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Ni–Al hydrotalcite-like compounds (Ni–Al HTLCs) containing nitrate anions were synthesized and applied in the acetalization of p-anisaldehyde with ethylene glycol under mild reaction conditions. The Ni–Al HTLCs showed good selectivity for acetalization and achieved almost complete conversion of p-anisaldehyde. The Ni–Al HTLCs as water-tolerant Lewis acids were proved to be an efficient and recyclable catalyst for the acetalization. The oxygen vacancies play an important role in the catalytic activity of Lewis acidic sites on the surface of Ni–Al HTLCs. The NO3− anions coordinate to the matrix Ni2+ cations through oxygen atoms to form [Ni(OH)5NO3] units in the distorted octahedral crystal field, and the most oxygen vacancies in freshly-prepared Ni–Al HTLCs result from the strongly distorted [Ni(OH)5NO3] units. The gradual conversion of distorted [Ni(OH)5NO3] units into regular [Ni(OH)6] units will lead to a loss in catalytic activity of Ni–Al HTLCs. [ABSTRACT FROM AUTHOR]

Abstract The Cu/ZnO/Al 2 O 3 catalysts (CuZnAl) can be utilized to directly synthesize higher alcohols from syngas under mild conditions. Carbon fibers (CFs) are widely used as a catalyst supporter, and potassium is usually used as a good electron assistant for charge transfer to the active phase of the catalyst. However, little is known about the combined effects of CFs and potassium on Cu/ZnO/Al 2 O 3 catalysts. In this work, the CuZnAl catalysts supported on activated carbon fibers (ACFs) were prepared by a co-precipitation method, and then the catalysts were modified by potassium. The catalytic performances of K-modified CuZnAl and composites containing ACFs and CuZnAl were evaluated. Addition of ACFs and/or potassium increased CO conversion and selectivity for isobutanol compared with pure CuZnAl. All the samples were characterized by BET, XRD, SEM–EDS, CO–TPD, and Raman spectroscopy to further disclose the reason for better catalytic performance of the catalysts with ACFs and/or potassium. We found that addition of ACFs or potassium promotes moderate CO adsorption and formation of the active phase (CuO/ZnO solid solution) during alcohol synthesis, which facilitates synthesis of higher alcohols and CO conversion. As a result, ACFs and potassium exhibited synergistic effects on improvement of CO conversion and selectivity for isobutanol. Graphical abstract Image Highlights • Carbon fibers improve dispersion of Cu/ZnO/Al 2 O 3 nanoflakes. • Carbon fibers and potassium promote formation of CuO/ZnO solid solution. • Carbon fibers and potassium enhance moderate CO adsorption. • Potassium and carbon fibers have synergistic effects on isobutanol synthesis. [ABSTRACT FROM AUTHOR]

The Cu/ZnO/Al 2 O 3 catalysts (CuZnAl) can be utilized to directly synthesize isobutanol from syngas at low temperatures, and complexants are new and efficient modifiers for the catalysts used to synthesize higher alcohols. However, little is known about effects of the complexants such as ethylene diamine tetra-acetic acid (EDTA) and triethanolamine (TEA) on structure and catalytic activity of CuZnAl. In this work, the precursors of CuZnAl, hydrotalcite-like compounds (HTLCs), were treated with EDTA and TEA to obtain the CuZnAl modified by EDTA (CuZnAl-EDTA) and TEA (CuZnAl-TEA). The catalytic performances of CuZnAl, CuZnAl-EDTA and CuZnAl-TEA were evaluated. Addition of EDTA or TEA increased CO conversion and selectivity for isobutanol and ethanol compared with pure CuZnAl. All the samples were characterized by BET, XRD, SEM, CO–TPD, CO 2 –TPD, H 2 –TPR and FTIR spectroscopy to further disclose the reason for better catalytic performance of CuZnAl-EDTA and CuZnAl-TEA. We found that the EDTA and TEA promote reduction of CuO, increase in concentration of basic sites and formation of floccule-like structure, which efficiently improves catalytic activity of CuZnAl-EDTA and CuZnAl-TEA for synthesis of isobutanol and ethanol. However, EDTA restrains CO desorption from the surface of the catalysts, and thus the strongly adsorbed CO molecules may lead to lower catalytic activity of CuZnAl-EDTA compared with CuZnAl-TEA. [ABSTRACT FROM AUTHOR]

Benzoin methyl ether (BME) is an important photosensitizer for coatings and printing technologies, and Cu/Cr hydrotalcite-like compounds (CuCr-HTLcs) is promising to be used as pollution-free catalyst for BME synthesis. However, little is known about effect of CuCr-HTLcs structure on catalytic synthesis of BME. In this work, a series of CuCr-HTLcs with different ratios of Cu to Cr (n Cu /n Cr ) was successfully prepared by a co-precipitation method. The structure of CuCr-HTLcs were systematically characterized. The copper and chromium in CuCr-HTLcs mainly exist in the form of Cu 2+ and Cr 3+ , respectively. The n Cu /n Cr has significant effects on crystallinity, acidity, and textural properties of CuCr-HTLcs. Subsequently, catalytic performance of CuCr-HTLcs was tested for BME synthesis. We found that BME synthesis is mainly influenced by combined effects of acid-site concentration and pore size. Moderate acid-site concentration and pore size (mesopores) are the critical factors for improving catalytic activity of CuCr-HTLcs and BME selectivity. [ABSTRACT FROM AUTHOR]

Oxygen-containing functional groups and mineral matter play important roles in thermal conversion of brown coals, but little attention has been paid to the effects of mineral matter on the conversion kinetics of oxygen-containing functional groups. In this work, silicon-containing mineral compounds (quartz and clays) and cations were removed by treatments of HF and HCl aqueous solutions, respectively. Thereafter, curve-fitting technique was used to analyze spectra measured by in-situ diffuse reflectance infrared Fourier transformation (DRIFT) technique during pyrolysis. The results show that first-order kinetic model is suitable for describing elimination of carboxylic acids and their derivatives, but formation of some compounds, such as anhydrides and phenolic esters of aliphatic acids (RCOOAr), accords with kinetic model with higher reaction order (two or three). Cations catalyze the decomposition of carboxylic dimers and thus promote the formation of anhydrides and RCOOAr, resulting in small decrease in amounts of anhydrides and RCOOAr at high temperatures. Clays and quartz (CAQ) restrain the elimination of carboxylic acids and their derivatives by impeding diffusion of volatile matters outwards into surrounding atmosphere. CAQ also suppress the formation of RCOOAr by obstructing contact among oxygen-containing functional groups. [ABSTRACT FROM AUTHOR]