Preparation of CuO-Bi₂O₃-MgO/SiO₂ Spherical Catalyst and Its Formaldehyde Acetylenation Performance

Abstract

A spherical CuO-Bi₂O₃-MgO/SiO₂ catalyst was prepared using the coprecipitation-gel method. The study investigated the influence of the MgO/SiO₂ ratio on the catalyst structure and the activity of the catalyst in the preparation of 1,4-butanediol from formaldehyde acetylenation. The activity and filtration performance of the catalyst were compared with commercial samples. The study found that different MgO/SiO₂ ratios not only changed the size of CuO particles, the orientation of crystal faces, the specific surface area, and the pore distribution in the catalyst, but also adjusted the interaction between CuO and SiO₂. In addition, different MgO/SiO₂ ratios could significantly alter the structure of the catalyst and enhance its activity, with the highest activity achieved when the MgO/SiO₂ ratio was 1:3. Experimental results showed that the spherical CuO-Bi₂O₃-MgO/SiO₂ catalyst in this study achieved a selectivity of 96.3% and a conversion rate of 94.0% when reacting with formaldehyde at a concentration of 38 wt% for 12 h. The catalyst outperformed commercial samples in terms of activity and had the same strength level and better filtration separation performance as commercial samples.

1. Introduction

1,4-Butanediol is widely used in medicine, fiber, plastics, electroplating, and other fields. In recent years, with the increasing demand for environmental protection, 1,4-butanediol, as one of the raw materials for degradable plastics PBS (polybutylene succinate) and PBAT (polybutylene adipate/terephthalate) [1], has attracted more and more attention. The Reppe method of 1,4-butanediol is one of the important processes for the preparation of 1,4-butanediol.

HC≡CH + 2HCHO→HOCH2C≡CCH2OH

It uses the reaction of acetylene and formaldehyde to obtain 1,4-butynediol, and finally 1,4-butynediol is hydrogenated to obtain 1,4-butanediol [2,3,4]. As an intermediate product of 1,4-butanediol, the production process of 1,4-butynediol has a critical impact on the final product. A copper-based catalyst and slurry reactor are used for the reaction. The slurry bed reactor has specific requirements for catalyst activity, strength, and filtration performance. To meet the diverse application requirements of slurry bed reactors, modifying the catalyst support has emerged as a research hotspot in recent years. The research on catalyst support modification initially focused on CuO/Al₂O₃ and CuO/SiO₂. Currently, studies on CuO-Bi₂O₃/MgO-Al₂O₃-SiO₂ [5], CuO-Bi₂O₃/zeolite [6], CuO-Bi₂O₃@meso-SiO₂ [7], CuO-Bi₂O₃/Fe₃O₄-SiO₂-MgO [8], and CuO-Bi₂O₃/MgAl₂O₄ [9] have been reported. The research of Wang et al. [10] showed that the large number of acidic sites in Al₂O₃ can cause acetylene to polymerize on the catalyst surface, covering the active sites and reducing the activity of the catalyst. The introduction of magnesium species provides strong alkaline sites that play a crucial role in ≡C-H activation, due to their deprotonation ability, which exhibits a strong synergistic effect with Cu⁺ species, resulting in a significant increase in formaldehyde acetylene activity [11]. The CuO-Bi₂O₃/MgAl₂O₄ prepared by Guan et al. [9] improves the adverse effect of Al₂O₃ on the catalyst activity by using the alkalinity of MgO and the spinel structure of MgAl₂O₄. But the introduction of MgO reduces the specific surface area and pore volume of the catalyst, resulting in a limited improvement in the dispersion of CuO. SiO₂ boasts a favorable pore structure and a large specific surface area, which enable it to effectively disperse CuO species and maintain structural stability in the hydrothermal alkynylation reaction system. Meanwhile, the appropriate Brønsted acidity of SiO₂ facilitates the electrophilic addition of the C≡C bond in acetylene [12]. Zheng et al. [13] prepared Cu/Bi/SiO₂-MgO catalysts based on SiO₂-MgO supports and discovered that the Cu species in the catalysts exhibited small size and good dispersion, enabling them to efficiently catalyze the formaldehyde acetylenation reaction. Therefore, introducing MgO and SiO₂ into the Cu-Bi catalyst system can leverage the strengths of both components, thereby further enhancing the performance of the Cu-Bi catalyst.

When Si and Mg are introduced simultaneously into the catalyst, MgO-SiO₂ is typically prepared as the support first. There are generally three preparation methods for it. One method involves the preparation of soluble Mg salts loaded onto prepared SiO₂ [14]. Mg is primarily dispersed on the SiO₂ surface in the form of MgO, limiting further loading and dispersion of CuO species. Secondly, the prepared Mg(OH)₂ and silica sol are prepared through a mechanical wet-kneading method [15,16,17,18], resulting in limited dispersion of Si and Mg phases. The third method employs coprecipitation or gelation for direct preparation [19]. Mg species can penetrate the SiO₂ network, forming a dispersed Si-O-Mg structure, thereby adjusting the acid–base properties of MgO-SiO₂ materials. However, this method complicates the preparation of the carrier. Additionally, studies [20,21] have reported that the introduction of metal ions can modify the surface acidity and alkalinity of MgO by integrating them into the MgO lattice, subsequently influencing catalyst activity.

The existing literature focuses on the improvement of activity, preparation methods, and reaction mechanisms of formaldehyde acetylene catalysts, but there are no reports on the strength and filtration performance of the catalysts. However, as a slurry bed catalyst, formaldehyde ethynylation catalyst needs to balance high activity and good filtration performance.

Therefore, in order to avoid the disadvantage that the MgO-SiO₂ carrier has difficulties uniformly loading a high content of Cu, and at the same time, it can also obtain a spherical catalyst with good morphology, high activity, and easy separation, this paper uses a coprecipitation gel method to prepare a CuO-Bi₂O₃-MgO/SiO₂ catalyst, coprecipitates Cu, Bi, and Mg to obtain a cleaned Cu Bi Mg coprecipitation filter cake, then adds nano silica sol to disperse evenly, and finally, dries and calcines it to obtain a spherical catalyst. At the same time, a systematic study is conducted on the influence of MgO/SiO₂ ratios on the structure and activity of the catalyst, CuO grain size, specific surface area, and pore distribution. Finally, the activity, strength, and filtration performance are compared with commercial samples.

2. Materials and Methods

2.1. Materials and Characterization

Copper nitrate, bismuth nitrate, magnesium nitrate, silica sol, nitric acid, sodium carbonate, a formaldehyde solution, sodium acetate, 1,4-butynediol, and 1,4-butanediol are all commercially available AR-grade drugs.

The catalysts were analyzed by the following methods: N₂ adsorption–desorption analysis (ASAP 2460, Micromeritics, Norcross, GA, USA), X-ray powder diffraction (XRD, SmartLab SE, Rigaku, Rigaku Co., Ltd., Tokyo, Japan), X-ray photoelectron spectroscopy (XPS, Scientific K-Alpha, Thermo, Waltham, MA, USA), and scanning electron microscopy/transmission electron microscopy (SEM: MIRA LMS, TESCAN, Brno, Czech Republic, STEM: Talos F200X, Thermo Fisher, Waltham, MA, USA) containing STEM-EDS.

The specific surface area of the catalysts was calculated using the Brunauer–Emmett–Teller (BET) method, and the pore volume was calculated using the Barrett–Joyner–Halenda (BJH) model. The crystal structure of the catalysts was characterized by XRD (40 kV, 40 mA, Cu K radiation of = 1.54 Å) at room temperature with a scan speed of 10°/min and 2°/min, and a 2θ angle range of 10–80°. The chemical environment of the element of the catalysts were characterized by XPS (the excitation source was Al K α ray hv = 1486.6 eV, and the sample analysis area was 700 μm × 300 μm). In order to observe the morphological characteristics and element distribution of the catalyst, the catalyst was analyzed by SEM and TEM. Part of the sample was dispersed into ethanol solution for ultrasound, and then a few drops of the dispersed liquid were added to the molybdenum net, after drying and testing.

2.2. Catalysts Preparation

The catalysts with different MgO/SiO₂ ratios were prepared by the coprecipitation-gel method, and the mass percentages (weight%) of CuO/Bi₂O₃/MgO/SiO₂ were controlled to be 36:4:0:60, 36:4:10:50, 36:4:15:45, 36:4:20:40, 36:4:25:35, and 36:4:30:30 (the contents of CuO and Bi₂O₃ were constant at 36% and 4%). We added 150 mL of water to a 500 mL beaker and then added copper nitrate to dissolve it. Subsequently, we added bismuth nitrate to a 50 mL beaker, 2.0 mL of concentrated nitric acid, then 10 mL of water to dissolve it before adding the aforementioned copper nitrate solution. We weighed different amounts of magnesium nitrate and added it to the dissolved copper–bismuth solution. Then, we added 200 mL of water to a 1000 mL flask, stirred and heated to 80 °C, added a copper–bismuth–magnesium solution and a 10 wt% sodium carbonate solution to the flask in parallel flow, controlled the pH of the coprecipitation reaction to be 8 ± 0.3 and the reaction time to be 40 min, then we let it stand overnight, washed, and filtered. Then, we added a corresponding mass of silica sol to the filter cake with different MgO contents obtained by the above preparation method, stirred, added water to adjust the solid content to 20%, stirred and dispersed thoroughly for 30 min, sprayed dry, and then calcined the mixture to obtain CuO-Bi₂O₃/MgO-SiO₂ catalyst samples with different MgO contents, which were denoted as CB0MS, CB10MS, CB15MS, CB20MS, CB25MS, and CB30MS. Samples without silica sol were denoted as CBM, such as samples with a mass percentage of 36:4:15:0 for CuO/Bi₂O₃/MgO/SiO₂, denoted as CB15M, and samples with a mass percentage of 36:4:20:0, denoted as CB20M (Figure 1).

2.3. Catalysts Evaluation

The reaction was carried out in a 1000 mL jacketed reactor. First, 300 g of formaldehyde solution (20 wt%) and 25 g of catalyst were added to the reactor, which was then was sealed. The acetylene gas (150 mL/min) purified by lye and activated carbon was introduced into the reactor. When the temperature reached 90 °C, the acetylene flow rate was adjusted to 280 mL/min. The pH of the reaction system was monitored and adjusted to 5.0~5.5 with a sodium acetate solution. The activation of the catalyst and the ethynylation was carried out simultaneously. After 6 h of reaction, the solid–liquid mixture in the reactor was taken out and separated by filtration, and then the collected catalyst could be used for the next reaction.

Sodium thiosulfite titration was used to determine the content of formaldehyde before and after the reaction. The content of 1,4-butynediol in the reaction products was determined using gas chromatography. The gas chromatography model used was SP-6890, with an SE-54 chromatographic column and an FID detector. The column oven temperature was set at 130 °C, the detection oven temperature at 270 °C, and the vaporization oven temperature also at 270 °C. The formaldehyde present in the product and the raw material were determined using titration. The catalyst strength was determined by the change in catalyst particle size before and after the reaction. The catalyst particle size was measured using a laser particle size analyzer (LS-POP (6),OMEC, Zhuhai, China).

3. Results and Discussion

3.1. X-Ray Diffraction Characterization of Catalyst

As shown in Figure 2, after calcination, catalysts with varying MgO/SiO₂ ratios exhibited the characteristic diffraction peaks of CuO (JCPDS 48-1548). When the MgO/SiO₂ ratio exceeded 1:2, distinct MgO characteristic diffraction peaks (JCPDS 01-1235) appeared at 42.9° and 62.3°. At MgO/SiO₂ ratios of 1:3 and 1:2, the CuO diffraction peak widened, indicating changes in crystal growth orientation. The characteristic peak of the CuO (11-1) crystal plane (35.5°) was stronger than that of the (111) crystal plane (38.7°). Within a certain concentration range, MgO could influence the growth (orientation and size) of CuO grains. SiO₂ existed in an amorphous form. The absence of diffraction peaks for Bi₂O₃ in the figure suggests that the Bi₂O₃ crystal size was small and evenly dispersed within the catalyst. Using the half-peak width of the CuO (11-1) crystal plane, the crystal grain sizes of CuO catalysts with varying MgO/SiO₂ ratios were calculated according to the Scherrer formula, yielding values of 11.8 nm, 7.7 nm, 6.4 nm, 11.9 nm, and 14.4 nm, respectively.

To further analyze the factors affecting the CuO grain size and growth orientation in CB15MS and CB20MS catalysts with smaller grain sizes, we conducted an XRD analysis and a comparison between CB15M and CB20M catalysts without silicon and CB15MS and CB20MS catalysts with silicon added, as shown in Figure 3. The corresponding CuO grain sizes calculated according to the Scherrer formula are listed in

Table 1. Effect of silica sol on CuO grain size in catalyst.

Catalyst	CuO Grain Size, nm
CB15M	8.4
CB15MS	7.7
CB20M	8.0
CB20MS	6.4

. The Scherrer formula is as follows:

D = kλ/βcosθ

where D represents the grain diameter along the direction perpendicular to the crystal plane (nm), k is the Scherrer constant (usually 0.89), λ is the wavelength of the incident X-ray (Cu K 0.154056 nm), θ is the Bragg diffraction angle, and β is the half-width at half-maximum (rad) of the diffraction peak.

As shown in Figure 3, for both CB15M and CB20M samples without silicon, the diffraction peak intensity of the (11-1) crystal plane was stronger than that of the (111) crystal plane for CuO. Upon adding silica sol to the catalyst, the CuO diffraction peak broadened to some extent, and the grain size decreased slightly. Simultaneously, an amorphous SiO₂ peak was observed, suggesting that when Cu, Bi, and Mg were coprecipitated and subsequently mixed with silica sol, the dispersion of SiO₂ in the catalyst was limited, yet it still managed to reduce the grain size of the catalyst sample CuO. Referring to the CuO grain data in Table 1, an increase in MgO content also led to a reduction in CuO grain size. Consequently, the CuO grain size may be influenced by the synergistic effect of MgO and SiO₂.

3.2. N₂ Physical Adsorption Characterization of Catalyst

Figure 4a displays the N₂ adsorption–desorption isotherms for catalysts with varying MgO/SiO₂ ratios. The adsorption capacity of all samples gradually increased with the rise in relative pressure P/P₀. Within the range of 0.7 to 1.0 for the relative pressure P/P₀, the adsorption capacity surged, accompanied by a notable hysteresis loop. Based on the IUPAC classification, this behavior qualifies as a typical type IV isotherm, indicating that all catalysts exhibited the textural characteristics of mesoporous materials. Referring to Figure 4b, which illustrates the pore size distribution curves for each sample, it becomes evident that CB30MS exhibited a bimodal pore size distribution. A minor portion of pores was found at 2.5 nm, while the majority of pores were distributed at 15 nm.

The specific surface area, pore volume, pore diameter, and CuO grain size of each catalyst with different MgO/SiO₂ ratios are listed in

Table 2. Physical structure of catalysts with different MgO/SiO₂ ratios.

Samples	MgO/SiO2 Ratio	Specific Surface Area a	Pore Volume c	dpore a	dCuO b
		m2·g−1	cm3·g−1	nm	nm
CB10MS	1:5	60	0.318	21.26	11.8
CB15MS	1:3	96	0.518	21.65	7.7
CB20MS	1:2	83	0.312	14.99	6.4
CB25MS	1:1.4	80	0.369	18.45	11.9
CB30MS	1:1	62	0.293	18.97	14.4

^a Specific Surface Area and d_pore were calculated by the BET method; ^b d_CuO was calculated from the reflections of CuO (11-1) plane in the XRD using the Scherrer equation; ^c the pore volume was calculated by the BJH method.

. As shown in Table 2, the specific surface area of the catalyst initially increased and then decreased with the increase in Mg doping amount, with the MgO/SiO₂ ratio reaching its highest at 1:3. At a MgO/SiO₂ ratio of 1:3 and 1:2, the CuO grain size was smaller, measuring 7.7 nm and 6.4 nm, respectively. A smaller grain size is beneficial for enhancing the reactivity of the reaction.

3.3. XPS Characterization of Catalyst

As shown in Figure 5, all catalysts exhibited distinct Cu2p_3/2 and Cu2p_1/2 characteristic peaks around 935 eV and 955 eV, with satellite peaks corresponding to these peaks around 944 eV and 964 eV. The binding energy difference between the Cu2p_3/2 and Cu2p_1/2 characteristic peaks in all catalysts was approximately 20.0 eV, and the difference between the satellite peaks was also approximately 20.0 eV. These results indicate that Cu in the catalyst mainly exists in the form of Cu²⁺ [22]. However, when specific to catalysts with different MgO/SiO₂ ratios, the binding energies of their characteristic peaks were slightly different, indicating that the chemical environment of the Cu²⁺ present in the catalyst was different. To analyze the interaction between the main elements, we present the XPS spectra of Cu2p, Mg1s, Si2p, and O1s in Figure 6. As shown in Figure 6, the binding energies (BE) of the four main elements in the catalyst sample showed a similar trend with the increase in the MgO/SiO₂ ratio, indicating that the MgO/SiO₂ ratio had a significant impact on the presence of each element in the catalyst. The 1:3 MgO/SiO₂ ratio CB15MS sample is the turning point for the change. When the MgO/SiO₂ ratio increased to 1:3, the BE of Si began to decrease significantly, while the BE of Mg increased. The BE of Cu increased by 0.1 eV and then decreased by 0.2~0.4 eV, and the BE of O decreased slightly. When the MgO/SiO₂ ratio reached 1:1, the BE of the four main elements all increased significantly, but the BE of Si and O was still less than that of the 1:5 MgO/SiO₂ ratio, while the BE of Cu and Mg were significantly greater than that of the 1:5 MgO/SiO₂ ratio. These results indicate that the increase in MgO/SiO₂ ratio is achieved by altering its interaction with Si–O and Cu–O bonds, thereby changing the environment in which CuO exists.

3.4. SEM Characterization of Catalyst

Figure 7(a1,a2) illustrates the catalyst CB15M, prepared via Cu/Bi/Mg coprecipitation. Evidently, the catalyst surface predominantly featured agglomerated nano-particles, presenting a relatively porous and loose texture, abundant in visible pores. Upon heat treatment and molding, the surface transformed into a rough and irregular morphology, retaining a loose agglomeration of both large and small particles. Conversely, Figure 7(b1,b2) exhibits the heat-treated catalyst CB15MS, after the incorporation of SiO₂. Notably, the catalyst surface then comprised relatively regular agglomerations of nano-sized spherical particles, exhibiting a denser and more structured appearance, accompanied by visible large pores. Following heat treatment, the catalyst’s surface became notably more compact compared to its silicon-free counterpart, devoid of roughness or adhering small particles. Additionally, the particle size distribution became more uniform, evidently enhancing the catalyst’s wear resistance and filtration separation efficiency during usage.

3.5. HR-TEM Characterization of Catalyst

The catalyst CB15MS underwent characterization using high-angle annular dark field scanning (HAADF-TEM) and HR-TEM, with the results presented in Figure 8. As illustrated in Figure 8a, there are two bright spots on the left and right of the image, with a dark spot in the middle and a bright spot at the bottom. This suggests the presence of different elements or different structural substances. By further zooming in on the “V” shaped region in Figure 8a, we obtain Figure 8b. Upon zooming in on the boundary between the light and dark colors, it becomes evident that the light-colored region lacks lattice stripes and is in an amorphous phase, whereas the dark-colored region exhibits obvious lattice texture. In conjunction with the XRD characterization of the catalyst, we can infer that the light-colored “V” region is primarily composed of SiO₂, while the dark-colored region predominantly consists of crystalline nano-CuO. Figure 8c presents the lattice texture analysis of the dark areas. Clear lattice fringes are visible in different regions, with measured lattice spacings of 2.31 Å and 2.53 Å. Upon comparison with the XRD diffraction data of CuO (JCDPS 48-1548), they were identified as the (111) and (11-1) crystal planes of CuO, with corresponding abundance (I) values of 99% and 100%, respectively.

To further verify the elements and their distribution in various regions depicted in Figure 8a, high-angle annular dark field scanning and elemental energy dispersive spectroscopy (HAADF-TEM-EDS) were conducted. The obtained images are presented in Figure 9.

As illustrated in Figure 9a–c, SiO₂ was not only uniformly distributed in small amounts on the catalyst surface but also predominantly connected CuO-containing catalyst particles (refer to the light blue areas in the upper and lower parts of the figure). This connection led to the aggregation of CuBiMg composite particles into larger ones. Considering the aforementioned SEM images, this aggregation may explain the more rounded morphology of the catalyst and the denser “bonding” of surface particles. This further verifies that the dark areas within the amorphous lattice stripes depicted in Figure 9 correspond to amorphous SiO₂. Figure 9b,d demonstrate that Cu exhibited excellent dispersion on the catalyst.

3.6. The Influence of Different Mg/SiO₂ Ratios on the Activity and Structure of Catalysts

The data obtained from evaluating catalysts with varying MgO/SiO₂ ratios are presented in Figure 10. Evidently, as the MgO/SiO₂ ratio increased, the conversion rate, selectivity, and yield of the catalyst initially rose and then declined; the activity peaked when the ratio was 1:3. The previously mentioned XRD characterization revealed that doping with a certain amount of Mg could disperse the active component CuO and influence the growth orientation of crystal planes. Moreover, different MgO/SiO₂ ratios significantly affected the prepared specific surface area, pore volume, and pore size. Specifically, when the MgO/SiO₂ ratio was 1:3, the catalyst exhibited an optimal specific surface area and pore volume, coupled with a smaller CuO grain size.

To further investigate the effects of varying MgO/SiO₂ ratios on catalyst activity and structure, catalysts with differing ratios were reacted for 6 h under identical activity testing conditions and subsequently sampled for XRD characterization. The obtained spectrum is presented in Figure 11.

As illustrated in the figure, after 6 h of formaldehyde acetylenation reaction, only the characteristic peak of CuO (JCPDS 48-1548) and its corresponding crystal planes of the CB10MS catalyst remained visible, with only a slight decrease in peak intensity compared to the XRD pattern before the reaction (Figure 2). However, as the MgO/SiO₂ ratio increased, only the characteristic peaks corresponding to the (11-1) and (111) crystal planes of each sample were visible, and their intensities decreased compared to before the reaction.

Comparing the catalysts with different MgO/SiO₂ ratios before and after the reaction (as shown in Figure 2 and Figure 11), it is evident that before the reaction, CB15MS and CB20MS exhibited a stronger peak intensity corresponding to the (11-1) crystal plane than that corresponding to the (111) crystal plane. Conversely, CB25MS and CB30MS showed a stronger peak intensity corresponding to the (111) crystal plane than that corresponding to the (11-1) crystal plane. However, after the reaction, this situation reversed, with the weaker peak becoming stronger. This indicates that during the alkynylation reaction where HCOH reduced CuO on the CBMS catalyst, the electrons initially targeted Cu²⁺ on the crystal plane with a higher peak intensity or attacked Cu²⁺ on the crystal plane with a higher peak intensity at a faster rate than on the crystal plane with a weaker peak intensity, regardless of the crystal plane involved.

After conducting the formaldehyde acetylenation activity test on CB15MS for 6 h, the catalyst was recovered and reused in repeated reactions for six cycles. The activity of the catalyst is illustrated in Figure 12. As depicted in Figure 12, the initial reaction conversion rate and selectivity of the catalyst initially increased. After 18 h (after three cycles), the catalyst’s activity stabilized, indicating its good performance and no evident deactivation. Initially, the catalyst exhibited good adsorption properties, making formaldehyde easily adsorbed, thus resulting in a high conversion rate. However, the activity of Cu²⁺ reducing to Cu⁺ and generating copper acetylide and its hydrate was insufficient, leading to low selectivity. As time progressed, more active substances were produced, gradually leading the catalyst to enter a stable formaldehyde acetylenation reaction phase.

3.7. CBMS Catalyst Activity and Filtration Performance

Based on the patterns identified in the aforementioned research, under operating conditions close to those of industrial devices (38 wt% formaldehyde, 12 h reaction), a comparison was made between CBMS and commercial samples. The activity in formaldehyde acetylenation was evaluated and compared to that of industrial samples. The results are presented in

Table 3. Activity of the CBMS catalyst and commercial samples.

Sample	Conv.%	Sel.%	Yel.%
CBMS	94.0	96.3	90.5
Sample1	90.5	95.6	86.5
Sample 2	92.9	95.6	88.8

The reaction data were obtained under the condition of a formaldehyde concentration of 38 wt% and reaction time of 12 h.

. As shown in Table 3, the formaldehyde conversion rate, selectivity, and yield of the CBMS catalyst were 94.0%, 96.3%, and 90.5%, respectively, all of which higher than those of commercial samples 1 and 2. This indicates that the CBMS catalyst exhibits good catalytic activity for the acetylenation of formaldehyde.

Table 4. Particle size distribution of the CBMS catalyst and commercial samples.

Sample	Particle Size Distribution (D50, μm)
	Before Reaction	After Reaction	Change Value
CBMS	13.8	12.0	1.8
Sample 1	11.3	10.6	0.7
Sample 2	14.0	10.5	3.5

compares the particle sizes of CBMS and commercial samples before and after the reaction. It reveals that CBMS had a particle size of 13.8 μm, closely matching the 14.0 μm of commercial sample 2. The change in particle size of CBMS before and after the reaction was 1.8 μm, which fell between the 3.5 μm of commercial sample 1 and the 0.7 μm of commercial sample 2, indicating that CBMS possessed moderate mechanical strength. Due to its larger initial size and moderate strength, CBMS maintained a higher particle size after the reaction compared to the two commercial samples.

To investigate the filtration performance of the catalysts, a comparison of filtration times was conducted between the catalyst before and after the reaction, with the results presented in Figure 13. As observed from the figure, regardless of the filtration times before and after the reaction, CBMS required the least amount of time, whereas the filtration of industrial sample 2 took the longest. This experiment demonstrated that the filtration performance of CBMS surpassed that of the two industrial samples.

4. Conclusions

In this study, a CuO-Bi₂O₃-MgO/SiO₂ catalyst with a spherical shape for formaldehyde acetylenation was prepared. The study found that different MgO/SiO₂ ratios could affect the surface properties, texture, interaction between CuO and the carrier silicon–magnesium, as well as the dispersion and distribution of surface CuO on the catalyst surface. Experiments showed that the catalyst with a MgO/SiO₂ ratio of 1:3 exhibited the highest specific surface area (96 m²/g), smaller CuO crystal size (7.7 nm), and unique crystal orientation (11-1), resulting in the highest activity for the formaldehyde ethynylation reaction. After being recycled and used six times, the catalyst still maintained stable performance and showed no tendency to deactivate. The CuO-Bi₂O₃-MgO/SiO₂ catalyst not only maintained the same strength level as commercial samples but also demonstrated excellent activity (conversion rate of 94.0%, selectivity of 96.3%) and filtration performance, indicating its broad commercial prospects.

5. Patents

Ping Luo, Gang Guan, Feng-Yun Ma, Xiang-Yu Wang, Hao Tao, Xiao-Lin Zhang, Xiao-Ding Li. 2024. A Cu-Bi-Mg/SiO₂ catalyst, its preparation method, and its application. CN202211000659.8, 24 November.