Sacrificial H2 production over Pt/TiO2 using alcohols (
Abstract
Biodiesel fuel (BDF) has gained much attention as a new sustainable energy alternative to petroleum-based fuels. BDF is produced by transesterification of vegetable oil or animal fats with methanol along with the co-production of glycerol. Indeed, transesterification of vegetable oil (136.5 g) with methanol (23.8 g) was performed under heating at 61°C for 2 h in the presence of NaOH (0.485 g) to produce methyl alkanoate (BDF) and glycerol in 83.7 and 73.3% yields, respectively. Although BDF was easily isolated by phase separation from the reaction mixture, glycerol and unreacted methanol remained as waste. In order to construct a clean BDF synthesis, the aqueous solution of glycerol and methanol was subjected to sacrificial H2 production over a Pt-loaded TiO2 catalyst under UV irradiation by high-pressure mercury lamp. H2 was produced in high yield. The combustion energy (ΔH) of the evolved H2 reached 100.7% of the total ΔH of glycerol and methanol. Thus, sacrificial agents such as glycerol and methanol with all of the carbon attached to oxygen atoms can continue to serve as an electron source until their sacrificial ability was exhausted. Sacrificial H2 production will provide a promising approach in the utilization of by-products derived from BDF synthesis.
Keywords
- BDF
- photocatalyst
- TiO2
- sacrificial agent
- glycerol
- hydrogen
1. Introduction
The major issue in the current world is an urgent need to stop the increase of CO2 levels. A large amount of consumption of fossil resources causes serious environmental problems such as global warming and air pollution. Therefore, biofuels such as bioethanol, bio-hydrogen, and biodiesel (BDF) have gained much attention as renewable and sustainable energy alternative to petroleum-based fuels [1]. However, the problems to be solved for practical uses still remain in each biofuel. In bioethanol, the ethanol concentrations are still too low to isolate pure ethanol by distillation at a low energy cost [2, 3]. Bio-hydrogen is isolated spontaneously from reaction mixtures without operations to separate. However, it is needed to construct newly a supply system to vehicles.
BDF is produced by transesterification of vegetable oil or animal fats with methanol along with the co-production of glycerol [Eq. (1)] [4]. Although methyl alkanoate (BDF) is easily isolated by phase separation, a mixture of glycerol and unreacted methanol remains in aqueous solution as waste. New utilization of these wastes is required. Reforming of glycerol has been extensively investigated through pyrolysis [5, 6], steam gasification [7, 8], and biological reforming [9, 10]. We have focused on photocatalytic reforming over titanium dioxide (TiO2) [11]:
TiO2 has a semiconductor structure with 3.2 eV of bandgap, which corresponds to 385 nm of light wavelength [12]. Therefore, the TiO2 can be excited by 366 nm emitted from a high-pressure mercury lamp. Irradiation of the TiO2 induces charge separation into electrons and holes (Figure 1). Electron excited to the conduction band serves to reduce water to H2. Evolution of H2 is usually accelerated by deposition of noble metals (Pt, Pd, and Au) onto the TiO2. The positive charge (hole) oxidizes hydroxide absorbed on the surface of TiO2 to generate hydroxyl radicals, which is eventually transformed to O2 [13]. However, spontaneous conversion of hydroxyl radical into O2 is inefficient. Moreover, water splitting into O2 and H2 is a large uphill reaction, resulting in rapid reverse reaction.
On the other hand, the hydroxyl radicals can be effectively consumed by the use of electron-donating sacrificial agents (hole scavengers), thus accelerating the H2 production (Figure 1) [14]. This method is named “sacrificial H2 production.” The sacrificial H2 production is an uphill process, but the energy change is small. Therefore, the sacrificial H2 production proceeds more smoothly compared with water splitting without sacrificial agents, thus providing a convenient method to generate H2 [15]. When one equivalent of hydroxyl radical is consumed, one equivalent of electron is generated to produce 0.5H2.
During our investigations on sacrificial H2 production over a Pt-loaded TiO2 (Pt/TiO2) [15], it was found that sacrificial agents with all of the carbon attached oxygen atoms such as saccharides, polyalcohols (e.g., arabitol, glycerol, 1,2-ethandiol), and methanol continued to serve as an electron source until their sacrificial ability was exhausted. Glycerol (
2. Outline of conversion of glycerol to hydrogen
Generally, biomass reforming is started by the production of water-soluble materials from biomass through biological treatment as well as chemical reaction [17, 18]. The resulting water-soluble materials (saccharides, amino acids) are converted to biofuels such as ethanol, methane, and hydrogen through various catalytic reactions in aqueous solution. Our biomass reforming is performed in aqueous solution through sacrificial H2 production over Pt/TiO2 using water-soluble materials derived from lignocelluloses [19, 20, 21] and chlorella [22] (Figure 2).
In this chapter, we will show H2 production through sacrificial H2 production over Pt/TiO2 using
3. Materials and method
3.1 Apparatus
NMR spectra were taken on a Bruker AV 400M spectrometer for CDCl3 solution. LC-MS analysis were performed on a Waters Alliance 2695 under conditions (ESI ionization, capillary voltage 3.5 kV, source temperature 120°C and desolvation temperature 350°C) using column (Waters, SunFire C18, 2.1 mmΦ × 150 mm) and 1% formic acid in MeOH-H2O (6:4) as an eluent solution. GLC analysis of solution was performed on a Shimadzu 14A gas liquid chromatograph with FID detector at a temperature raised from 50 to 250°C using a capillary column (J & W CP-Sil 5CB, 0.32 mmΦ × 50 m).
3.2 Photoreaction apparatus
Reaction vessel was a cylindrical flask with 30 cm of height and 7.5 cm of diameter, which had three necks on the top. A high-pressure mercury lamp (100 W, UVL-100HA, Riko, Japan), which emitted mainly a light at 313 and 366 nm, was inserted into the large central neck of the reaction vessel. The reaction vessel was connected to a measuring cylinder with a gas-impermeable rubber tube to collect the evolved gas. The reaction vessel was set in a water bath to keep it at 20°C. The stirring of the solution was performed by magnetic stirrer.
3.3 Preparation of photocatalyst
Almost all research has used TiO2 in anatase form such as P25 (Degussa Co. Ltd., Germany) and ST01 (Ishihara Sangyo Co. Ltd., Japan) for photocatalytic H2 production. A Pt-loaded TiO2 catalyst (Pt/TiO2) was prepared by photo-deposition method according to the previous literature [23]. An aqueous solution (400 mL) containing TiO2 (4.0 g, ST01), K2PtCl6 (40–400 mg), and 2-propanol (3.06 mL) was introduced reaction vessel, which was large scale of cylindrical flask with 35 cm of height and 9.0 cm of diameter. After the oxygen was purged by N2 gas bubbling for 20 min, the solution was irradiated by stirring. After irradiation for 24 h, the water was entirely removed from the reaction mixture by an evaporator. The resulting black precipitate was washed with water on a filter and then dried under reduced pressure to produce Pt/TiO2 [14]. The Pt content on TiO2 was optimized to be 2.0 wt% by the comparison of the H2 amounts evolved from photocatalytic reaction using
3.4 Photocatalytic H2 production
Pt/TiO2 (100 mg) and the given amounts of aqueous solution of sacrificial agent were introduced to reaction vessel. The volume of the reaction solution was adjusted to 150 mL with water. Oxygen was purged from reaction vessel by N2 gas for 20 min. TiO2 was suspended in aqueous solution by vigorous stirring during the irradiation. Total volume of the evolved gas was measured by a measuring cylinder. Irradiation was performed until the gas evolution ceased. The evolved gas (0.5 mL) was taken through rubber tube using syringe and was subjected to the quantitative analysis of H2, N2, CH4, and CO2. Gas analysis was performed on a Shimadzu GC-8A equipped with TCD detector at temperature raised from 40 to 180°C using a stainless column (3 mmΦ, 6 m) packed with a SHINCARBON ST (Shimadzu).
In order to determine the quantum yield (
4. Results
4.1 Sacrificial H2 production using glycerol (1a ) and methanol (1b )
Sacrificial H2 production was applied to
The intercept of the plot equaled the limiting amount of H2 (
Sacrificial agents | Formula | Products/mol mol−1 | Yield/% b | ||||
---|---|---|---|---|---|---|---|
Alcohols | |||||||
Glycerol ( |
C3H8O3 | 7 | 7.2 | 3.1 | 103 | 0.078 | |
Methanol ( |
CH4O | 3 | 3.0 | 1.0 | 100 | 0.057 | |
1-Hydroxy-2-propanone ( |
C3H6O2 | 7 | 4.9 | 2.5 | 0.30 | 87 | 0.045 |
1,2-Propanediol ( |
C3H8O2 | 8 | 4.8 | 1.0 | Trace | 60 | |
1,3-Propanediol ( |
C3H8O2 | 8 | 4.2 | 0.5 | 53 | ||
1-Propanol ( |
C3H8O | 9 | 4.1 | 1.0 | 46 | 0.069 | |
2-Propanol ( |
C3H8O | 9 | 1.3 | 0.0 | 14 | ||
Carboxylic acids | |||||||
Glycolic acid ( |
C2H4O3 | 3 | 2.8 | 1.8 | 93 | ||
Oxalic acid ( |
C2H2O4 | 1 | 1.0 | 2.0 | 100 | ||
Formic acid ( |
CH2O2 | 1 | 1.0 | 1.0 | 100 | ||
Acetic acid ( |
C2H4O2 | 4 | 2.9 | 1.7 | 0.27 | 100 | |
Pyruvic acid ( |
C3H4O3 | 5 | 3.9 | 2.7 | 0.30 | 102 | |
Lactic acid ( |
C3H6O3 | 6 | 4.1 | 2.3 | 0.30 | 88 | |
Malonic acid ( |
C3H4O4 | 4 | 2.6 | 2.7 | 0.31 | 96 | |
Propanoic acid ( |
C3H6O2 | 7 | 2.3 | 1.0 | 33 |
4.2 Degradation mechanism of 1a and 1b
Generally, hydroxyl radical can abstract hydrogen atom more efficiently from the hydroxylated carbon rather than the non-hydroxylated carbon. Therefore, degradation of alcoholic sacrificial agents proceeds through hydrogen-atom abstraction by hydroxyl radical from the hydroxylated alkyl group [Eq. (5)] [15]. Hydroxyl radical reacts with the secondary alcohols to produce ketones, which does not undergo further degradation. The primary alcohols reacted with hydroxyl radical to produce aldehyde, which undergoes further oxidation to carboxylic acid [Eq. (6)]. Furthermore, H abstraction from carboxylic acid by hydroxyl radical induces decarboxylation from carboxylic acids through the formation of carboxyl radical (RCO2·) [Eq. (7)]. When hydroxyl group was substituted on α-position of carboxylic acid [X = OH in Eq. (7)], the decarboxylation took place more smoothly. Many researchers proposed that the decomposition of carboxylic acids is initiated by hole transfer to the carboxylic group rather than H abstraction by hydroxyl radicals [26, 27, 28, 29]. Thus, the degradation of alcohols proceeds through the formation of carboxylic acids:
In 2009, Kondarides et al. reported sacrificial H2 production from
We thought that degradation of
According to Eqs. (5)–(7), a possible degradation mechanism of
4.3 Structural dependence on H2 yields in sacrificial H2 production using several alcohols (1c –1g )
In order to elucidate the relationship between molecular structure of sacrificial agents and degradation yield, sacrificial H2 production was performed using propane-based alcohols such as 1-hydroxy-2-propanone (
Sacrificial H2 evolution using
It was thought that pyruvic acid (
The next sacrificial H2 production was examined using
In sacrificial H2 production using
Moreover, sacrificial H2 production was applied to
Based on these results, the degradation pathways of
4.4 Separation of residual glycerol and methanol in BDF synthesis
Vegetable oil was mainly composed of the oleic acid (C17H33CO2H) triglyceride whose average molecular weight was thought to be 884 g/mol. At first, since carboxylic acid was included in used oil as impurity, the amounts of NaOH (
Vegetable oil (150 mL, 136.5 g, 0.154 mol) was set in a reaction vessel. Since usual optimal amount for transesterification of neutral lipid is known to be 3.55 g/kg [11], the amount of NaOH necessary to the transesterification was determined to be 0.485 g (=0 + 0.485 g) by the sum of
Follow-up operation is shown in Figure 7. After cooling, the reaction mixture was separated into a lower layer and an upper layer. The lower layer (solution A) contained
GLC analysis showed that solution A contained
4.5 Hydrogen production from residual methanol and glycerol in BDF synthesis
The photocatalytic reforming of
Next, photocatalytic reforming was performed with solution B containing
Total amount of H2 from solutions A and B was calculated to be 1.56 mol by Eq. (13) using 0.113 mol of
5. Conclusion and perspective
Sacrificial H2 production can produce H2 in aqueous solutions. Gaseous H2 can be spontaneously isolated from reaction mixture without being separated. Therefore, sacrificial H2 production will provide a promising approach in the utilization of
Recent trends are shifting to the development of solar light-responsive photocatalysts. For example, nanotube-type Pt-N/TiO2 (1 wt% Pt) was applied to sacrificial H2 production with
BDF market has significantly increased to adhere to energy and climate policies [45]. If H2 is produced by a photocatalytic process using solar energy and biomass-derived sacrificial agents, it will be the most promising process to construct clean BDF synthesis.
References
- 1.
Navarro M, Peña MA, Fierro JLG. Hydrogen production reactions from carbon feedstocks: Fossil fuels and biomass. Chemical Reviews. 2007; 107 :3952-3991 - 2.
Yasuda M, Ishii Y, Ohta K. Napiergrass ( Pennisetum purpureum Schumach) as raw material for bioethanol production: Pretreatment, saccharification, and fermentation. Biotechnology and Bioprocess Engineering. 2014;19 :943-950 - 3.
Yasuda M, Takenouchi Y, Nitta Y, Ishii Y, Ohta K. Italian ryegrass ( Lolium multiflorum lam) as a high potential bio-ethanol resource. Bioenergy Research. 2015;8 :1303-1309 - 4.
Ma F, Hanna MA. Biodiesel production: A review. Bioresource Technology. 1999; 70 :1-15 - 5.
Iulianelli A, Seelam PK, Liguori S, Longo T, Keiski R, Calabr V, et al. Hydrogen production for PEM fuel cell by gas phase reforming of glycerol as byproduct of bio-diesel. The use of a Pd–Ag membrane reactor at middle reaction temperature. International Journal of Hydrogen Energy. 2011; 36 :3827-3834 - 6.
Fernández Y, Arenillas A, Díez MA, Pis JJ, Menéndez JA. Pyrolysis of glycerol over activated carbons for syngas production J. Journal of Analytical and Applied Pyrolysis. 2009; 84 :145-150 - 7.
Valliyappan T, Ferdous D, Bakhshi NN, Dalai AK. Production of hydrogen and syngas via steam gasification of glycerol in a fixed-bed reactor. Topics in Catalysis. 2008; 49 :59-67 - 8.
Wang C, Dou B, Chen H, Song Y, Xu Y, Du X, et al. Hydrogen production from steam reforming of glycerol by Ni–Mg–Al based catalysts in a fixed-bed reactor. Chemical Engineering Journal. 2013; 220 :133-142 - 9.
Ngo TA, Sim SJ. Dark fermentation of hydrogen from waste glycerol using hyperthermophilic eubacterium Thermotoga neapolitana . Environmental Progress & Sustainable Energy. 2012;31 :466-473 - 10.
Costa JB, Rossi DM, De Souza EA, Samios D, Bregalda F, Do Carmo M, et al. The optimization of biohydrogen production by bacteria using residual glycerol from biodiesel synthesis. Journal of Environmental Science and Health, Part A. 2011; 46 :1461-1468 - 11.
Yasuda M, Kurogi R, Tomo T, Shiragami T. Hydrogen production from residual glycerol from biodiesel synthesis by photocatalytic reforming. Journal of the Japan Institute of Energy. 2014; 93 :710-715 - 12.
Fujishima A, Rao TN, Tryk DA. Titanium dioxide photocatalysis. Journal of Photochemistry and Photobiology C. 2000; 1 :1-21 - 13.
Galinska A, Walendziewski J. Photocatalytic water splitting over Pt-TiO2 in the presence of sacrificial agents. Energy & Fuels. 2005; 19 :1143-1147 - 14.
Yasuda M, Matsumoto T, Yamashita T. Sacrificial hydrogen production over TiO2–based photocatalysts: Polyols, carboxylic acids, and saccharides. Renewable and Sustainable Energy Reviews. 2018; 81 :1627-1635 - 15.
Shiragami T, Tomo T, Matsumoto T, Yasuda M. Structural dependence of alcoholic sacrificial agents on TiO2-photocatalytic hydrogen evolution. Bulletin of the Chemical Society of Japan. 2013; 86 :382-389 - 16.
Atkins PW. Physical Chemistry. 5th ed. Oxford, UK: Oxford University Press; 1994. pp. 922-926 - 17.
Shimura K, Yoshida H. Heterogeneous photocatalytic hydrogen production from water and biomass derivatives. Energy & Environmental Science. 2011; 4 :467-481 - 18.
Yasuda M. Chapter 19: Photocatalytic reforming of lignocelluloses, glycerol, and chlorella to hydrogen. In: Jacob-Lopes E, Zepka LQ , editors. Frontiers in Bioenergy and Biofuels. Rijeka, Croatia: Intech; 2017. pp. 391-406 - 19.
Yasuda M, Kurogi R, Tsumagari H, Shiragami T, Matsumoto T. New approach to fuelization of herbaceous lignocelluloses through simultaneous saccharification and fermentation followed by photocatalytic reforming. Energies. 2014; 7 :4087-4097 - 20.
Yasuda M, Takenouchi MY, Kurogi R, Uehara S, Shiragami T. Fuelization of Italian ryegrass and Napier grass through a biological treatment and photocatalytic reforming. Journal of Sustainable Bioenergy Systems. 2015; 5 :1-9 - 21.
Shiragami T, Tomo T, Tsumagari H, Ishii Y, Yasuda M. Hydrogen evolution from napiergrass by the combination of biological treatment and a Pt-loaded TiO2-photocatalytic reaction. Catalysts. 2012; 2 :56-67 - 22.
Yasuda M, Hirata S, Matsumoto T. Sacrificial hydrogen production from enzymatic hydrolyzed chlorella over a Pt-loaded TiO2 photocatalyst. Journal of the Japan Institute of Energy. 2014; 95 :599-604 - 23.
Kennedy JC III, Datye AK. Photochemical heterogeneous oxidation of ethanol over Pt/TiO2. Journal of Catalysis. 1998; 179 :375-389 - 24.
Salas SE, Rosales BS, de Lasa H. Quantum yield with platinum modified TiO2 photocatalyst for hydrogen production. Applied Catalysis B: Environmental. 2013; 140-141 :523-536 - 25.
Yasuda M, Kurogi R, Matsumoto T. Quantum yields for sacrificial hydrogen generation from saccharides over a Pt-loaded TiO2 photocatalyst. Research on Chemical Intermediates. 2015; 42 :3919-3928 - 26.
Gu Q , Fu X, Wang X, Chen S, Leung DY, Xie X. Photocatalytic reforming of C3- polyols for H2 production. Part II. FTIR study on the adsorption and photocatalytic reforming reaction of 2-propanol on Pt/TiO2. Applied Catalysis. B, Environmental. 2011; 106 :689-696 - 27.
Slamet Tristantini D, Valentina Ibadurrohman M. Photocatalytic hydrogen production from glycerol-water mixture over Pt-N-TiO2 nanotube photocatalyst. International Journal of Energy Research. 2013; 37 :1372-1381 - 28.
Fu X, Long J, Wang X, Leung Y, Ding Z, Wu L, et al. Photocatalytic reforming of biomass: A systematic study of hydrogen evolution from glucose solution. International Journal of Hydrogen Energy. 2008; 33 :6484-6489 - 29.
Gomathisankar P, Yamamoto D, Katsumata H, Suzuki T, Kaneco S. Photocatalytic hydrogen production with aid of simultaneous metal deposition using titanium dioxide from aqueous glucose solution. International Journal of Hydrogen Energy. 2013; 38 :5517-5524 - 30.
Daskalaki VD, Kondarides DI. Efficient production of hydrogen by photo-induced reforming of glycerol at ambient conditions. Catalysis Today. 2009; 144 :75-80 - 31.
Panagiotopoulou P, Karamerou EE, Kondarides DI. Kinetics and mechanism of glycerol photo-oxidation and photo-reforming reactions in aqueous TiO2 and Pt/TiO2 suspensions. Catalysis Today. 2013; 209 :46-48 - 32.
Daskalaki VM, Panagiotopoulou P, Kondarides DI. Production of peroxide species in Pt/TiO2 suspensions under conditions of photocatalytic water splitting and glycerol photoreforming. Chemical Engineering Journal. 2011; 170 :433-439 - 33.
Slamet R, Gunlazuardi J, Dewi EL. Enhanced photocatalytic activity of Pt deposited on titania nanotube arrays for the hydrogen production with glycerol as a sacrificial agent. International Journal of Hydrogen Energy. 2017; 42 :24014-24025 - 34.
Bowker M, Davies PR, Al-Mazroai LS. Photocatalytic reforming of glycerol over gold and palladium as an alternative fuel source. Catalysis Letters. 2009; 128 :253-255 - 35.
Li Y, Lu G, Li S. Photocatalytic hydrogen generation and decomposition of oxalic acid over platinized TiO2. Applied Catalysis, A: General. 2001; 21 :179-185 - 36.
Li Y, Lu G, Li S. Photocatalytic production of hydrogen in single component and mixture systems of electron donors and monitoring adsorption of donors by in situ infrared spectroscopy. Chemosphere. 2003; 52 :843-850 - 37.
Mozia S, Heciak A, Morawski AW. The influence of physico-chemical properties of TiO2 on photocatalytic generation of C1-C3 hydrocarbons and hydrogen from aqueous solution of acetic acid. Applied Catalysis. B, Environmental. 2011; 104 :21-29 - 38.
Zheng X-J, Wei L-F, Zhang Z-H, Jiang Q-J, Wei Y-J, Xie B, et al. Research on photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV irradiation. International Journal of Hydrogen Energy. 2009; 34 :9033-9041 - 39.
Yasuda M, Tomo T, Hirata S, Shiragami T, Matsumoto T. Neighboring hetero-atom assistance of sacrificial amines to hydrogen evolution using Pt-loaded TiO2-photocatalyst. Catalysts. 2014; 4 :162-173 - 40.
Yu J, Hai Y, Jaroniec M. Photocatalytic hydrogen production over CuO-modified titania. Journal of Colloid and Interface Science. 2011; 357 :223-228 - 41.
Luo N, Jiang Z, Shi H, Cao F, Xiao T, Edwards PP. Photo-catalytic conversion of oxygenated hydrocarbons to hydrogen over heteroatom-doped TiO2 catalysts. International Journal of Hydrogen Energy. 2009; 34 :125-129 - 42.
Petala A, Ioannidou E, Georgaka A, Bourikas K, Kondarides DI. Hysteresis phenomena and rate fluctuations under conditions of glycerol photo-reforming reaction over CuOx/TiO2 catalysts. Applied Catalysis. B, Environmental. 2015; 178 :201-209 - 43.
Pai MR, Banerjee AM, Rawool SA, Nayak C, Ehrman SH, Tripathi AK, et al. A comprehensive study on sunlight driven photocatalytic hydrogen generation using low cost nanocrystalline Cu-Ti oxides. Solar Energy Materials & Solar Cells. 2016; 154 :104-120 - 44.
Wang C, Cai X, Chen Y, Cheng Z, Luo X, Mo S, et al. Efficient hydrogen production from glycerol photoreforming over Ag2O-TiO2 synthesized by a sol-gel method. International Journal of Hydrogen Energy. 2017; 42 :17063-17074 - 45.
Onwudili JA, Williams PT. Catalytic pyrolysis of low-density polyethylene over alumina-supported noble metal catalysts. Fuel. 2010; 89 :501-509