Research

The increasing emissions of carbon dioxide (CO2) are primarily driven by the rapid expansion of energy-intensive sectors such as the chemical industry. This work selects ethylene, one of the most important chemicals, as a model study to represent the low-carbon roadmap of chemical production. Four strategies improving the efficiency of fossil resource usage, developing the technology for carbon capture and storage (CCS), CO2 chemical conversion, and converting biomass resources into chemicals, are used to reduce CO2 emissions. A comprehensive analysis of the life cycle CO2 emissions of different ethylene production routes has been performed to compare their emission reduction potential. The results indicate that the BMTO (biomass to olefins via methanol-to-olefins) pathway releases the least CO2 (− 1.3 t CO2/t ethylene), while the CFTO (coal to olefins via Fischer-Tropsch synthesis) possesses the highest CO2 emissions. Combining CCS with BMTO results in CO2 emissions of – 8.2 t per t ethylene. Furthermore, we analysed the annual production and CO2 emissions of ethylene in the last 17 years and integrated this real-time change with different pathways. The CO2 emissions have decreased by 29.4% per t ethylene from 2000 to 2016 in China. However, the total amount of CO2 emissions continuously increases in ethylene production industry. Given that China has promised to hit peak CO2 emissions by 2030, a scenario analysis was performed. To achieve this goal, the ratios of BMTO, CO2MTO (CO2 to olefins via methanol-to-olefins) or BETE (ethanol to ethylene pathway originating from biomass) pathways should increase by 1.0%, 1.2% and 1.1% annually from 2020, respectively. Then more than 500 million metric tons of CO2 will be eliminated from 2020 to 2040. The results highlight the pivotal role that regulation and policy administration can play in controlling CO2 emissions by increasing average technological level and turning to low-carbon routes in the chemical industry in China.

Quinazolinones, an important class of heterocyclic compounds, have been widely used in pharmaceuticals because of their biological activity. However, the efficient and economical synthesis of quinazolinones has remained a challenge. A novel synthetic approach has now been developed to produce quinazolinones from olefins, CO, and amines over heterogeneous Ru‐clusters/ceria catalyst in the absence of acids, bases, and oxidants. Furthermore, H2O is generated as the only by‐product. A series of quinazolinones with aromatic or non‐aromatic substituents can be obtained in yields of up to 99 %. The Ru‐clusters/ceria can be reused at least four times. The analysis of the E‐factor (environmental impact factor) for the synthesis of 2‐ethyl quinazolinone suggests that this system is more environmentally friendly than other processes reported previously.

Lignin is a renewable and abundant aromatic polymer found in plants. We herein propose a “cutting tail” methodology to produce phenol from lignin, which is achieved by combining Ru/CeO2 catalyst and CuCl2 oxidant via an oxidation–hydrogenation route. Phenol was obtained from separated poplar lignin with 13 wt % yield. Even raw biomass, such as poplar, birch, pine, peanut, bamboo willow, and straw, could be converted into phenol in 1–33 mg per gram of biomass.

Photocatalysis is a potentially promising approach to harvest aromatic compounds from lignin. However, the development of an active and selective solid photocatalyst is still challenging for lignin transformation under ambient conditions. We herein report a mild photocatalytic oxidative strategy for C–C bond cleavage of lignin β-O-4 and β-1 linkages using a mesoporous graphitic carbon nitride catalyst. Identifications by solid-state NMR techniques and density functional theory (DFT) calculations indicate that π–π stacking interactions are most likely present between the flexible carbon nitride surface and lignin model molecule. Besides, low charge recombination efficiency and high specific surface area (206.5 m2 g–1) of the catalyst also contribute to its high catalytic activity. Mechanistic investigations reveal that photogenerated holes, as the main active species, trigger the oxidation and C–C bond cleavage of lignin models. This study sheds light on the interaction between complex lignin structures and the catalyst surface and provides a new strategy of photocatalytic cleavage of lignin models with heterogeneous photocatalysts.

Valuable polyester monomers and plasticizers—1,4‐cyclohexanedimethanol (CHDM), 1,4‐cyclohexanedicarboxylic acid (CHDA), and 1,2‐cyclohexanedicarboxylates—have been prepared by a new strategy. The synthetic processes involve a proline‐catalyzed formal [3+1+2] cycloaddition of formaldehyde, crotonaldehyde, and acrylate (or fumarate). CHDM is produced after a subsequent hydrogenation step over a commercially available Cu/Zn/Al catalyst and a one‐pot hydrogenation/oxidation/hydrolysis process yields CHDA, whereas 1,2‐cyclohexanedicarboxylate is obtained by a Pd/C‐catalyzed tandem decarbonylation/hydrogenation step.

The interface of metal-oxide plays pivotal roles in catalytic reactions, but its catalytic function is still not clear. In this study, we report the high activity of nanostructured Ru/ceria (Ru-clusters/ceria) in the ethylene methoxycarbonylation (EMC) reaction in the absence of acid promoter. The catalyst offers 92% yield of MP with TOF of 8666 h–1, which is about 2.5 times of homogeneous Pd catalyst (∼3500 h–1). The interfacial Lewis acid–base pair [Ru-O-Ce-Vö], which consists of acidic Ce-Vö (oxygen vacancy) site and basic interfacial oxygen of Ru-O-Ce linkage, acts as active site for the dissociation of methanol and the subsequent transfer of hydrogen to the activated ethylene, which is the key step in acid-promoter-free EMC reaction. The combination of 1H MAS NMR, pyridine-IR and DFT calculations reveals the hydrogen species derived from methanol contains Brönsted acidity. The EMC reaction mechanism under acid-promoter-free condition over Ru-clusters/ceria catalyst is discussed.

Defect chemistries of metal-doped CeO2 catalysts have attracted extensive scientific interests in heterogeneous catalysis. Here, we report the structure–activity relationship of CeO2 catalysts doped by Pr. The Pr-doped CeO2 solid solution catalysts were prepared by a coprecipitation method and evaluated in Prins condensation–hydrolysis of isobutene with formalin to 3-methyl-1,3-butanediol. Raman and infrared (IR) spectroscopies were used to characterize the defect sites of the catalysts. Pr creates two kinds of defects in Pr-doped CeO2: oxygen vacancy and lattice distortion (Pr3+O8-type complex, which was confirmed by the Raman and XPS spectra), whose concentrations depend on the Pr doping amount. The relationship between defect properties (type and concentration) and their catalytic consequence is established. The catalytic performance significantly depends on the oxygen vacancy concentration in Pr-doped CeO2 catalysts. This study also shows that a Pr3+O8-type complex has little effect on the catalytic performance, indicating that the Pr3+O8-type complex is a spectator during the reaction. DFT calculations have indicated that the oxygen vacancy induced by the Pr dopant on a CeO2 surface promotes the adsorption of HCHO and inhibits the adsorption of isobutene, suggesting the condensation of HCHO and isobutene occurs via an Eley–Rideal (ER) mechanism.

Herein, a strategy is developed for efficient production of 1,3-propanediol via the hydrolysis of 1,3-dioxane by the in situ transformation of the co-product formaldehyde (HCHO) in the presence of Eu(OH)3. The reversible hydrolysis reaction is promoted to yield 98% conversion and 99% 1,3-propanediol selectivity. Furthermore, HCHO is converted to formic acid (HCOOH) which could act as an acidic catalyst in the hydrolysis of 1,3-dioxane. The combination of FT-IR and control experiments demonstrates that HCOOH is generated via the hydrolysis of formate species which formed on the surface of Eu(OH)3.

The use of biomass as a resource has developed rapidly in recent years, and various kinds of chemicals could be produced from biomass. Although biomass is annually renewable and abundant, it is important to process it in the most efficient way. Before rushing into biomass conversion, it is necessary to consider what chemicals are reasonably and economically produced from biomass. In this Review, we first analyzed the products from biomass based on the structural properties and economics. Taking into account the oxygen-rich character of the feedstock, it is a reasonable route to convert the biomass into valuable oxygen-containing fine chemicals, among which organic acids are one class of important and widely used fine chemicals. Then, we provided insights into the recent progress in the oxidative cleavage of biomass into organic acids and their derivatives, such as esters and anhydrides. The biomass resources cover the lignocellulose biomass, sugars, chitin, platform molecules, and fats. As biomass resources are generally polymers and the C–C bond is the backbone, the oxidative cleavage of C–C bond can break up the biomass to small molecules and introduce acid functionality at the same time. This Review particularly focuses on the generation of acids via a C–C bond-oxidative-cleavage process. Various methods, catalytic systems, and C–C bond-cleavage mechanisms are summarized. Finally, we conclude with mentioning the challenges in the oxidative conversion of biomass and the possible research direction in this area.

Conversion of lignin to aromatic compounds via C–C/C–O bond cleavage has been an attractive but challenging subject in recent years. We herein report the first protocol that converts lignin models and preoxidized lignin to isoxazole and aromatic nitrile. The isoxazole motif is constructed by condensation of β-hydroxyl ketone with hydroxylamine. Magnesium oxide promotes an oximation reaction and an intramolecular condensation. Aromatic nitriles and esters are obtained via Beckmann rearrangement or an acidolysis reaction depending on the selected additive. The hydroxylamine-mediated strategy works well for the preoxidized lignin conversion to aromatic isoxazole, nitrile, and ester monomers with up to 7.6% yield.

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