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The ring‐rearrangement of 5‐hydroxymethylfurfural (HMF) to 3‐hydroxymethylcyclopentanone (HCPN) was investigated over Ni catalysts supported on different carbon supports and metallic oxides with different structure and acid‐base properties. Their catalytic performance was tested in a batch stirred reactor in aqueous solution at 180 °C and 30 bar of H2. Under these conditions, the HMF hydrogenation proceeds through three possible competitive routes: (i) a non‐water path leading to the total hydrogenation product, 2,5‐di‐hydroxymethyl‐tetrahydrofuran (DHMTHF), and two parallel acid‐catalyzed water‐mediated routes responsible for (ii) ring‐opening and (iii) ring‐rearrangement reaction products. All catalyst systems primarily produced HCPN, but reaction rates and product distribution were influenced by several variables, some of them intensely analyzed in this work. The most proper conditions resulted to be the presence of the medium/strong Lewis's acidity of a Ni/ZrO2 catalyst (initial TOF=5.99 min−1 and 73 % HCPN selectivity) or the Brønsted acidity originated by an oxidized high surface area graphite, Ni/HSAG‐ox (initial TOF=5.92 min−1 and 87 % HCPN selectivity). However, too high density of acidic sites on the catalyst support (Ni/Al2O3) and sulfur impurities from the HMF feedstock led to catalyst deactivation by coke deposition and Ni poisoning, respectively. [ABSTRACT FROM AUTHOR]

Commercial high surface area graphite (HSAG300) and commercial TiO2 were used to produce composite materials through a simple mechanochemical method involving milling and ultrasonic treatments. The acid and basic sites exposed on the surfaces of these materials were characterized by temperature‐programmed desorption (TPD) of ammonia and carbon dioxide. The catalytic materials were tested in the dehydration reaction of formic acid to produce hydrogen‐free CO. While HSAG300 is practically inactive under reaction conditions (continuous gas flow at temperatures in the range of 100–250 °C), all samples containing TiO2 are active, exhibiting high selectivity to CO without significant deactivation at moderate reaction temperatures. It is demonstrated that the presence of graphite in the catalysts enhances the specific catalytic activity of TiO2. Assuming that the dehydration reaction is catalyzed by acid sites on the TiO2 surfaces, a comparative evaluation of the surface sites reveals that the graphite‐TiO2 interactions not only change the density of surface sites but also modify the strength of the acid centers of TiO2. In summary, the interaction of HSAG300 with TiO2 modulates the surface properties of the prepared composite catalysts, decreasing the total number of basic surface sites and increasing the strength of acidic sites compared to bare TiO2. [ABSTRACT FROM AUTHOR]

The condensation of ethanol to 1‐butanol in the presence of different catalyst systems based on a Pd dehydrogenating/hydrogenating component and magnesium hydroxide‐derived materials as basic ingredient was studied in a fixed‐bed reactor. The metal was incorporated by wetness impregnation, and the resulting material was then reduced in situ with hydrogen at 573 K for 1 h before reaction. The bifunctional catalysts were tested in a fixed‐bed reactor operated in the gas phase at 503 K and 50 bar with a stream of helium and ethanol. A bifunctional catalyst supported on a synthetic composite based on Mg and high surface area graphite (HSAG) was also studied. Improved catalytic performance in terms of selectivity towards 1‐butanol and stability was shown by the Pd catalyst supported on the Mg–HSAG composite after thermal treatment in helium at 723 K, presumably due to the compromise between two parameters: adequate size of the Pd nanoparticles and the concentration of strongly basic sites. The results indicate that the optimal density of strongly basic sites is a key aspect in designing superior bifunctional heterogeneous catalyst systems for the condensation of ethanol to 1‐butanol. A good compromise: A high‐performance Pd/MgO bifunctional catalyst for the continuous gas‐phase condensation of bioethanol to 1‐butanol is designed. An optimum compromise between the number of metal atoms and the amount of strongly basic sites exposed on the surface of the catalyst is found to result in the highest 1‐butanol yield. [ABSTRACT FROM AUTHOR]

Abstract: A series of carbon supported polyoxometalates have been prepared and studied as acid catalysts for the fructose dehydration. The catalytic supports, microporous activated carbon (AC, SBET=1190 m2/g) and high surface area graphite (HSAG, SBET=400 m2/g), were loaded with 15 wt% of polyoxometalates: phosphotungstic acid (TPA) or tungstosilicic acid (STA). The four resulting catalysts were tested in the fructose reaction at moderate temperature 140 °C, using water and ethanol solvents. Catalytic properties have been compared with those of an acidic resin, Amberlyst 15. As relevant findings the specific interactions of carbon supports and polyoxometalates let the inhibition of active phase lixiviation. An improved catalyst (STA‐HSAG) in terms of selectivity to valuable products (ethoxymethylfurfural and ethyl levulinate) and high specific catalytic activity using ethanol as solvent has been developed. This catalyst can be reused after regeneration by washing with organic solvents. [ABSTRACT FROM AUTHOR]

For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties. [ABSTRACT FROM AUTHOR]

Oxygen surface groups, which are typically present on the surface of activated carbon, have a decisive effect on the achieved dispersion of active phases, which affects the electronic properties of the surface sites and stabilizes the materials against sintering phenomena. Therefore, the desorption of oxygen surface groups during the decomposition-reduction of the metal salt precursors of the fresh carbon-based catalysts can lead to surface reconstruction of the metal nanoparticles, which can significantly affect their catalytic activity. In this work, the oxidation states of Ru atoms supported on both an activated carbon thermally treated to remove all oxygen groups and the untreated material were studied during the reduction process. The precursor to prepare these catalysts is Ru(NO)(NO3)3. The main results were obtained by using in situ X-ray absorption near-edge structure analysis of the Ru K-edge under conditions comparable to the temperature-programmed reduction experiments. The different reduction mechanism observed in each of the catalysts, of a multistep nature if oxygen surface groups are present and single-step in the case of clean graphitic surfaces, can be regarded as a typical metal-support interaction. Moreover, differences in both the final Ru oxidation state and the subsequent interaction of the active phase with the support are the main cause of the five-times higher catalytic activity observed in the presence of the catalyst without surface oxygen groups for the NH3 decomposition reaction. [ABSTRACT FROM AUTHOR]