was raised to 750 °C at the rate of 10 °C/min.

2.4 Evaluation of Catalyst Activity

The CO oxidation reaction was performed in a flow reactor, as described in previous works [24, 25]. The reactant gas composition contained CO and O2 with He used as the carrier gas (He:CO:O2 = 43:2:5), and the total gas flow rate was kept at 50 mL/min for all experiments which were controlled by mass flow controllers. Initially, 10 mg of the catalyst was diluted with 90 mg gamma-Al2O3 (97%) and then loaded into a tubular reactor. CO oxidation was carried out until 100% CO conversion was reached (at temperatures between 50 and 300 °C). Gas chromatography (DS Science) was used to analyze the mixed gas passing through the catalyst powder. The turnover frequency (TOF (s−1)) was determined based on the active Pt sites, which were measured using CO chemisorption [26]. In detail, the conversion of CO is kept below 20% to get the catalyst TOF value to ensure that the reaction is not affected by diffusion.

3 Results and Discussion

3.1 Characterization of the Synthesized Catalysts

Figure 1a displays the XRD patterns of a series of materials in the range of 10°–80°. Diffraction peaks corresponding to the crystal planes (111), (220), (311), (222), (400), (511), and (440) of γ-Al2O3 were observed at 19.4°, 31.9°, 37.5°, 39.3°, 45.7°, 60.5°, and 66.6°, respectively (PDF number: 50-0741) [27, 28]. For the Nb-doped Pt/Al2O3 materials, the same characteristic peaks were still present in the XRD patterns, indicating that the crystal structure of γ-Al2O3 remained unchanged after loading with metal oxides. Additionally, diffraction peaks at 46.2° were assigned to the (200) planes of Pt particles with a face-centered cubic (FCC) structure (PDF number: 04-0802) [29, 30]. Furthermore, no characteristic peaks corresponding to NbOx were detected in any of the patterns, possibly due to the uniform dispersion of Nb species on the alumina carrier surface or the low crystallinity and amorphous nature of Nb species [31,32,33,34]. Additionally, with an increase in the doping amount of Nb, a reduction in the intensity of the alumina characteristic peaks was observed, which might be attributed to the coverage of bulk NbOx or interactions between the NbOx species and the Al2O3 support [35, 36].

Fig. 1
figure 1

a XRD patterns and b Raman spectra of Pt/Al2O3 and Nb-doped catalysts

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In order to further verify the structural features of the catalyst, we conducted a Raman test, and the results were shown in Fig. 1b. All samples had two obvious bands at 310 and 440 cm−1 assigned to bayerite or gibbsite from the Al2O3 support, respectively. Notably, the peak at 440 cm−1 exhibited a lower signal over the Pt1.4/Nb2.8–Al2O3 sample, possibly because an appropriate dispersion of niobium species weakened the characteristic peak of the Al2O3 support. No strong characteristic narrow peaks were observed in the Raman spectra of a series of alumina samples, mainly due to the low polarizability of light atoms and the ionic character of the Al–O bonds or the presence of the cubic crystal symmetry nature of γ-Al2O3 [37,38,39]. Moreover, broad bands between 600 and 650 cm−1 were assigned to the ν2 transverse optical modes of Nb–O stretching, whereas the modes around the 900 cm−1 regions were ascribed to the high concentration of terminal surface Nb=O groups [40, 41]. Hence, Raman spectra were consistent with the XRD results, confirming highly dispersed Pt species and Nb2O5 phase loaded on the surface of γ-Al2O3.

TEM microscopy image and the corresponding particle size distributions of Pt1.1/Al2O3 and Pt/Nb–Al2O3 catalysts are shown in Fig. 2, and the elemental mapping of Pt and Nb are shown in Fig S1. It can be observed that the alumina catalyst exhibits a rod-shaped structure, with small dark spots presumed to be Pt particles dispersed on the catalyst surface. The inset HR-TEM image of Pt1.4/Nb2.8–Al2O3 shows a random Pt nanoparticle with a lattice fringe of 0.230 nm, which is attributed to the Pt (111) surface [42, 43]. Both the TEM and EDS data ascertained the successful deposition of Pt NPs on the synthesized Nb-doped Al2O3 supports. Additionally, a homogeneous distribution of Al and Nb could also be observed across the entire mapped area from the EDS mapping, indicating the effective doping of Nb into the Al2O3. For the Nb-doped catalysts, Pt particles display relatively narrow distributions between 0.3 and 2.4 nm with the majority of particles at about 1.5 nm. The mean particle sizes of material Pt particles can be further counted based on surface area weighted diameter. The mean Pt particle size of Pt1.4/Nb2.8–Al2O3 was 1.39 nm, similar to the particle size of Pt1.1/Al2O3 (1.31 nm) and smaller than that of Pt1.2/Nb4.7–Al2O3 (1.95 nm). Furthermore, the Nb elemental mapping image of Pt1.2/Nb4.7–Al2O3 is more obvious, and the Pt particle is rather vague in the TEM image compared with Pt1.4/Nb2.8–Al2O3, reflecting that excessive Nb content would influence the Pt dispersion.

Fig. 2
figure 2

TEM images of the synthesized: a, e Pt1.1/Al2O3, b, f Pt1.0/Nb1.2–Al2O3, c, g Pt1.4/Nb2.8–Al2O3, and d, h Pt1.2/Nb4.7–Al2O3 catalysts and their corresponding particle size distributions

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Redox properties of the catalysts were measured by the H2-TPR technique (Fig. 3a). The Al2O3 support does not show any distinct reduction peak in the temperature range of 50–700 °C, which agrees with the non-reducible nature of alumina [44, 45]. All catalysts show broad hydrogen uptake at 250 °C, the low-temperature reduction peak assigned to the reduction of weakly interacting Pt species, while a sharp contribution starts at a similar temperature of 200 °C. The subsequent flat peak that existed between 500 and 600 °C was attributed to Pt species strongly interacting with the support. These peaks shifted to lower temperatures with increasing Nb metal doping, which might be related to the smaller Pt particles, making the sample more reducible [46, 47]. The H2 consumption determined by deconvolution of peaks followed the trend Pt1.4/Nb2.8–Al2O3 < Pt1.2/Nb4.7–Al2O3 < Pt1.0/Nb1.2–Al2O3 < Pt1.1/Al2O3 (Table S1). These data suggest that Pt/Al2O3 had a slightly more oxidized Pt species than Pt/Nb–Al2O3, which consequently showed that Nb doping influenced the formation of oxidized Pt phases. The H2-TPR results indicated that the Nb dopant significantly enhances the reducibility of the Pt catalysts, particularly in high-temperature regions.

Fig. 3
figure 3

a H2-TPR profiles and b CO–TPD profiles of Pt/Al2O3 and Nb-doped catalysts

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Figure 3b shows the CO–TPD profile for the Pt-based catalysts, which could investigate CO species adsorption performance on the catalyst. There are two distinct CO desorption peaks for both the Nb-doped and non-doped samples when compared with the blank curve, which was obtained without CO gas. The initial peak is centered at low temperatures of 90 °C for Pt/Al2O3 and at 200 °C for Pt/Nb–Al2O3, which is attributed to the weakly adsorbed CO species. It was reported that these CO species are not active for CO oxidation, and they compete with O2 to adsorb on the active sites in the low-temperature region, resulting in poor reactive oxygen species and low activity of the samples [48, 49]. Obviously, the weakly adsorbed CO peak of Pt/Nb–Al2O3 has a larger area and starts at a higher temperature than that of Pt/Al2O3, which indicates that there are more available active sites for both CO species and O2 adsorbed on the Pt/Nb–Al2O3 catalysts. The second peak around 400–600 °C for all samples is assigned to the moderately adsorbed CO species on the catalysts [49,50,51]. Nb species might block Pt active sites for CO oxidation on Pt/Nb–Al2O3, leading to a slightly higher temperature shift when compared to non-doped Pt/Al2O3 catalysts for the high-temperature CO adsorption performance [52].

To further figure out the electronic interaction between Nb-doped Al2O3 support and Pt species, XPS was employed for the Pt-based catalysts, as shown in Fig. 4. In the Nb 3d regions (Fig. 4a), the peaks at binding energies 206.6 and 209.3 eV correspond to Nb4+ of 3d5/2 and 3d3/2 orbital with a spin–orbit splitting of 2.7 eV, whereas the other two peaks at 207.4 and 210.1 eV can be attributed to the 3d5/2 and 3d3/2 orbitals of Nb5+ [53,54,55,56]. The introduction of Nb into Pt/Al2O3 and the increase in Nb content for Pt/Nb–Al2O3 catalysts resulted in a positive shift in binding energy (the raw data can be seen in Fig S2 and peak position details are shown in Table S2), indicating there was a strong interaction between Nb-doped Al2O3 support and Pt metal particles. Meanwhile, the Nb4+/Nb5+ ratio (calculated based on the relative intensity of catalysts from the deconvolution of the XPS spectra) of Pt1.2/Nb4.7–Al2O3 (1.33) was lower than that of Nb4.7–Al2O3 (1.50) and Pt1.0/Nb1.2–Al2O3 (1.39), which further clarified that there was electron transfer from Nb-doped support to Pt metal particles due to the strong metal support interaction [57, 58]. Because of the partial overlapping signal between Pt 4f and Al 2p in the alumina support with the Al Kα anode target, we used the Pt 4d signals to distinctly identify Pt species (Fig. 4b). The Pt 4d5/2 and Pt 4d3/2 peaks can both be deconvoluted into two spin–orbit doublets (the raw data and peak position details are shown in Fig S3 and Table S3), reflecting the dominant population of Pt0 and the minor population of Pt2+, while the Pt 4d5/2 peaks at 314.0 and 317.0 eV were attributed to Pt0 and Pt2+, respectively [59,60,61]. The binding energy of the Pt 4d5/2 state of Pt0 was unaffected by the Nb addition when Pt/Al2O3 was compared with Pt/Nb–Al2O3, but the calculated ratio of Pt0/Pt2+ showed a slightly increased trend after Nb doping (as shown in Table S4), which meant a higher electron density of Pt atoms [62, 63]. Additionally, Pt1.4/Nb2.8–Al2O3 exhibited another peak at 307 eV, accounting for the electron-rich platinum species (Ptδ−).

Fig. 4
figure 4

XPS spectra of the Pt/Al2O3 and Pt/Nb–Al2O3 catalysts with different Nb contents in a the Nb 3d region, and b the Pt 4d region

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3.2 CO Oxidation Activity

The dependence of CO conversion on the reaction temperature for all the synthesized catalysts was depicted in Fig. S4. All catalysts exhibited comparable S-shaped conversion curves, wherein CO conversion augmented with elevated reaction temperatures. The experiments had very high repeatability with experimental errors of conversion rates below 10%, as confirmed by two separate runs of CO oxidation on the Pt/Al2O3 and Pt/NbOx–Al2O3 catalysts. The temperatures corresponding to 50% CO conversion (T50) of Pt/Nb–Al2O3, Pt/Al2O3, Pt/V–Al2O3, Pt/Mo–Al2O3, and Pt/W–Al2O3 were 216 °C, 227 °C, 239 °C, 245 °C, and 251 °C, respectively. Notably, CO displayed a swift rise in high-temperature regions, particularly beyond 210 °C. To further distinguish the difference between catalysts, we also compared several conversion rates around 210 °C, and the results are shown in Fig. 5. Figure 5a distinctly illustrates the inhibitory activity of catalysts doped with metals other than Nb in CO catalytic oxidation, when compared to the niobium-doped catalyst. From 214 to 220 °C, the conversion rate of Pt/Nb–Al2O3 rapidly escalated from 21.63 to 97.61%, while other catalysts exhibited only marginal increases in conversion rate. Between 220 and 225 °C, the conversion rate of Pt/Al2O3 exhibited rapid growth, whereas catalysts modified with other metals continued to display sluggish growth. To clarify the distinctions in catalytic reactions among various catalysts, H2-TPR was conducted as shown in Fig. S5a. The Nb-doped samples have similar reduction properties compared to their Nb-free counterpart, but a distinct difference is observed between other M-doped and non-doped catalysts. As for Pt/Mo–Al2O3 and Pt/W–Al2O3, the hydrogen consumption uptake is over 600 °C, mainly due to the evolution of new surface species, which could hardly be reduced because of the metal doping. Thus, it was speculated that the altered reducibility of the materials might be responsible for the poor catalytic activity of Pt/Mo–Al2O3 and Pt/W–Al2O3. For Pt/V–Al2O3, which maintained or even improved its reduction property, XPS was employed for further characterization, as depicted in Fig. S5b. Comparative analysis of Pt0/Pt2+ ratios between Pt/Nb–Al2O3 (1.48), Pt/V–Al2O3 (1.19), and Pt/Al2O3 (1.39) revealed that niobium doping enhanced the proportion of Pt0, whereas vanadium doping increased the proportion of Pt2+. Considering the catalytic activity outcomes and XPS analysis, implying that the electron effects between Pt and Nb species showed a conductive impact on CO catalytic oxidation [64, 65].

Fig. 5
figure 5

CO conversion at different reaction temperatures for a different metal oxide doped Pt/Al2O3 catalysts and b Nb-doped Pt/Al2O3 catalysts with different Nb content, c TOF calculated at different reaction temperatures and d Arrhenius plot of the Pt/Al2O3 and Pt/Nb–Al2O3 catalysts

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Figure 5b presents a comparison of CO conversion rates among catalysts with varying amounts of Nb doping (corresponding CO conversion as a function of temperature over Pt/Nb–Al2O3 with different Nb content is displayed in Fig.S3b). The activity sequence of Nb-doped Pt/Al2O3 catalysts was as follows: Pt1.4/Nb2.8–Al2O3 > Pt1.0/Nb1.2–Al2O3 > Pt1.2/Nb4.7–Al2O3. Catalytic activity improved while the Nb content increased from 1.20 to 2.84 wt%, as evidenced by a decrease in T50 from 215 °C to 210 °C. However, further escalation of Nb content leads to decreased activity, with T50 increasing once again. TEM and XPS analyses reveal that excessive Nb doping affects both Pt dispersion and the proportion of metallic platinum species. Consequently, CO oxidation activity diminishes. Pt1.4/Nb2.8–Al2O3 demonstrated optimal catalytic performance, which might be related to electron transfer and Pt/NbOx interface, underscoring the significance of the electron effect between Pt and Nb species in influencing CO oxidation activity. After CO oxidation reaction, Pt NPs in Pt1.4/Nb2.8–Al2O3 retained a size similar to the initial state (1.40 nm), showing the absence of sintering (Fig. S6). This indicates the stability of the catalyst in high-temperature oxidation reactions, highlighting the performance enhancement attributed to Nb doping.

Figure 5c shows TOFs calculated at different reaction temperatures. The TOF of Pt/Nb–Al2O3 at four temperatures always exhibited a similar trend with conversion rate: Pt1.4/Nb2.8–Al2O3 > Pt1.0/Nb1.2–Al2O3 > Pt1.2/Nb4.7–Al2O3. Figure 5d illustrates Arrhenius plots of ln (TOF) versus 1000/T for Pt1.1/Al2O3 and Pt/Nb–Al2O3 catalysts. Table 1 provides details on the catalysts' TOFs at 180 °C and the calculated activation energies (Ea) based on the Arrhenius equation. Variations in TOF values align with the trends observed in reaction rates, with Pt1.4/Nb2.8–Al2O3 exhibiting a higher TOF value of 3.12 s−1 and a lower Ea of 15.25 kcal/mol than other catalysts.

4 Conclusion

In this study, Pt-based catalysts doped with varying Nb contents were synthesized to investigate the influence of doping of niobium oxide on the catalytic activity of Pt/Al2O3 for CO oxidation. The influence of Nb doping on the structure and surface chemical composition of Pt/Al2O3 and Pt/Nb–Al2O3 catalysts was explored through systematic characterization. Combined XRD, Raman, and XPS analyses confirmed that Nb doping had no impact on the structure of alumina but significantly induced electron effect and the interface between Pt and Nb phase. Niobium doping promoted platinum reduction, leading to an increase in metallic platinum content, attributed to strong metal–support interactions between Pt and Nb-doped Al2O3 carriers. TEM and CO adsorption results also demonstrated that niobium doping favored platinum dispersion. In the catalytic CO oxidation reaction, Pt/Nb–Al2O3 was relatively dominant when compared with other metal-doped catalysts, owing to the more stable reducibility according to the H2-TPR results. Additionally, the CO–TPD showed the special CO adsorbed properties for Nb-doped catalysts which supplied more possibilities for oxygen adsorption in the low-temperature zone. Pt/Nb–Al2O3 catalyst with different Nb content exhibited a promoting effect relative to Pt/Al2O3, while Pt1.4/Nb2.8–Al2O3 also showed a superior T50 of 200 °C and TOF of 3.12 s−1 at 180 °C than Pt1.2/Nb4.7–Al2O3 catalyst with excessive Nb content. This finding emphasizes the potential of niobium oxide doping to enhance the catalytic activity of Pt-based catalysts for CO oxidation, offering new opportunities for optimizing catalytic processes in the field.