Au-based catalyst for preparing dihydroxyacetone through selective oxidation of glycerol and preparation method of Au-based catalyst

Abstract

The invention provides an Au-based catalyst for preparing dihydroxyacetone by selective oxidation of glycerol and a preparation method thereof. The general formula of the catalyst is Au / M1M2AlOx, M1 is one or more of Mg, Zn, Co or Cu, M2 is one of Ce, Ga or Fe, the loading capacity of precious metal Au is 0.1-10 wt%, and the average particle size is 2-50 nm. The carrier M1M2AlOx is a composite metal oxide formed by thermally induced topology of M1M2Al-LDHs, and has abundant oxygen vacancies and alkaline sites. The catalyst is obtained by firstly synthesizing M1M2Al-LDHs, then loading noble metal Au and carrying out atmosphere induction roasting. The strong interaction between the metal and the carrier is beneficial to the formation of Au < 3 + > species, further oxidation of an intermediate product can be inhibited, and the selectivity of the catalyst can be improved. The DHA is prepared by efficiently catalyzing glycerol oxidation in a heterogeneous alkali medium, and the preparation method is simple and easy to operate. The reaction process is mild in condition and environment-friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysis, and in particular relates to a method for preparing an Au-based catalyst and application thereof in the selective oxidation of biomass alcohol glycerol to prepare dihydroxyacetone. Background Art

[0002] In recent years, biomass resources have been considered one of the most promising new energy sources to replace traditional fossil fuels due to their abundant reserves, widespread distribution, renewable nature, low pollution, and carbon neutrality. Glycerol is a typical biomass-based platform compound and a major byproduct of the biodiesel and bioethanol industries. Its effective utilization is crucial for promoting the sustainable development of the biomass industry chain. Glycerol is a highly functional molecule with three hydroxyl groups. It can be produced into a variety of high-value-added chemicals through oxidation, hydrogenolysis, esterification, dehydration, and reforming to produce hydrogen. Among glycerol's many downstream products, 1,3-dihydroxyacetone (DHA) is one of the most economically valuable. It can be used as a food additive, preservative, antiviral agent, and cosmetic formulation ingredient, finding widespread application in the food, pharmaceutical, and cosmetics industries. Furthermore, DHA is chemically active and can participate in polymerization or condensation reactions to synthesize a variety of organic compounds. Therefore, the selective oxidation of glycerol to produce DHA has significant economic and academic value.

[0003] Currently, the industry mainly uses biofermentation to produce DHA. However, this method faces problems such as long cycle time, low yield of target product, and complex subsequent separation. In recent years, heterogeneous catalysis has attracted widespread attention in the field of selective catalytic oxidation of glycerol to prepare high-value-added downstream products due to its mild conditions, low environmental pollution, and easy separation of products and catalysts. In recent years, in the research progress of catalysts for the selective catalytic oxidation of glycerol, supported precious metal catalysts such as Au-based, Pt-based, and Pd-based have shown excellent performance. In the literature "Stable and active Au catalyst supported on CeMnO3Perovskite for Selective Oxidation of Glycerol, Inorganic Chemistry., 2023, 62, 21, 8145-8157", the authors found that supported Au-based catalysts have the advantages of good antioxidant and anti-poisoning capabilities, but they still face problems such as difficulty in activating secondary hydroxyl groups, difficulty in controlling the oxidation depth, and poor stability. In the literature Insights into the Multiple Synergies of Supports in theSelective Oxidation of Glycerol to Dihydroxyacetone:Layered Double HydroxideSupported Au,ACS Catal.,2020,10,12437-12453, the authors improved the conversion of glycerol by adjusting the density of basic sites on the catalyst surface, achieving a glycerol conversion rate of 73% and a DHA selectivity of 64%. In addition, in the literature The Effect of Oxygen Vacancies in ZnO at an Au / ZnOInterface on its Catalytic Selective Oxidation of Glycerol,J Catal,2019,377,271-282, the authors introduced oxygen vacancies in the support to enhance the interaction between the metal and the support, achieving a glycerol conversion rate of 75%. In the literature The preparation of AuPd / ZnO-CuO for directional oxidation of glycerol to DHA, Catal.Sci.Technol., 2020, 10, 6223-6234, the authors obtained a glycerol conversion rate of 75% and a DHA selectivity of 76% by enhancing the interaction between Au nanoparticles and the carrier.However, achieving multi-site synergistic matching remains challenging, and it is difficult to promote efficient activation of glycerol while achieving high selectivity. Therefore, it is extremely challenging to design a catalyst with both high activity and high selectivity.

[0004] Since the glycerol oxidation reaction requires multi-site synergistic matching, it is necessary to controllably construct surface alkaline sites and oxygen vacancies to synergistically promote glycerol conversion, while strengthening the interaction between the metal and the support to improve DHA selectivity. The present invention is based on a layered composite metal hydroxide (LDHs) material platform, and based on the elemental tunability and topological transformation characteristics of LDHs, a series of Au-based catalysts with different elemental compositions are prepared. Specifically, the Au-based catalyst achieved a glycerol conversion rate of 57.2% to 86.1% and a DHA selectivity of 46.8% to 80.5% in the selective oxidation of glycerol. This work provides a systematic understanding of the synergistic effect and reaction mechanism of the catalyst active sites, and provides an effective design idea for the rational design and preparation of efficient heterogeneous catalysts for biomass resource conversion, which has important economic and academic significance for promoting the sustainable development of biomass energy and chemicals. Summary of the Invention

[0005] The present invention aims to provide a catalyst for the selective oxidation reaction of glycerol and a preparation method thereof. The catalyst has outstanding catalytic performance.

[0006] The chemical formula of the Au-based catalyst provided by the present invention is Au / M1M2AlO x , wherein M1 is one or more of Mg, Zn, Co or Cu; M2 is one of Ce, Ga or Fe; M1M2AlO x (x=3-6) is a carrier, which is a composite metal oxide formed by M1M2Al-LDHs topology; the loading amount of the noble metal Au is 0.1-10 wt%, and the average particle size of Au is 2-50 nm.

[0007] The specific preparation steps of the above catalyst are as follows:

[0008] A. Soluble M1 2+ 、M2 3+ Salt and aluminum salt precursors are dissolved in deionized water to prepare a mixed salt solution, wherein M1 2+ Mg 2+ 、Zn 2+ 、Co 2+ 、Cu 2+ One or more of; M2 3+ Ce 3+ 、Ga 3+ 、Fe 3+ One of the 2+ :M 3+The molar ratio of M is 2 to 4; 2+ and M 3+ The total ion concentration is 0.1 to 0.9 mol / L; the alkali is dissolved in deionized water to prepare an alkali solution with a concentration of 0.5 to 2 mol / L, wherein the alkali solution is a mixed solution of NaOH or KOH and Na2CO3 or NaHCO3;

[0009] B. The mixed salt solution and alkaline solution prepared in step A were added dropwise to a three-necked flask at a rate of 1-3 mL / min, maintaining the pH of the solution at 9-11 during the titration process; after completion of the operation, the resulting suspension was crystallized at 60-80°C for 6-24 hours; washed and centrifuged until the supernatant was neutral, and dried to obtain the M1M2Al-LDHs precursor;

[0010] C. The LDHs support prepared in step B is uniformly dispersed in deionized water, and an alkali and Au metal salt are added, wherein the Au loading is 0.1-10 wt % and the amount of the alkali is 400-1000 times the amount of Au. The resulting suspension is stirred at 50-90°C for 3-8 hours, and after cooling to room temperature, NaBH4 is added for liquid-phase reduction. The supernatant is washed until neutral and dried to obtain an Au-loaded LDHs catalyst, denoted as Au / M1M2Al-LDHs. The alkali is one of NaOH or urea; the Au metal salt is one of HAuCl4 and KAuCl4.

[0011] D. The Au / M1M2Al-LDHs obtained in step C were heated to 200°C~800°C at a heating rate of 2~10°C / min in a mixed atmosphere of CO2, N2 or CO2 / N2 and maintained for 3~6h, and then cooled to room temperature to obtain Au / M1M2AlO x .

[0012] The Au / M1M2AlO x The catalyst is used in the preparation of dihydroxyacetone by oxidizing glycerol, and its characteristics include: a molar ratio of Au to glycerol of 1:10-500, a reaction temperature of 30-90°C, a reaction time of 1-24h, and a pressure of 0.1-0.6MPa.

[0013] The characteristics of the present invention are: the catalyst uses LDHs material as a precursor, utilizes its adjustable characteristics of layer elements, and selects suitable metal elements to synthesize M1M2Al-LDHs with suitable basic sites. Based on the structural topological effect of LDHs, oxygen vacancies are introduced during the topological transformation process of heat treatment, accelerating the breaking of chemical bonds around oxygen atoms and the escape of lattice oxygen in a high-temperature oxygen-deficient environment, thereby constructing rich oxygen vacancy species; at the same time, the bimetallic oxide formed by LDHs after structural topology exhibits stronger alkalinity. In addition, under the strong interaction between metal and support, it is beneficial for Au 3+The formation of species, whose existence can inhibit the further oxidation of intermediates, is beneficial to the improvement of dihydroxyacetone selectivity.

[0014] Figure 1 The X-ray photoelectron spectroscopy (XPS) diagram of the catalyst prepared in Example 2, a is the XPS spectrum of Au 4f, b is the XPS spectrum of O1s. It can be seen from Figure a that the catalyst contains Au 0 、Au + 、Au 3+ Species, including Au 3+ The content of species is 30.3%. As can be seen from Figure a, the catalyst contains O α , O β , O γ Species, including O β / O α The ratio is related to the oxygen vacancy content on the catalyst surface and is 1.6 (43.7 / 28.6).

[0015] Figure 2 This is the electron paramagnetic resonance (EPR) spectrum of Example 1. It can be seen from the figure that an obvious characteristic peak appears near g=2.003, indicating that the catalyst contains oxygen vacancies.

[0016] Figure 3 This is the CO2-temperature programmed desorption (CO2-TPD) curve of Example 4. It can be seen from the figure that the catalyst has a large desorption peak at 264°C, indicating that the catalyst contains medium basic sites.

[0017] Figure 4 This is the in-situ infrared spectrum of acetone desorption in Example 5. It can be seen from the figure that the peak intensity of the C=O characteristic peak in the spectrum decreases in the temperature range of 20-80°C, indicating that there is a relatively suitable interaction force between the catalyst and C=O.

[0018] Figure 5 The experimental results of the catalyst prepared in Example 3 in the glycerol oxidation reaction show that the dihydroxyacetone selectivity reaches 80.5% at 4 hours and the glycerol conversion rate reaches 95.9% at 6 hours.

[0019] Figure 6 The experimental results of the catalyst prepared in Example 5 in the glycerol oxidation reaction show that the dihydroxyacetone selectivity reaches 83.3% at a temperature of 60°C, and the glycerol conversion rate reaches 81.7% at 80°C.

[0020] Beneficial effects of the present invention:

[0021] 1. The characteristics of the present invention are that the basic sites and oxygen vacancies of Au-based catalysts with adjustable LDHs precursor elements and topological transition properties are constructed. Such catalysts can be used in the selective oxidation of glycerol with molecular oxygen as an oxidant to promote the improvement of glycerol conversion rate. In addition, in the case of Au 3+ Under the action of species and moderate alkaline sites, timely desorption of key intermediates is achieved, and efficient and directional conversion of target products is realized.

[0022] 2. The catalyst prepared by the present invention is used for the reaction process of glycerol oxidation to prepare dihydroxyacetone. The reaction conditions are mild, environmentally friendly, and the equipment corrosion is small. It is easy to recycle and reuse, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XPS spectrum of Example 2.

[0024] Figure 2 This is the EPR spectrum of Example 1.

[0025] Figure 3 This is the CO2-TPD curve of Example 4.

[0026] Figure 4 This is the in-situ infrared spectrum of acetone desorption in Example 5.

[0027] Figure 5 This is the experimental result of the catalyst prepared in Example 3 in the glycerol oxidation reaction, and is a performance evaluation diagram of glycerol conversion and selectivity versus reaction time.

[0028] Figure 6 This is the experimental result of the catalyst prepared in Example 5 in the glycerol oxidation reaction, and the performance evaluation diagram of glycerol conversion rate and selectivity versus reaction temperature. DETAILED DESCRIPTION

[0029] Example 1

[0030] A. Prepare the CuMgFeAl-LDHs support using a coprecipitation method. Dissolve 0.02 mol Cu(NO3)2, 0.02 mol Mg(NO3)2, 0.01 mol Fe(NO3)3, and 0.01 mol Al(NO3)3 metal precursor salts in 100 mL of deionized water to obtain a mixed salt solution A. Dissolve 0.015 mol NaOH and 0.03 mol Na2CO3 in 100 mL of deionized water to obtain a mixed alkaline solution B. Solution A was added dropwise at a rate of 3.0 mL / min to a three-necked flask containing 100 mL of deionized water. At the same time, the addition rate of solution B was controlled to keep the pH of the system at 9.5±0.5. The solution was maintained at 70°C for 20 h, centrifuged, washed, and the supernatant was washed until the pH was 7. The solution was further dried to obtain CuMgFeAl-LDHs.

[0031] B. Au metal salt loading using the precipitation deposition method: 1 g of CuMgFeAl-LDHs, 2.44 g of urea, and 2 mL of HAuCl4 (10 mg Au / mL) were uniformly dispersed in 50 mL of deionized water and stirred at 60°C for 8 h. After cooling to room temperature, 38.4 mg of NaBH4 (10 mol NaBH4 / mol Au) was added and stirred for 30 min. The mixture was centrifuged and washed until the supernatant had a pH of 7. The supernatant was then dried to obtain Au / CuMgFeAl-LDHs.

[0032] C. The Au / CuMgFeAl-LDHs obtained in step B were placed in a mixed atmosphere of 15% CO2 and 85% N2 and heated to 500°C at a rate of 2°C / min and kept warm for 5h. After cooling to room temperature, the Au / CuMgFeAlO x catalyst.

[0033] The catalyst prepared above was used in a glycerol oxidation experiment: 100 mg of the catalyst was placed in a microautoclave equipped with magnetic stirring, followed by 10 mL of a 10 mmol / L glycerol solution. The reaction temperature was maintained at 40°C and the oxygen pressure was maintained at 0.5 MPa. After 6 hours of reaction, the liquid product was collected and analyzed using a Shimadzu LC-20AT high-performance liquid chromatograph. The results are shown in Table 1.

[0034] Example 2

[0035] A. CoZnCeAl-LDHs support was prepared using a coprecipitation method. 0.02 mol Co(NO3)2, 0.02 mol Zn(NO3)2, 0.01 mol Ce(NO3)3, and 0.01 mol Al(NO3)3 metal precursor salts were dissolved in 100 mL of deionized water to obtain a mixed salt solution A. 0.015 mol NaOH and 0.03 mol Na2CO3 were dissolved in 100 mL of deionized water to obtain a mixed alkaline solution B. Solution A was added dropwise at a rate of 3.0 mL / min to a three-necked flask containing 100 mL of deionized water. The addition rate of solution B was simultaneously controlled to keep the pH of the system at 9.5±0.5. The solution was maintained at 70°C for 20 h, centrifuged, washed, and the supernatant was washed until its pH was 7. The solution was then dried to obtain CoZnCeAl-LDHs.

[0036] B. Loading Au metal salt using precipitation deposition method: 1 g of CoZnCeAl-LDHs, 0.61 g of urea, and 0.5 mL of HAuCl4 (10 mg Au / mL) were uniformly dispersed in 50 mL of deionized water and stirred at 70°C for 8 h. After cooling to room temperature, 9.6 mg of NaBH4 (10 mol NaBH4 / mol Au) was added and stirred for 30 min. The mixture was centrifuged and washed until the supernatant had a pH of 7. The supernatant was then dried to obtain Au / CoZnCeAl-LDHs.

[0037] C. The Au / CoZnCeAl-LDHs obtained in step B were placed in CO2 and heated to 500℃ at a heating rate of 5℃ / min and kept warm for 3h. After cooling to room temperature, the Au / CoZnCeAlO x catalyst.

[0038] The catalyst prepared above was used in a glycerol oxidation reaction experiment: the method and conditions were the same as in Example 1, and the results are shown in Table 1.

[0039] Example 3

[0040] A. Prepare the CuZnGaAl-LDHs support using a co-precipitation method. Dissolve 0.02 mol Cu(NO3)2, 0.02 mol Zn(NO3)2, 0.01 mol Ga(NO3)3 and 0.01 mol Al(NO3)3 metal precursor salts in 100 mL of deionized water to obtain a mixed salt solution A. Dissolve 0.015 mol NaOH and 0.03 mol Na2CO3 in 100 mL of deionized water to obtain a mixed alkali solution B. Solution A was added dropwise to a three-necked flask containing 100 mL of deionized water at a rate of 3.0 mL / min. At the same time, the addition rate of solution B was controlled to control the pH of the system at 9.5±0.5, and the mixture was maintained at 70°C for 20 h. After completion, the mixture was centrifuged and washed until the supernatant pH = 7, and further dried to obtain CuZnGaAl-LDHs.

[0041] B. Loading Au metal salt using precipitation deposition: 1 g of CuZnFeAl-LDHs, 1.22 g of urea, and 1 mL of HAuCl4 (10 mg Au / mL) were uniformly dispersed in 50 mL of deionized water and stirred at 80°C for 6 h. After cooling to room temperature, 19.2 mg of NaBH4 (10 mol NaBH4 / mol Au) was added and stirred for 30 min. The mixture was centrifuged and washed until the supernatant had a pH of 7. The supernatant was then dried to obtain Au / CuZnGaAl-LDHs.

[0042] C. The Au / CuZnGaAl-LDHs obtained in step B were placed in N2 and heated to 400℃ at a heating rate of 10℃ / min and kept warm for 3h. After cooling to room temperature, the Au / CuZnGaAlO x catalyst.

[0043] The catalyst prepared above was used in a glycerol oxidation reaction experiment: the method and conditions were the same as in Example 1, and the results are shown in Table 1.

[0044] Example 4

[0045] A. CoZnFeAl-LDHs support was prepared using a coprecipitation method. 0.02 mol Co(NO3)2, 0.02 mol Zn(NO3)2, 0.01 mol Fe(NO3)3 and 0.01 mol Al(NO3)3 metal precursor salts were dissolved in 100 mL of deionized water to obtain a mixed salt solution A. 0.015 mol NaOH and 0.03 mol Na2CO3 were dissolved in 100 mL of deionized water to obtain a mixed alkali solution B. Solution A was added dropwise to a three-necked flask containing 100 mL of deionized water at a rate of 3.0 mL / min. At the same time, the addition rate of solution B was controlled to keep the pH of the system at 9.5±0.5, and the mixture was maintained at 70°C for 20 h. After completion, the mixture was centrifuged and washed until the supernatant had a pH of 7, and further dried to obtain CoZnFeAl-LDHs.

[0046] B. Au metal salt loading using the precipitation deposition method. 1 g of CoZnFeAl-LDHs, 1.22 g of urea, and 1 mL of HAuCl4 (10 mg Au / mL) were uniformly dispersed in 50 mL of deionized water and stirred at 60°C for 8 h. After cooling to room temperature, 19.2 mg of NaBH4 (10 mol NaBH4 / mol Au) was added and stirred for 30 min. The mixture was centrifuged and washed until the supernatant had a pH of 7. The supernatant was then dried to obtain Au / CoZnFeAl-LDHs.

[0047] C. The Au / CoZnFeAl-LDHs obtained in step B were placed in CO2 and heated to 300℃ at a heating rate of 10℃ / min and kept warm for 3h. After cooling to room temperature, the Au / CoZnFeAlO x catalyst.

[0048] The catalyst prepared above was used in a glycerol oxidation reaction experiment: the method and conditions were the same as in Example 1, and the results are shown in Table 1.

[0049] Example 5

[0050] A. Prepare the CoMgFeAl-LDHs support using a coprecipitation method. Dissolve 0.02 mol Co(NO3)2, 0.02 mol Mg(NO3)2, 0.01 mol Fe(NO3)3, and 0.01 mol Al(NO3)3 metal precursor salts in 100 mL of deionized water to obtain a mixed salt solution A. Dissolve 0.015 mol NaOH and 0.03 mol Na2CO3 in 100 mL of deionized water to obtain a mixed alkali solution B. Solution A was added dropwise at a rate of 3.0 mL / min to a three-necked flask containing 100 mL of deionized water. At the same time, the addition rate of solution B was controlled to keep the pH of the system at 9.5±0.5. The solution was maintained at 70°C for 20 h. After completion, the solution was centrifuged and washed until the supernatant had a pH of 7, and then dried to obtain CoMgFeAl-LDHs.

[0051] B. Loading Au metal salt using precipitation deposition: 1 g of CoMgFeAl-LDHs, 2.44 g of urea, and 2 mL of HAuCl4 (10 mg Au / mL) were uniformly dispersed in 50 mL of deionized water. The mixture was stirred at 60°C for 8 h. After cooling to room temperature, 38.4 mg of NaBH4 (10 mol NaBH4 / mol Au) was added and stirred for 30 min. The mixture was centrifuged and washed until the supernatant had a pH of 7. The supernatant was then dried to obtain Au / CoMgFeAl-LDHs.

[0052] C. The Au / CoMgFeAl-LDHs obtained in step B were placed in CO2 and heated to 600℃ at a heating rate of 5℃ / min and kept warm for 3h. After cooling to room temperature, the Au / CoMgFeAlO x catalyst.

[0053] The catalyst prepared above was used in a glycerol oxidation reaction experiment: the method and conditions were the same as in Example 1, and the results are shown in Table 1.

[0054] Table 1

[0055]

[0056] As can be seen from Table 1, the catalytic performance of the catalyst of the present invention under alkali-free conditions is at the upper level of the literature. Specifically, Example 1 has a significant advantage in glycerol conversion, Example 2 has a significant advantage in DHA selectivity, and Examples 3, 4, and 5 maintain DHA selectivity above 75.4% when the glycerol conversion is greater than 76.3%, achieving a synergistic improvement in conversion and selectivity. In particular, the DHA yield in Example 3 reaches 69.3%.

Claims

1. A method for preparing an Au-based catalyst for selective oxidation of glycerol to dihydroxyacetone, characterized in that Here are the steps: A. Soluble M1 2+ and M2 3+ Salt and aluminum salt are dissolved in deionized water to prepare a mixed salt solution, wherein M1 2+ Mg 2+ 、Zn 2+ 、Co 2+ 、Cu 2+ One or two of M2 3+ Ce 3+ 、Ga 3+ 、Fe 3+ One of the 2+ :M 3+ The molar ratio of M is 2 to 4; 2+ and M 3+ The total ion concentration is 0.1 to 0.9 mol / L; a mixed alkali solution is prepared by dissolving an alkali in deionized water, wherein the alkali is a mixed solution of NaOH or KOH and Na2CO3 or NaHCO3; the concentration of the alkali solution is 0.5 to 2 mol / L; B. The mixed salt solution and alkaline solution prepared in step A are dripped into the reactor at a rate of 1-3 mL / min, and the pH of the solution is maintained at 9-11 during the titration process; after the operation is completed, the resulting suspension is crystallized at 60-80°C for 6-24 hours; washed and centrifuged until the supernatant is neutral, and dried to obtain the M1M2Al-LDHs precursor; C. The LDHs support prepared in step B is uniformly dispersed in deionized water, and an alkali and an Au metal salt are added, wherein the amount of the alkali is 400 to 1000 times the amount of the Au. The resulting suspension is stirred at 50 to 90° C. for 3 to 8 hours, and after cooling to room temperature, NaBH4 is added for liquid-phase reduction. The suspension is washed until the supernatant is neutral and dried to obtain an Au-loaded LDHs catalyst, denoted as Au / M1M2Al-LDHs. The alkali is one of NaOH and urea; and the Au metal salt is one of HAuCl4 and KAuCl4. D. The Au / M1M2Al-LDHs obtained in step C was heated to 200-800°C in an atmosphere at a heating rate of 2-10°C / min and maintained for 3-6 hours, and then cooled to room temperature to obtain Au / M1M2AlO x ; The atmosphere is pure CO2, pure N2 or a mixed atmosphere of 15% CO2 and 85% N2.

2. The method according to claim 1, characterized in that The molar ratio of NaOH or KOH to Na2CO3 or NaHCO3 is 1:1 to 1:

4.

3. The method according to claim 1, characterized in that The active metal Au loading amount is 0.1-10 wt%.

4. The method according to claim 1, wherein The particle size of the active metal Au supported on the catalyst carrier is less than 5.0 nm.

5. The catalyst prepared by the method according to any one of claims 1 to 4.

6. Use of the catalyst according to claim 5 in the selective oxidation of glycerol to produce dihydroxyacetone.

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