Pt / mo / al catalyst material, its preparation method and application

Abstract

The application discloses a Pt / Mo / Al catalyst material and a preparation method and application thereof, and belongs to the technical field of material preparation and propane catalytic combustion. The Pt / Al2O3 modified by MoO3 is used as a model catalyst, and is applied to a propane oxidation reaction. The Pt / Al2O3 catalyst modified by MoO3 has enhanced surface acidity and metal carrier interaction, and more metal Pt sites, which obviously promotes the propane oxidation reaction; and the application provides some ideas for designing a high-activity propane catalytic combustion catalyst in the future.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and propane catalytic combustion technology, specifically relating to a Pt / Mo / Al catalyst material, its preparation method, and its application. Background Technology

[0002] Emissions of volatile organic compounds (VOCs) pose a serious threat to human health and the ecological environment. With increasingly stringent pollution control regulations, achieving efficient VOC removal has become a major focus. Since the core of catalytic combustion technology is the catalyst, designing catalysts with excellent catalytic performance, high stability, and low cost has become a research hotspot in the field of environmental catalysis.

[0003] Typically, noble metals (such as Pt, Pd, Ru, and Rh) supported on various supports (e.g., Al₂O₃, TiO₂, CeO₂, and molecular sieves) are the most commonly used catalysts for the catalytic combustion of VOCs. To further improve supported noble metal catalysts, researchers have employed various strategies. Considering the crucial role of noble metal sites in the reaction, these strategies mainly focus on regulating the interaction between the noble metal state and the metal support. However, due to the complexity of catalyst preparation processes, strategies for regulating the noble metal state and metal support interaction are difficult to implement industrially. Therefore, researchers have conducted extensive studies on simple modifications to supported noble metal catalysts.

[0004] In recent years, researchers have generally agreed that surface acidity plays a crucial role in the catalytic oxidation of VOCs. Guided by this understanding, numerous studies have modified noble metal catalysts with acidic metal or inorganic acid groups through simple impregnation methods. These studies have found that WO3 modification can promote the reduction of Pt species and induce CH bond activation on Pt / Al2O3 catalysts in propane oxidation. In other words, acid modification may affect noble metal catalysts in the catalytic oxidation of propane. However, to date, a comprehensive discussion of the mechanism of this effect is still lacking, especially regarding traditional Pt group metal catalysts and commonly used acid modification strategies. Summary of the Invention

[0005] The first technical problem to be solved by this invention is to provide a Pt / Mo / Al catalyst material with excellent propane oxidation reaction performance. The second technical problem to be solved by this invention is to provide a method for preparing the Pt / Mo / Al catalyst material, which is simple and easy to implement, produces little waste by-product, and has a high product yield. The third technical problem to be solved by this invention is to provide an application of the Pt / Mo / Al catalyst material in propane combustion.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a Pt / Mo / Al catalyst material involves first preparing a Mo / Al support, and then loading Pt onto the support using an initial wet impregnation method to prepare a Pt / Mo / Al catalyst.

[0008] The preparation method of the Mo / Al support is as follows: (NH4)6Mo7O 24 • 4H2O and commercial γ-Al2O3 were dissolved in deionized water and stirred; the mixture was evaporated to dryness in an oil bath; then dried in an oven; and finally the solid was calcined.

[0009] The oil bath temperature is 90 ℃; the drying temperature is 110 ℃; and the drying time is 4 h.

[0010] The calcination temperature was 550 ℃, the heating rate was 5 ℃ / min, and the time was 4 h.

[0011] The Mo loading is 5~20 wt.%.

[0012] The Pt / Mo / Al catalyst is prepared by impregnating a Pt precursor salt onto a Mo / Al support and then calcining it to obtain a Pt / xMo / Al catalyst.

[0013] The Pt precursor is Pt(NO3)2; the Pt loading is 1 wt.%.

[0014] The calcination temperature is 550 ℃, the heating rate is 5 ℃ / min, and the calcination time is 2 h.

[0015] The Pt / Mo / Al catalyst material prepared by the method described above.

[0016] The application of the aforementioned Pt / Mo / Al catalyst material in propane combustion.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) This invention discloses a simple preparation process for MoO3 modified Pt / Al2O3 catalyst, which is simple and easy to operate, low in cost, low in waste by-products, and high in product yield;

[0019] (2) The low-loading Pt-based catalyst material prepared by the present invention has a Pt loading of ≤ 1 wt.%, which is lower than that of the materials reported by the previous researchers and has better catalytic performance;

[0020] (3) The present invention fully considers the influence of the acidity of the support surface on the interaction between metal supports and the state of noble metals, which can improve the propane combustion activity of Pt-based catalysts to a certain extent. Therefore, the Pt / Al2O3 catalyst material modified by simple MoO3 not only has good synthetic application value, but also has broad prospects in the field of practical catalytic applications. Attached Figure Description

[0021] Figure 1 XRD patterns of samples prepared for this invention; in the figures, (a) xMo / Al support; (b) Pt / xMo / Al;

[0022] Figure 2 The N2 adsorption-desorption isotherms of the samples prepared for this invention; in the figure, (a) xMo / Al support; (b) Pt / xMo / Al;

[0023] Figure 3 The pore size distribution diagram of the sample prepared according to the present invention is shown; in the figure, (a) xMo / Al support; (b) Pt / xMo / Al;

[0024] Figure 4 Raman spectra of samples prepared for this invention; in the figure, (a) xMo / Al support; (b) Pt / xMo / Al;

[0025] Figure 5 The in-situ infrared spectrum of CO adsorption in the sample prepared in this invention;

[0026] Figure 6 This is a CO temperature-programmed reduction curve of the sample prepared according to the present invention;

[0027] Figure 7 XPS images of samples prepared for this invention; in the images, (a) Pt 4d; (b) Mo 3d;

[0028] Figure 8 The accompanying diagram shows the NH3 temperature-programmed desorption process for preparing samples according to this invention.

[0029] Figure 9 The infrared spectrum of pyridine adsorption of the sample prepared in this invention;

[0030] Figure 10 This is a diagram showing the propane oxidation activity of the samples prepared in this invention;

[0031] Figure 11 This is a graph showing the stability of the prepared samples evaluated in the presence of 5 vol.% H2O according to the present invention. Detailed Implementation

[0032] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0033] Example 1

[0034] The method for preparing Mo / Al supports is as follows:

[0035] Weigh out 92 mg, 184 mg, 276 mg and 368 mg of (NH4)6Mo7O respectively. 24 • 4H2O and 1g of commercial γ-Al2O3 were dissolved in deionized water (Mo loadings of 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%, respectively) and stirred vigorously for 30 min; then, the mixture was evaporated to dryness in an oil bath at 90 °C; next, it was dried in an oven at 110 °C for 4 h; finally, the obtained solid was calcined at 550 °C for 4 h by increasing the temperature at 5 °C / min.

[0036] Example 2

[0037] The method for preparing Pt / Mo / Al catalysts is as follows:

[0038] 16.4 mg of Pt(NO3)2 precursor salt was weighed and impregnated with 1 g Mo / Al support (Pt loading was 1 wt.%). The temperature was increased to 550 °C at 5 °C / min and held for 2 h. The obtained Pt catalyst was denoted as Pt / xMo / Al.

[0039] The samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms, pore size distribution, Raman spectra, in-situ infrared spectroscopy of CO adsorption, CO temperature-programmed reduction, X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption, and pyridine adsorption infrared spectroscopy. The results are as follows:

[0040] Figure 1 The XRD patterns of the prepared samples show that when the MoO3 loading does not exceed 15 wt.%, no XRD peaks related to Mo species were observed on xMo / Al and Pt / xMo / Al, except for the XRD peak attributed to γ-Al2O3. When the MoO3 loading reaches 20 wt.%, an XRD peak attributed to β-MoO3 (111) (PDF#47-1081) appears. The γ-Al2O3 support (142 m3) used in this invention... 2 / g) MoO3 with no obvious agglomeration, with a maximum MoO3 loading of 15-20 wt.%. No crystalline Pt species were observed on any of the Pt / Al and Pt / xMo / Al catalysts, and the surface Pt was highly dispersed.

[0041] Figure 2 and Figure 3 The images show the adsorption-desorption isotherms and pore size distributions for xMo / Al and Pt / xMo / Al, respectively. Due to the high dispersion of Mo and Pt species on Pt / xMo / Al, the isotherm type and pore size of the γ-Al2O3 support remain almost unchanged after Mo and Pt deposition.

[0042] Figure 4 The Raman spectra of xMo / Al and Pt / xMo / Al are shown, where peaks α and β are related to the symmetric stretching vibration of Mo-O and the asymmetric stretching vibration of Mo=O, respectively. For xMo / Al, the peak area ratio (β / α) of peak β gradually decreases with increasing MoO3 loading, indicating that Mo=O bonds polymerize into Mo-O-Mo bonds and form polymolybdates. After Pt is deposited on xMo / Al, the value of β / α decreases further, indicating that the deposited Pt species interact with Mo=O, leading to the formation of Pt-O-Mo bonds and strong Pt-Mo interactions.

[0043] Figure 5 In-situ infrared spectra of CO adsorption in Pt / Al and Pt / Mo / Al. For Pt / Al, the values ​​at 2092 and 2037 cm⁻¹ are... -1 Two were observed at the location, respectively attributed to adsorption on Pt δ+ CO at the site (CO-PtO) x ) and adsorbed on Pt 0 CO at the site (CO-Pt) 0 CO-PtO x and CO-Pt 0 The coexistence of peaks indicates that the Pt species on Al2O3 are clusters or nanoparticles. After MoO3 modification, CO-Pt... 0 The enhanced peak intensity indicates that the Pt formed on Pt / xMo / Al is superior to that formed on Pt / Al. 0 More sites. Furthermore, when the MoO3 loading increases to 10 wt.% or higher, at 1816 cm⁻¹... -1 A new broad peak appeared, which is attributed to the adsorption of Pt on aggregated Pt species. 0 Bridged CO at the site indicates that more MoO3 leads to more surface Pt in Pt / xMo / Al. 0 Site.

[0044] Figure 6The results of CO temperature-programmed reduction tests on the prepared samples are shown. For Al2O3, no obvious CO consumption peak was observed in the range of 50-700 °C. After MoO3 deposition, a CO consumption peak was observed at 632 °C, which may be related to the reduction of MoO3. Two CO consumption peaks appeared on the CO temperature-programmed reduction curve of Pt / Al at 256 °C and 455 °C, which are attributed to the reduction of Pt-O and Pt-O-Al species. After MoO3 modification, the reduction temperature of Pt-O decreased (from 256 °C to 228 °C), indicating that Mo can promote the reduction of Pt-O. δ+ Species reduction. Compared to Pt / Al, the CO consumption peak intensity of Pt-O species on Pt / 15Mo / Al is relatively low, indicating that the average valence state of Pt species is low. Furthermore, the strong CO consumption peak induced by Pt-O-Mo reduction at 355 °C also confirms the formation of strong Pt-Mo interactions on Pt / 15Mo / Al.

[0045] Figure 7 The XPS test results for Pt / Al and Pt / Mo / Al are shown. For Pt 4d XPS, the peaks at approximately 314.3 and 331.3 eV are attributed to Pt. 0 The peaks at approximately 317.4 and 334.4 eV are attributed to Pt. 4+ Species. Based on the fitting analysis results, Pt / Al Pt 0 The species content was 20%. Pt / 15Mo / Al produced more metallic Pt species. 0 The proportion increased to 37%. Figure 7 b represents the Mo 3d XPS of 15Mo / Al and Pt / 15Mo / Al. The peaks centered at 236.4 eV (Mo 3d3 / 2) and 233.3 eV (Mo 3d5 / 2) on 15Mo / Al indicate that the Mo species on 15Mo / Al are mainly Mo 6+ Pt exists in the form of 3d XPS (0.2 eV) after deposition on 15Mo / Al, which causes the Mo 3d XPS to shift to a higher binding energy. This indicates that the Mo species can donate electrons to the Pt site through the Pt-O-Mo bond, thereby leading to the formation of electron-rich Pt species.

[0046] Figure 8 Results of temperature-programmed desorption of NH3 from Pt / Al and Pt / Mo / Al. Amount of NH3 adsorbed by 15Mo / Al (252 μmol NH3·g). cat . -1 It is almost Al2O3 (59 μmol NH3·g) cat . -1The concentration of NH3 was 5 times that of Al2O3, indicating that Mo modification can significantly improve the surface acidity of Al2O3. After Pt was deposited on Al2O3 and 15Mo / Al, the NH3 desorption peak was enhanced at low temperature (about 100 °C) and weakened at high temperature (about 400 °C). This may be related to the weak adsorption of NH3 at Pt sites and the strong interaction between Pt and Mo sites.

[0047] according to Figure 9 In the pyridine adsorption infrared results, for Al₂O₃ and Pt / Al, the surface acid sites are predominantly Lewis acids. However, for 15Mo / Al and Pt / 15Mo / Al, infrared peaks at 1489 cm⁻¹, clearly attributable to pyridine adsorption on Brønsted acid sites, are observed, and these peaks are significantly higher than those at Al₂O₃ and Pt / Al. -1 The peak intensity also increased, indicating that the introduction of MoO3 led to the formation of abundant Brønsted acid sites on Al2O3.

[0048] Example 3

[0049] The Pt / Mo / Al catalysts prepared in Examples 1 and 2 were applied to the propane catalytic combustion reaction. The activity of the propane catalytic combustion reaction was evaluated in a fixed-bed quartz tube reactor. The specific steps are as follows:

[0050] A certain amount of catalyst (40-60 mesh) was mixed with SiC (mass ratio of catalyst to SiC 1:5) and loaded into a quartz tube reactor. The mixture was pretreated at 300 °C with high-purity air (30 mL / min) for 1 h. The catalyst dosage was 60 mg, and the reaction gas (100 mL / min) consisted of 4000 ppm C3H8 and 5% O2, with Ar as the equilibrium gas. The WHSV was 100,000 mL·g. cat -1 ·h -1 The propane conversion rate in the propane oxidation reaction is calculated using the following formula:

[0051]

[0052] Figure 10 This is a diagram showing the propane combustion activity of the prepared catalyst. The results indicate that Mo doping significantly improves the catalytic performance of Pt / Al in the propane oxidation reaction, and the optimal MoO3 loading for Pt / xMo / Al is 15 wt.% (T). 50 = 242 ℃). This phenomenon shows that surface MoO3 modification affects the surface acidity of Pt / Al2O3 catalyst, the interaction between the metal support and the state of Pt species, thereby affecting the propane combustion activity.

[0053] Figure 11The stability of the prepared samples was evaluated in the presence of 5 vol.% H2O. The results showed that the introduction of 5 vol.% H2O deactivated the Pt / Al and Pt / 15Mo / Al catalysts in propane oxidation. However, the stability remained unchanged with respect to the To of Pt / Al. 50 Compared to (25 ℃), Pt / 15Mo / Al has a higher temperature range. 50 The increase was relatively small, indicating that Mo modification can enhance the H2O tolerance of Pt / Al catalysts.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Pt / Mo / Al catalyst material, characterized in that, Includes the following steps: (1) The method for preparing Mo / Al support is as follows: Weigh out 276 mg of (NH4)6Mo7O 24 • 4H2O and 1g of commercial γ-Al2O3 were dissolved in deionized water, and the Mo species loading was 15wt.% based on the mass of metallic Mo element. The mixture was stirred vigorously for 30min. Then, it was evaporated to dryness in an oil bath at 90℃. Next, it was placed in an oven and dried at 110℃ for 4h. Finally, the obtained solid was calcined at 550℃ for 4h by increasing the temperature at 5℃ / min. (2) The method for preparing Pt / Mo / Al catalyst is as follows: 16.4 mg of Pt(NO3)2 precursor salt was weighed and impregnated with 1 g of Mo / Al support. The Pt loading was 1 wt.%, and the temperature was increased to 550 °C at 5 °C / min and held for 2 h. The obtained Pt catalyst was a MoO3 modified Pt / Al2O3 catalyst material, denoted as Pt / 15Mo / Al.

2. The Pt / Mo / Al catalyst material prepared by the method according to claim 1.

3. The application of the Pt / Mo / Al catalyst material according to claim 2 in propane combustion.

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