(A) Schematic diagram of gas-phase hydrothermal synthesis of metal phosphide, and scanning electron microscope pictures of the synthesized Ni2P / CFC and Cu3P / CFC; (B) The output of furfural electrocatalytic conversion products and the remaining amount of reactants change with time under two-electrode system Schematic diagram of furfural electrocatalytic conversion under two-electrode system; (C) Mass spectrogram of furfural and furfuryl alcohol; (D) Schematic diagram of the competition between electrocatalytic hydrogenation and electrocatalytic hydrogen evolution
With the declining of traditional fossil energy sources such as coal and petroleum, and the increasingly prominent environmental pollution problems, countries around the world are actively trying to develop new sustainable energy conversion and storage systems. Among them, biomass is an important renewable resource, and its effective development and utilization has been regarded by countries as an important way to replace fossil energy in the preparation of fuels and chemicals.
Recently, the research team of Zhang Haimin, Institute of Solid Physics, Institute of Material Science, Hefei Academy of Sciences, Chinese Academy of Sciences realized the green electrocatalytic conversion of biomass platform molecule furfural to a high value-added chemical process, which is of guiding significance for the design of related efficient catalysts and catalytic reaction systems , Related research results were published in "Applied Catalysis B: Environment".
Biomass resources need to be developed and utilized
Global biomass resource reserves are very rich. According to the report of the US Department of Agriculture and the European Commission, the total amount of agricultural and forestry residues in the world is calculated in terms of energy density, which is basically equivalent to the global consumption of fuel oil. The biomass resources currently produced in the world each year are about billions of tons, but only a relatively small part of them has been developed and utilized, and most of the rest are burned or naturally degraded. This not only causes a great waste of biomass energy, but also the greenhouse gases and dust particles emitted will also cause harm to the environment. Therefore, how to realize the conversion from cheap biomass to fuel and fine chemicals at low cost has always been one of the research hotspots of scientists.
Zhang Haimin, a researcher at the Institute of Solid State Physics, Hefei Academy of Material Sciences, Chinese Academy of Sciences, told the China Science Journal that since 2000, many countries in the world have formulated plans for the use of birth materials.
"For example, the United States plans to obtain more than 20% of liquid fuel and more than 25% of organic chemicals from biomass in 2030; the European Union proposes that bio-based fuels will account for more than 20% by 2020; Japan, India and other countries have also formulated Sunshine plan, green energy plan, etc. "
As a large agricultural country, China has abundant biomass resources, and the total amount of biomass resources available each year is about 460 million tons of standard coal. "Among them, mainly agricultural and forestry waste (lignocellulose), China published the" Renewable Energy Medium and Long-Term Development Plan "and" Renewable Energy 'Twelfth Five-Year Development Plan' "in 2007 and 2011, respectively, and clearly proposed development The route and goal of using biomass energy. And from the perspective of the long-term consumption of the earth ’s resources, the research on the effective recycling method of biomass-based organic carbon resources is of great significance to the protection of the earth ’s environment and resources. â€
Biomass conversion requires new strategies
With the deepening of understanding of biomass resources, the emphasis was on the energy attributes of biomass, and the utilization of renewable organic carbon resource attributes of biomass has been unable to meet the current needs. For this reason, based on the fossil resource conversion method, people have tried to pyrolyze the biomass to develop and utilize its organic carbon resource properties, but because of the high cost, there are few industrialized projects that are really mature and put into production.
After this round of attempts, everyone gradually realized that the conversion technology transplanted from the petrochemical energy conversion process is not suitable for the direct conversion and utilization of biomass.
"This is determined by the nature of the resource. Unlike the molecular structure of fossil resources, which is dominated by CC bonds and CH bonds, the molecular structure of biomass is dominated by CO bonds." Zhang Haimin emphasized that if you want to develop the use of biomass, you must study Innovative transformation strategy, directional shearing and transformation of the basic structural units of biomass, obtaining part of the hydrocarbon and oxygen structural groups, and preparing high value-added chemicals.
The first author of the paper, Dr. Zhang Xian, said that furanaldehyde compounds derived from cellulose (such as furfural and 5-hydroxymethylfurfural) are important biomass platform molecules, which are catalytically converted into high value-added chemicals. The process is to achieve selective C = O bond or furanaldehyde ring-opening hydrogenation reaction, CO bond hydrocracking reaction, selective C = O bond oxidation reaction, etc.
Currently, most of the biomass platform molecular catalytic hydrogenation or oxidation upgrade research is mainly a common thermal catalytic conversion method. This method needs to be carried out under high temperature and high pressure hydrogen conditions. Not only does it require higher energy consumption, but also the conversion rate and selection Sex is very low. In addition, many catalysts and solvents are toxic and will pollute the environment. Therefore, how to promote the biomass platform molecules to a larger range of applications is still a very challenging problem.
Green electrochemical synthesis
In recent years, green electrochemical synthesis methods have received more and more attention in the field of biomass conversion. Scientists use clean energy to convert natural substances, such as water and biomass, into high-value fuels and chemicals through electrochemical methods. This is regarded as an important way to realize the future renewable clean energy conversion system.
According to reports, compared with traditional biomass conversion methods (thermocatalysis or photocatalysis), green electrocatalytic conversion technology has the following advantages: First, it can replace high-cost hydrogen or organic molecules (such as isopropanol, etc.), Direct use of water as a hydrogen source for transfer hydrogenation avoids the use of more dangerous hydrogen or expensive sacrificial agents; second, it can drive catalytic reactions at room temperature and pressure, without the need for high temperature and high pressure reaction conditions, thereby effectively reducing the conversion process Energy consumption in the third; third, the rate of electrocatalytic synthesis reaction can be adjusted by adjusting the size of the current or the pH value of the solution, and at the same time, the selectivity of the reaction product can be improved; fourth, the electrocatalytic or photoelectric catalytic technology can achieve catalytic hydrogenation reduction The reaction and the oxidation reaction proceed simultaneously, which helps to improve the efficiency of energy conversion and utilization. Fifth, biomass electrocatalytic hydrogenation is also a clean and reliable hydrogen energy storage method, which has huge application prospects.
However, electrocatalytic hydrogenation also faces many challenges. The active hydrogen atoms (Had) produced by the electrocatalytic process are prone to Heyrovsky and Tafel reactions to produce hydrogen gas, which leads to a lower probability of the Had atoms reacting with the unsaturated groups on the biomass platform molecules, which ultimately leads to the electrocatalytic hydrogenation reaction The Faraday efficiency and conversion efficiency are very low, so a high-efficiency electrocatalyst is needed to increase the selectivity of the electrocatalytic hydrogenation reaction. At the same time, the products of electrocatalytic synthesis are often more complicated. How to design a highly selective catalyst is crucial. Furthermore, since electrocatalytic hydrogenation requires the output of electrical energy, it is necessary to design an efficient electrocatalytic synthesis reaction system and reduce the consumption of electrical energy to achieve an efficient and high Faraday efficiency electrocatalytic hydrogenation process.
"In summary, the key to furfural's electrocatalytic hydrogenation reaction lies in the design of high Faraday efficiency, high catalytic activity, and high selectivity electrocatalytic transfer hydrogenation catalyst." Zhang Haimin concluded.
Zhang Haimin led the team to select the electrocatalytic upgrade process of the important biomass platform molecule "furfural" as the model reaction, using a novel "gas phase hydrothermal method" to construct a high-efficiency catalyst electrode, and then designing a highly efficient electrocatalytic synthesis reaction system to achieve Double electrodes (cathode and anode) are simultaneously electrocatalyzed in a highly efficient synthesis process.
"We convert the electrocatalytic hydrogenation of furfural with high selectivity, high efficiency, and high current density into furfuryl alcohol at the cathode; the electrocatalytic oxidation of furfural to furoic acid at the anode. The isotope labeling method directly proves the electrocatalytic hydrogenation of furfural The hydrogen is derived from the hydrogen atoms in the water. At the same time, the mechanism of high-efficiency electrocatalytic hydrogenation of the exposed crystal face of the catalyst to the furfural is explored through density functional theory calculation. The highly active exposed crystal face of the prepared catalyst has high adsorption The concentration of hydrogen atoms and the high barrier to generate hydrogen inhibit the electrocatalytic hydrogen evolution process, thereby achieving its selectivity for the electrocatalytic hydrogenation of furfural. "(Reporter Zhang Jingjing)
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