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Titania−silica mixed oxides (denoted as TiO2−SiO2) with different Ti contents are prepared by a sol−gel route in the presence of citric acid (CA). Various characterization techniques, including XRD, FT-IR, N2-adsorption, TEM, solid-state CP-MAS NMR spectroscopy, UV−vis, and NH3-TPD, have been carried out to investigate the physical−chemical properties, states of Ti species, and the formation process of TiO2−SiO2 materials. The characterization results show that the TiO2−SiO2 materials possess a mesoporous silicate framework with high specific surface area and thermal stability. Titanium species in the TiO2−SiO2 materials are mainly present in the form of two-dimensional low polymeric TiO x species, which are uniformly dispersed on the surface of mesoporous silica. Additionally, the titanium species have a strong resistence to high-temperature sintering, even for the sample with high Ti contents (25 wt %). Weak acid sites are observed over TiO2−SiO2 materials, and the amount of acidic sites increases with the increment of Ti contents. The acid catalytic performance of TiO2−SiO2 materials is investigated in the transesterification of dimethyl oxalate (DMO) with phenol. All the materials are active for the reaction, and the total selectivity to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) is very high (>99%). The formation mechanism of such materials is discussed concerning the interaction between citric acid and precursors of silicon and titanium. We propose that a portion of CA can act as a ligand to coordinate with titanium species to form the titanium−CA complexes. Both CA and the titanium−CA complexes may act as a template for the formation of a silica framework. After calcination, titanium species release from the titanium−CA complex and reach a position on the surface of silica, forming the resultant TiO2−SiO2 materials.

A series of carbon-supported CaO materials, prepared using different porous carbon materials as supports, were tested as basic catalysts for the transesterification of triacetin with methanol and characterized by means of X-ray diffraction (XRD), N 2 adsorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). It was found that all of the carbon-supported CaO catalysts are active for the transesterification reaction, and their catalytic performance can be influenced by a variety of factors, such as the types of carbon supports, the concentration of impregnated CaO, the heattreated temperatures of the catalysts, and the reaction temperatures. Particularly, the supported CaO catalyst, which is prepared using a kind of porous carbon (NC-2) as a support, exhibits very high activity, stability, and recyclability. We suppose that the main characteristics of this porous carbon, such as the presence of relatively abundant surface oxygen-containing functional groups and well-developed porosity, may be beneficial to build a suitable interaction between CaO particles and the carbon support, thus resulting in the formation of an active and stable catalyst system.

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Plant polysaccharides, a type of important bioactive compound, are involved in multiple plant defense mechanisms, and in particular polysaccharide-alleviated abiotic stress has been well studied. Polygonatum cyrtonema Hua (P. cyrtonema Hua) is a medicinal and edible perennial plant that is used in traditional Chinese medicine and is rich in polysaccharides. Previous studies suggested that sucrose might act as a precursor for polysaccharide biosynthesis. However, the role of sucrose metabolism and transport in mediating polysaccharide biosynthesis remains largely unknown in P. cyrtonema Hua. In this study, we investigated the contents of polysaccharides, sucrose, glucose, and fructose in the rhizome, stem, leaf, and flower tissues of P. cyrtonema Hua, and systemically identified the genes associated with the sucrose metabolism and transport and polysaccharide biosynthesis pathways. Our results showed that polysaccharides were mainly accumulated in rhizomes, leaves, and flowers. Besides, there was a positive correlation between sucrose and polysaccharide content, and a negative correlation between glucose and polysaccharide content in rhizome, stem, leaf, and flower tissues. Then, the transcriptomic analyses of different tissues were performed, and differentially expressed genes related to sucrose metabolism and transport, polysaccharide biosynthesis, and transcription factors were identified. The analyses of the gene expression patterns provided novel regulatory networks for the molecular basis of high accumulation of polysaccharides, especially in the rhizome tissue. Furthermore, our findings explored that polysaccharide accumulation was highly correlated with the expression levels of SUS, INV, SWEET, and PLST, which are mediated by bHLH, bZIP, ERF, ARF, C2H2, and other genes in different tissues of P. cyrtonema Hua. Herein, this study contributes to a comprehensive understanding of the transcriptional regulation of polysaccharide accumulation and provides information regarding valuable genes involved in the tolerance to abiotic stresses in P. cyrtonema Hua.