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Article

Room-Temperature Complete Oxidation of Formaldehyde over Lactic Acid-Modified HZSM-5-Supported Pt Catalyst

by
Tongtong Zhang
,
Sijia Wang
,
Xingyuan Li
,
Yupeng Du
,
Jiajun Hu
,
Shi Jiang
* and
Yu Guo
*
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 211816, China
*
Authors to whom correspondence should be addressed.
Processes 2025, 13(5), 1440; https://doi.org/10.3390/pr13051440
Submission received: 26 March 2025 / Revised: 5 May 2025 / Accepted: 7 May 2025 / Published: 8 May 2025
(This article belongs to the Special Issue Design and Performance Optimization of Heterogeneous Catalysts)
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Abstract

:
Room-temperature complete oxidation of formaldehyde (HCHO) is an important orientation of research programs, yet challenges remain. The development of efficient catalysts with high activity and excellent stability is of great significance for such practical application. Inspired by this whole catalytic process, we, therefore, chose HZSM-5 zeolite with abundant acidic sites as catalyst support and lactic acid (LA) as modifier to regulate the properties. The use of LA simultaneously enhances the hydroxyls density and increases the dispersion of Pt nanoparticles, which are better than the reference catalyst prepared via direct wetness impregnation method. Most satisfying of all, the lactic acid-modified HZSM-5-supported Pt catalyst demonstrates a remarkable reaction performance for room-temperature HCHO oxidation at a high concentration HCHO of 80 ppm and a large space velocity of 360,000 mL/g/h (especially with a low Pt loading of 0.5%). In addition, a 120 h test further confirms the favorable stability of the designed catalyst. This pre-modified strategy using organic acid might provide potential approach in the construction of efficient zeolite-supported catalysts.

Graphical Abstract

1. Introduction

Formaldehyde (HCHO) is one of the common chemicals used in some household products or building materials, such as glues, adhesives, dishwashing liquids, coatings, fabric softener, and so on [1,2,3,4]. Not only that, preservatives used in some medicines and cosmetics may also contain formaldehyde. Despite its various utility in human life, there are also negative effects on our health both in the short term and long term (even ppm level). Therefore, numerous efforts have been devoted to developing efficient methods for eliminating indoor formaldehyde, mainly including adsorption [5,6], photocatalysis by exposure to ultraviolet light [7], plasma decomposition [8], and catalytic oxidation over heterogeneous catalysts [9]. Among them, catalytic oxidation of HCHO at room temperature (RT) is identified as a convincible and environmentally friendly protocol, producing water and carbon dioxide as the harmless products [10,11,12,13]. However, as things stand at present, the highly effective and promising systems usually involve supported noble metal catalysts with a relatively high metal loading (>1%). Thus, the current supply mode of the market poses a severe challenge to the development of a low-cost catalyst with high activity especially at room temperature [14,15,16,17].
In the previous studies, the construction of various supported noble metal catalysts has enabled their reliable catalytic activities in HCHO oxidation, e.g., Pd/CeO2 [18], Pd/TiO2 [19], Pt/Al2O3 [20], Pt/TiO2 [21], Pt/CeO2 [22], and Pt/C@MnO2 [23]. In general, Pt nanoparticles (NPs) immobilized onto solid supports are the most frequently used with outstanding catalytic performance [24,25,26,27]. Nevertheless, high metal loading (>1%) is commonly involved and leads to low atom efficiency of these expensive noble metal species. The smaller NPs facilitate improving the metal utilization and activity, but the increased surface energy will easily increase the risk of agglomeration and deactivation [28,29]. Based on these issues, a wide range of supports is being investigated for the modulation of the electronic and geometric state of Pt NPs in order to improve the catalytic performance in the RT-catalyzed HCHO oxidation. For example, our previous studies demonstrated a Na-doped Pt/Al2O3 catalyst, in which the both hydroxyl groups and Pt dispersion were indispensable parameters for the synergistically catalytic combustion of HCHO at RT [30]. Ji and co-authors reported that the Pt/ZSM-5 catalyst with proper amount of sodium hydroxide modification could enhance HCHO adsorption/storage capacity and intermediates oxidization rate through ameliorating pore structure and surface hydroxyl groups at 30 °C [31]. Right after that, they developed a Pt-Ni/ZSM-5 catalyst with enhanced nearby hydroxyl density around the Pt active sites with a better HCHO removing efficiency of ~90% at 30 °C and a 100 h stable performance [32]. All of these displayed that the activity of Pt-based catalysts could be regulated by the nature of the support to ensure the performance in catalytic oxidation of HCHO. However, the modification with alkalis or metal species usually is not controllable after all, which may result in some irreversible problems, such as deep defect of the original porous structure, sodium/potassium residual and even environmental issues.
ZSM-5 zeolite (Zeolite Socony Mobil No. 5) of the MFI structural type (Mobile Five) has high hydrothermal stability, high specific surface area, excellent shape selective catalytic effect, wide range of silicon aluminum ratio variation, unique surface acidity, and low carbon deposition. It is precisely based on the above advantages that ZSM-5 zeolite has been widely applied in various fields such as refining industry, fine chemical industry, and environmental protection. Therefore, HZSM-5 with abundant acid sites and a well-arranged pore structure was selected as the catalyst support in this work. In comparison with alkalis treatment, zeolites could be modified by strong acids (such as hydrochloric, nitric acid and phosphoric acid) to create more quantified physicochemical properties for various specific applications. Nevertheless, too strong acidity easily leads to great changes in the skeleton, especially in the aspects of Al atom leaching and pore channel collapse. Lactic acid (LA) as a mild organic acid could be used to tailor the compositional and textural properties of zeolite in a more controlled way without affecting intrinsic characteristics of skeleton. Thus, in this study, LA was used as an efficient modifier and a series of modified HZSM-5 (HZ) zeolite-supported Pt catalysts with a low Pt loading of 0.5% were first constructed for complete oxidation of HCHO at room temperature. To our delight, the lactic acid-modified HZSM-5-supported Pt catalyst exhibited a significantly improved catalytic performance in comparison to the reference catalyst prepared via direct wetness impregnation method. A 120 h continuous test further confirmed its excellent catalytic activity and stability. With the systematic characterizations, it was found that the characteristic of the mild organic acid could not only increase the hydroxyls density on the support but also improve Pt dispersion indirectly.

2. Materials and Methods

2.1. Materials

HZSM-5 zeolite was purchased from Nankai University Catalyst Co., Ltd., Nankai, China. Chloroplatinic acid hexahydrate (H2PtCl6, Pt ≥ 37.5%) was purchased from Macklin Chemical. Lactic acid was purchased from Aladdin Chemical, Shanghai, China. Other chemicals and reagents were also commercially available and purchased from Aladdin Chemical without further purification.

2.2. Catalyst Synthesis

HZSM-5 zeolite (2 g; Nankai University Catalyst Co., Ltd.) with a SiO2/Al2O3 molar ratio of 20 was calcined at 500 °C for 3 h with a heating ramp of 2 °C/min. The obtained sample was dipped in lactic acid (LA) solutions (20 mL) of different concentrations (3%, 8%, 15%, and 20% based on the amount of solid) at 80 °C for 6 h, followed by centrifugation. Each of the resulting solids were impregnated with 0.01 g of H2PtCl6 dissolved in 10 mL of water at 25 °C for 4 h, and dried at 70 °C to prepare the supported Pt catalysts (0.5% Pt loading, in weight). Finally, the catalysts were dried at 110 °C for 12 h and then calcined at 500 °C for 3 h in static air to remove the rested organic acid. LA-modified HZSM-5 zeolite supported Pt catalysts were denoted as Pt/HZ-x% LA, where x represents the amount of LA in weight percentage on the initial solid.

2.3. Catalyst Characterization

The X-ray powder diffraction (XRD) patterns were collected on a Rigaku SmartLab XRD (Rigaku, Japan) using a Cu Kα source and at a scanning rate of 1°/min radiation from 5° to 50°. The Pt, Al, and Si concentration in all samples was conducted using SWITZERLAND ARL9800 (Switzerland) X-ray fluorescence spectrometer (XRF). The structural parameters, pore size distributions, and N2 adsorption–desorption isotherms of the samples were measured at liquid nitrogen temperature using a Belsorp Mini instrument (Ankersmid, Netherlands), and the samples were pre-treated under a vacuum at 300 °C for 3 h. Fourier transform infrared (FT-IR) spectra were collected on a Thermo Nicolet is5 infrared spectrometer (Thermo Fisher, Waltham, MA, USA). KBr powder was used for tablet pressing, and the range of 400–4000 cm−1 was scanned at room temperature to collect corresponding data. Tensor 27 (Bruker, Germany) was used for pyridine infrared (Py-IR) analysis. 0.03 g of the sample was pressed and placed in the in situ cell. Each was vacuumized at 200 °C for 6 h, and the pyridine was adsorbed at room temperature until the adsorption amount reached stability. The pyridine infrared wavelength used is 1400–1700 cm−1. The Pt dispersion was based on the carbon monoxide (CO) chemisorption (pulse titration) measurement (ChemBET 3000, Quantachrome Instruments, Co., Ltd., USA), as reported in our previous study [30]. The adsorption and desorption of ammonia (NH3-TPD) were performed on a JAPAN BELCAT-B Analyzer instrument (Japan). The element composition and the Pt surface chemical state were analyzed by X-ray photoelectron spectroscopy (XPS), which was carried out on a Kratos AXIS Supra (Japan) X-ray photoelectron spectrometer equipped with Al Kα radiation. A 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectrum was collected by an AVANCE Ⅲ HD 400 MHZ (Bruker) spectrometer.

3. Results

3.1. Catalyst Characterization

A Pt/HZ-x% LA catalyst was prepared through a wetness impregnation method, where the HZSM-5 zeolite was treated in a lactic acid solution, followed by centrifugation, and then it was impregnated into H2PtCl6 solution. X-ray diffraction (XRD) patterns of HZSM-5 (HZ) and the Pt/HZ-x% LA series (x = 0, 3, 8, 15, and 20) displayed typical peaks (2θ = 7.8°, 8.7°, 23.2°, 24°, and 24.4°) assignable to the MFI topology with negligible signals for impurities, indicating that the pre-treatment with LA did not disturb the original crystalline structure of MFI (Figure 1) [33]. Compared with the simple HZSM-5 zeolite-supported Pt catalyst (Pt/HZ), the almost disappearance of the sharp diffraction peaks for the metallic Pt0 (2θ = 40°) between Pt/HZ-3% LA and Pt/HZ-8% LA demonstrated the increased metal dispersion, which implied the effectiveness of LA in the pre-treatment of HZSM-5 [31]. Nevertheless, with the increase in LA content, obvious traces of characteristic peaks to metallic platinum gradually appear (Pt/HZ-15% LA and Pt/HZ-20% LA).
As shown in Figure S1, the porosity information of HZ and the Pt/HZ-x% LA series displayed typical Ⅰ + Ⅳ isotherms with a slow uptake at a low relative pressure and a continuously increasing uptake at a higher relative pressure, suggestive of micro-mesoporous materials [34]. The BET surface area, SiO2/Al2O3 mole ratio, and Pt dispersion are shown in Table 1. It was presented that Pt/HZ has a surface area of 396 m2/g and a pore volume of 0.17 cm3/g, which is quite similar to that of simple HZ (396 m2/g and 0.17 cm3/g). In addition, the Pt/HZ-x% LA series have surface areas of 371–375 m2/g and pore volumes of 0.16–0.17 cm3/g, which are slightly smaller than that of HZ. The porosity of these LA-treated Pt-based catalysts was close to that of their parent HZ zeolite support, in line with the result of the above XRD patterns. Meanwhile, the molar ratio of SiO2 to Al2O3 in the final Pt/HZ-x% LA series determined by the XRF analysis was kept almost the same with the original support form. In contrast, the dispersion of HZ-supported 0.5% platinum catalyst (Pt/HZ), determined by CO titration, exhibited relatively low dispersion of 12.3% in the absence of any additives. The addition of appropriate amount of LA promoted the dispersion to 13.3% for Pt/HZ-3% LA and 35.6% for Pt/HZ-8% LA. With the increase in LA concentration, the metal dispersion offered a downward trend, indicating that more LA brought some changes in the intrinsic morphology of HZ support and weakened the stabilization towards Pt NPs.
The FTIR absorption spectra of HZ and the Pt/HZ-x% LA series exhibited the featured peaks at 452, 545, 796, 1095, and 1224 cm−1, which belong to the identified characteristic of ZSM-5 framework (Figure 2a) [35]. This is well in agreement with the above XRD results. Noticeably, the absorption band around 545 cm−1 represents the structural vibration of the double five-membered rings in the MFI structure, and the band located at 1095 cm−1 is designated as the internal vibration of the TO4 tetrahedra. The strong and broad signal at 3475 cm−1 could be attributed to the adsorbed water on the surface. Another band located at 3690 cm−1 generally corresponds to the isolated silanol (Si-OH) groups in the zeolite framework [36]. It is known that the existence of moderate hydroxyls density is beneficial for the high efficiency in catalytic oxidation of HCHO [37,38]. However, in the absence of LA or in the presence of an excess of LA, the relative intensity of the characteristic peaks at 3690 cm−1 had an obvious decrease. With the optimization of LA content, Pt/HZ-8% LA catalyst matches well in this respect, giving great potential for promoting complete oxidation of HCHO under relatively low humidity.
The acid properties of HZ and the Pt/HZ-x% LA series samples were investigated by NH3-TPD and FTIR spectroscopy of pyridine adsorption. As shown in Figure S2, two different peaks at 150–250 °C and 300–450 °C were observed, which were ascribed to the desorption of ammonia on weak/moderate and strong acid sites, respectively. Significantly, the acid strength of the Pt/HZ-x% LA samples was enhanced versus HZ and Pt/HZ due to the potential in situ reintegration of the Si-Al framework. The nature of acid sites of all samples was further distinguished via Py-FTIR analysis (Figure 2b). The parent zeolite HZSM-5 showed the classical set of bands at 1450 cm−1 and 1540 cm−1, which were assigned to Lewis acid sites (L) and Brønsted acid sites (B), respectively [39,40]. There were no obvious changes in the number of L and B acid sites when Pt species were loaded on the HZ support. It is interesting to note that the introduction of 3% and 8% LA promotes the increase in the number of L acid sites, which is partly consistent with the situation in NH3-TPD results. Even if the LA amount was increased to 15%, it did not lead to complete changes in the nature of L and B acid sites.
For all the four samples, the high-resolution O 1s XPS spectra (Figure S3) were deconvoluted into lattice oxygen (Olat, ~532.0 eV), surface oxygen (Osur, ~531.0 eV), and physiosorbed water (Oads, ~530.6 eV) [41,42,43]. The observed O 1s binding energy at around 531.0 eV could be attributed to the surface hydroxyl. Based on the corresponding areas of XPS fitted peaks, the proportion of Osur in the total surface oxygen (Ototal) in each sample is calculated to evaluate the content of surface hydroxyl density. With the increase in LA amount, the ratio of Osur/Ototal first increases, reaching a maximum value of 59.90% over Pt/HZ-8% LA and then decreases with excessive amounts (Table 1).
To clarify the changes in the microenvironment of Al atoms, 27Al MAS NMR analysis of the Pt/HZ-x% LA series was carried out by comparison with the initial support HZSM-5 (Figure 3). All the samples exhibited two chemical shifts around 55 ppm and 0 ppm, representing the tetrahedral-coordinated Al (T-Al) species and extra-framework octahedral-coordinated Al species (O-Al) in the zeolite framework, respectively [39,44,45]. It could be obviously observed that, with the increase in LA treatment capacity, the intensity of T-Al signal was decreasing along with the trend of moving to the position of O-Al. The shift in T-Al peak position is probably related to the change in Al coordination structure. This indicates that the addition of LA more or less causes the shedding of a small number of framework Al species followed by in situ redispersion.

3.2. Catalytic Oxidation of HCHO

The catalytic activity for the RT HCHO oxidation was determined under 80 ppm HCHO, 360,000 mL/g/h of space velocity, and relatively dry conditions (RH = 10%). Ahead of the test, all the samples were pre-treated in flowing H2 at 400 °C for 4 h. Figure 4 showed the activity of the Pt/Na-ZSM-5 sample (sodium type ZSM-5) and Pt/H-ZSM-5 in the oxidation of HCHO at RT in order to investigate the influence of the support. Both catalysts were prepared through a traditional wet impregnation method. For the Pt/Na-ZSM-5 sample, a conversion of 15% for HCHO was obtained within 5 h. In the case of HZSM-5-supported Pt catalyst (Pt/HZ), the catalytic activity was slightly better (around 25% HCHO conversion). This result implies that the presence of acid sites can serve as a positive role to facilitate the adsorption and activation of the aldehyde group, giving a better RT activity.
Accordingly, the HZSM-5 support was modified with different amounts of LA (HZ-x% LA), and a series of HZ-x% LA-supported Pt catalysts (Pt/HZ-x% LA) were further systematically evaluated for this reaction (Figure 5). Pt/HZ-3% LA displayed much higher HCHO conversion in comparison to the Pt/HZ at 20 h, almost triple the previous maximum (75% vs. 25%). With the initial LA loading increasing to 8%, a nearly complete conversion of formaldehyde was observed over the Pt/HZ-8% LA catalyst within 20 h. This representative performance gives potential application in the room-temperature removal of indoor formaldehyde in our daily life. Nevertheless, after a further increase in the amount of LA usage on the support, a negative performance in HCHO oxidation appeared, and only an average 65% and 40% conversion of formaldehyde was achieved in the presence of Pt/HZ-15% LA and Pt/HZ-20% LA, respectively. In addition, the influence of a different space velocity over the Pt/HZ-8% LA catalyst was evaluated by using humid HCHO + O2 + N2 flow gas (80 ppm HCHO, 20% O2, relative humidity (RH) = 10%) under the SV of 180,000 and 540,000 mL/g/h (Figure S4). Rapid and complete HCHO removal was observed under the SV of 180,000 mL/g/h and the activity was stably maintained within 20 h, which was better than the case of 360,000 mL/g/h. Further increasing the SV to 540,000 mL/g/h caused a continuous decline in HCHO conversion, but the removal ratio was still over 80% after 20 h. All of these visualize the superiority of Pt/HZ-8% LA in room temperature HCHO oxidation, which is especially suitable for the situation of dramatic volatile SV, such as indoor air purification.
Moreover, a long-term activity test of HCHO oxidation was carried out to evaluate the stability of the idol catalyst (Pt/HZ-8% LA), which is more meaningful for practical application, especially for noble metal catalysts. When RH was adjusted to 60%, comparable to the humidity conditions of the real environment, the Pt/HZ-8% LA catalyst achieved the complete oxidation of HCHO at room temperature, and no obvious catalyst deactivation was observed within the tested 120 h (Figure 6).

4. Discussion

In the present research and our previous studies, it has been reported that several influencing parameters could affect the RT oxidation activity of HCHO, and the influences of metal dispersion, acidic sites, and surface hydroxyl groups are most prominent [30,31,32]. In general, the process of HCHO oxidation via supported platinum catalysts mainly includes the generation of formate species and transformation of formate species into CO2/H2O. In the case of the reported Al-rich Beta zeolite-supported platinum sample (Pt/HBeta-SDS-4), the acidic sites are beneficial for the generation of HCOOH from HCHO [46]. More than that, the existence of surface hydroxyls supports a positive impact on the adsorption of HCHO [32]. Notably, the decomposition efficiency of the formate species is closely related to the Pt dispersion, which is often responsible for the oxygen adsorption capacity and is most likely a rate-determining step in the whole process [37,38].
To understand the promotion effect of lactic acid as a modifier, we systematically investigated the relationship between HCHO conversion after 10 h on time of stream and Pt dispersion, Osur/OTotal, acidic sites, and other factors. Nevertheless, this feature is quite different from the results obtained from this zeolite-supported Pt catalyst system, where the replacement of sodium cation with protons displayed an enhanced activity. This phenomenon is most probably assignable to the increased activation ability of oxygenates via acidic sites. Figure 7 correlates the conversion of HCHO with the Pt dispersion and the Osur/OTotal. Overall, with the increase in lactic acid, the conversion of HCHO presented a tendency of volcanic type change, while at the same time contributing to the almost similar situation of that of Pt dispersion and the Osur/OTotal. The treatment with a low lactic acid concentration was able to present homogeneously inside the channels of ZSM-5 zeolite and had little influence on the morphology of the support, which was evidenced by the 27Al MAS NMR analysis. As a result, due to the interaction between the acid and aluminum, the species at unsaturated sites fell off, leading to additional hydroxyls. This information is well in line with that of the significant enhanced HCHO conversion (from 25% to 75%), where the platinum dispersion has only increased a little, demonstrating the indispensable role of hydroxyls. The satisfactory performance in HCHO oxidation resulted from the comprehensive cooperation between a high hydroxyls density (Osur/OTotal) and well-dispersed Pt nanoparticles, which are closely related to a moderate lactic acid usage. In contrast, hyper-concentrated lactic acid usually diffuses faster, resulting in not only a higher adsorption equilibrium value but also irreversible zeolite structural change. Therefore, the spatial constraint effect of lactic acid and more extra-framework octahedral-coordinated Al species brought decreased Pt dispersion and hydroxyls density, respectively. Even so, the supposed poorer distribution was still better than that of simple Pt/HZ and finally gave an HCHO conversion of 65%, indicating that the higher dispersion degree is beneficial for a larger oxygen adsorption capacity along with enhanced catalytic activity.
In addition, it is noteworthy that the increase in RH can significantly improve the catalytic activity and stability of formaldehyde oxidation at room temperature (Figure 6). This mainly attributes to the generation of greater hydroxyl density on the catalyst surface, promoting the decomposition of the formate species. Based on the results above and our previous investigation [30,31,32], it is proposed that both the surface hydroxyls density and the dispersion of Pt nanoparticles allow good cooperation in the room-temperature complete oxidation of HCHO over the zeolite-supported Pt catalyst.
Based on the results above, the probable catalytic pathway for HCHO oxidation over the Pt/HZ-8% LA catalyst was put forward and proposed in Figure 8. Firstly, the molecule HCHO was adsorbed on the catalyst, which was assisted by the hydrogen bonding interaction with the surface hydroxy group (Step I). At the same time, oxygen molecules were active on the Pt NPs, giving two surface active oxygen atoms (Step I). Then, the intermediate was generated between the active oxygen atom and the adsorbed HCHO by the effect of electrophilic attacking (Step II). Subsequently, the intermediate reacted with the surface hydroxy group and transformed into the HCOO− species (Step III). Finally, the HCOO− species reacted with the surface hydroxy group and then decomposed into CO2 and H2O (Step IV). In general, this is the synergy between Pt NPs and the surface hydroxy group, as shown in Figure 7.

5. Conclusions

In summary, modification of the HZSM-5 zeolite by treatment with organic acid (LA) under mild conditions brought enhanced hydroxyl density and indirectly gave improved Pt dispersion. The LA-modified HZSM-5-supported Pt catalyst displayed significantly promising catalytic activity when it was subjected to the HCHO RT oxidation reaction at a high HCHO concentration of 80 ppm, a large space velocity of 360,000 mL/g/h, and a low relative humidity of 10%. The major contribution in this strategy is to manipulate the hydroxyls density–Pt dispersion trade-off relationship through appropriate LA usage, where such a synergistic effect gives an enhancement of catalytic activity and stability. In short, this finding might offer an effective way to highlight its application potentials of constructing efficient supported noble metal catalysts for the clean-up of air pollutants.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pr13051440/s1, Figure S1: N2 adsorption–desorption isotherms of HZ and the Pt/HZ-x%LA catalysts; Figure S2: NH3-TPD profiles of HZ and the Pt/HZ-x%LA catalysts; Figure S3: O 1S XPS spectra of the Pt/HZ-x%LA catalysts; Figure S4: Time-resolved conversion in the HCHO oxidation over Pt/HZ-8% LA catalyst at different SV. Reaction condition: Room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, RH = 10%, and N2 as the balance gas.

Author Contributions

Writing—original draft preparation, T.Z.; writing—review and editing, S.W.; formal analysis, X.L.; validation, T.Z. and J.H.; data curation, Y.D. and J.H.; supervision, S.J. and Y.G.; project administration, S.J. and Y.G.; funding acquisition, S.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, grant number 22108116.

Data Availability Statement

The data presented in this study are available on request from the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Wide-angle powder XRD patterns of HZ sample and the series of Pt/HZ-x% LA catalysts, along with magnified patterns around 40°.
Figure 1. Wide-angle powder XRD patterns of HZ sample and the series of Pt/HZ-x% LA catalysts, along with magnified patterns around 40°.
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Figure 2. (a) FT-IR spectra of the HZ sample and the series of Pt/HZ-x% LA catalysts, along with magnified range from 3200 cm−1 to 3900 cm−1 at room temperature and (b) IR spectra of pyridine adsorbed on the HZ sample and the series of Pt/HZ-x% LA catalysts at 200 °C.
Figure 2. (a) FT-IR spectra of the HZ sample and the series of Pt/HZ-x% LA catalysts, along with magnified range from 3200 cm−1 to 3900 cm−1 at room temperature and (b) IR spectra of pyridine adsorbed on the HZ sample and the series of Pt/HZ-x% LA catalysts at 200 °C.
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Figure 3. 27Al MAS NMR spectra of HZ and the Pt/HZ-x% LA catalysts.
Figure 3. 27Al MAS NMR spectra of HZ and the Pt/HZ-x% LA catalysts.
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Figure 4. A comparison of the catalytic performance for the oxidation of HCHO over Pt/Na-ZSM-5 and Pt/H-ZSM-5 (the data were collected after 5 h). Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, Space Velocity (SV) of 360,000 mL/g/h, Relative Humidity (RH) = 10%, and N2 as the balance gas.
Figure 4. A comparison of the catalytic performance for the oxidation of HCHO over Pt/Na-ZSM-5 and Pt/H-ZSM-5 (the data were collected after 5 h). Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, Space Velocity (SV) of 360,000 mL/g/h, Relative Humidity (RH) = 10%, and N2 as the balance gas.
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Figure 5. Dependence of HCHO conversion on reaction time in HCHO oxidation over different catalysts. Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, SV of 360,000 mL/g/h, RH = 10%, and N2 as the balance gas.
Figure 5. Dependence of HCHO conversion on reaction time in HCHO oxidation over different catalysts. Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, SV of 360,000 mL/g/h, RH = 10%, and N2 as the balance gas.
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Figure 6. Durability evaluation of Pt/HZ-8% LA for HCHO oxidation. Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, SV of 360,000 mL/g/h, RH = 60%, and N2 as the balance gas.
Figure 6. Durability evaluation of Pt/HZ-8% LA for HCHO oxidation. Reaction conditions: room temperature of 25 °C, HCHO concentration of 80 ppm, O2 20%, flow rate of 300 mL/min, SV of 360,000 mL/g/h, RH = 60%, and N2 as the balance gas.
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Figure 7. Dependence of Pt dispersion and hydroxyls density for HCHO conversion at 10 h on lactic acid treatment capacity of HZSM-5 zeolite-supported Pt catalyst.
Figure 7. Dependence of Pt dispersion and hydroxyls density for HCHO conversion at 10 h on lactic acid treatment capacity of HZSM-5 zeolite-supported Pt catalyst.
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Figure 8. The proposed reaction pathway for HCHO oxidation over the Pt/HZ-8% LA catalyst.
Figure 8. The proposed reaction pathway for HCHO oxidation over the Pt/HZ-8% LA catalyst.
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Table 1. Texture characteristics, SiO2/Al2O3 mole ratio, Pt dispersion, and the ratio of Osur/Ototal for the catalysts.
Table 1. Texture characteristics, SiO2/Al2O3 mole ratio, Pt dispersion, and the ratio of Osur/Ototal for the catalysts.
SampleSBET (m2/g) [a]Dp (nm) [b]Vp (cm3/g) [c]SiO2/Al2O3 (%) [d]Pt Dispersion (%)Osur/Ototal (%)
HZ3960.60.1720.2--
Pt/HZ3960.60.1720.112.346.5
Pt/HZ-3% LA3750.60.1620.413.250.7
Pt/HZ-8% LA3710.60.1620.435.659.9
Pt/HZ-15% LA3740.60.1720.721.746.4
Pt/HZ-20% LA3750.60.1720.76.8-
[a] Specific surface area; [b] Average pore diameter; [c] Total pore volume; [d] The molar ratio of SiO2 to Al2O3.
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MDPI and ACS Style

Zhang, T.; Wang, S.; Li, X.; Du, Y.; Hu, J.; Jiang, S.; Guo, Y. Room-Temperature Complete Oxidation of Formaldehyde over Lactic Acid-Modified HZSM-5-Supported Pt Catalyst. Processes 2025, 13, 1440. https://doi.org/10.3390/pr13051440

AMA Style

Zhang T, Wang S, Li X, Du Y, Hu J, Jiang S, Guo Y. Room-Temperature Complete Oxidation of Formaldehyde over Lactic Acid-Modified HZSM-5-Supported Pt Catalyst. Processes. 2025; 13(5):1440. https://doi.org/10.3390/pr13051440

Chicago/Turabian Style

Zhang, Tongtong, Sijia Wang, Xingyuan Li, Yupeng Du, Jiajun Hu, Shi Jiang, and Yu Guo. 2025. "Room-Temperature Complete Oxidation of Formaldehyde over Lactic Acid-Modified HZSM-5-Supported Pt Catalyst" Processes 13, no. 5: 1440. https://doi.org/10.3390/pr13051440

APA Style

Zhang, T., Wang, S., Li, X., Du, Y., Hu, J., Jiang, S., & Guo, Y. (2025). Room-Temperature Complete Oxidation of Formaldehyde over Lactic Acid-Modified HZSM-5-Supported Pt Catalyst. Processes, 13(5), 1440. https://doi.org/10.3390/pr13051440

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