• Energy Research

Rhenium is an effective promoter for ZnO catalysts in glycerol hydrogenolysis by enhancing catalytic activity and producing lower alcohols in good yields.

Abstract Pt supported on TiO2 and ZrO2 catalysts were synthesized via wet impregnation and deposition precipitation methods. The catalysts were tested for CO removal from reformate gas following the water-gas shift reaction for on-board fuel processors. Tests included oxidation of CO to CO2, preferential oxidation of CO to CO2 in the presence of H2 (PROX), and hydrogenation of CO to CH4 (selective methanation, SMET). The Pt–ZrO2 catalysts showed better metal dispersions, particle sizes, lower degrees of reduction and higher oxygen storage capacities than the TiO2 supported catalysts. All catalysts showed low activity for the oxidation of CO in the PROX reaction, due to H2 and O2 spillover effects. ZrO2, with its high reducing properties and strong metal-support interactions, was found to be the best support for hydrogenation of CO. ZrO2 induced small well-dispersed Pt particles that were key parameters in this reaction. Both Pt–ZrO2 catalysts showed CO conversions over 99% above 350 °C with high CH4 selectivities (99%). The study shows advantageous effects of strong metal to support interactions, like participation of MOx (support) species in activating the CO molecule. The CO concentration was effectively reduced to the desired ppm levels (

Incorporation of Re in supported Ni catalysts greatly improves hydrogenolysis of glycerol to mono-alcohols via increased acidity, dispersion and metal–support interaction.

AbstractMonometallic 50 wt % Cu/Al2O3 catalyst and bimetallic catalysts containing 25 wt % Co/25 wt % Cu, 25 wt % Co/25 wt % Fe, and 25 wt % Cu/25 wt % Fe, supported on Al2O3, were prepared by impregnation and coimpregnation methods. For bimetallic catalysts, metal oxides were in the form of spinel oxides, which exhibited a strong metal–support interaction. The decomposition of methane over these catalysts led to the formation of pure hydrogen and carbon nanotubes on their surfaces. The activation energy, total carbon yield, and amount of hydrogen formed, by using the prepared catalysts, were in agreement with the metal dispersion and acid–base site ratio on the surface of the catalysts. Cu−Fe/Al2O3 catalyst exhibited a stable hydrogen formation rate of 58 mmol min−1 g−1 at a temperature of 650 °C. All catalysts exhibited deactivation after 500 min, which occurred due to the formation of carbon on the surface of the catalysts. The carbon material deposited predominantly assumed the form of multiwalled carbon nanotubes, as evidenced by high‐resolution TEM and Raman spectroscopy. Thermogravimetric analysis finally confirmed that Cu−Fe/Al2O3 exhibited a higher yield of multiwalled carbon nanotubes.

Abstract Catalytic conversion performance of the γ-Al2O3-supported Cu-, Mn- and Ni-based materials for the selective preferential oxidation of CO was investigated. The influence of CO2 and H2O in the reactor feed gas on activity and selectivity was lastly investigated for copper bimetallic catalysts containing manganese and nickel. Cu/Al2O3 proved to be optimal among the monometallic examined. It was observed that even in the absence of H2, CO was effectively converted. Upon H2 presence, a fraction of oxygen is utilized for the latter, which results in the decrease of CO turnover. Cu–Mn/Al2O3 surpassed other single and mixed metal oxide catalysts which could be due to a combination of surface desorption capacity and redox properties. The oxygen storage capacities (OSC) were in the order of Cu–Mn/Al2O3 > Cu–Ni/Al2O3 > Cu/Al2O3 > Mn/Al2O3 > Ni/Al2O3, in an agreement with reactivity. The efficiency at low process temperatures was enhanced by adding H2O vapors, nonetheless, decreased at high-end range due to the reverse water–gas shift (RWGS). Also, the rate of CO conversion was high utilizing Cu–Mn/Al2O3; furthermore, even upon applying H2O and CO2. CO2 notably affected CO conversion, and ultimately, decreased the activity, which, conversely, remained stable upon time-on-stream.

Abstract Transition metal carbides and nitrides with large surface areas are attractive for various catalytic reactions. The synthesis of molybdenum carbide, molybdenum nitride and nanocomposite mixed-phase nanowires with the preserved structural morphology of two different precursor reactant materials by heating in diverse gas mixtures is reported herein. Prepared heterogeneous catalysts were characterized using diffraction, physisorption, chemisorption and microscopic techniques. With XRD and interfacial elemental analysis, performed by a transmission electron microscope, the composition of starting intermediate moieties and products was determined. Ordered grain structure appeared almost independent of applied gaseous compounds and typical domain sizes were comparable. The conversions of CO2 during the reverse water–gas shift (RWGS) were calculated for all measured samples in a wide operation range. Composite Mo2C/Mo2N showed the highest conversion higher than the pure Mo2C with similar site amount and especially larger than Mo2N, which demonstrated a low activity throughout the process. The stability of Mo2C/Mo2N wires was tested at 300 °C and they exhibited an unchanged time-on-stream reactivity over a long period of time (>24 h), withstanding deactivation. In addition, the selectivity towards CO was maintained at around 99%. The comparison of catalyst characterisation before and after RWGS reaction show that there is no major difference in the physical and chemical characteristics of the materials further validate the use of the present catalysts.

Abstract Nanocomposite Cu–Mn–O nano-particle (CuMnNP) and nano-sheet (CuMnNS) catalyst were successfully prepared using a one-step hydrothermal method in the absence of any templating reagent. Materials were characterised applying various structural techniques. SEM images showed that composite Cu–Mn oxide sheets were tailor-made synthesised by a one-pot urea-abetted protocol. Conversely, upon replacing carbamate by Na2CO3, oxidised metal Cu–Mn particles could be obtained. The formation of bulk mixed Cu–Mn phases resulted in an enhanced crystal lattice oxygen reactivity in CuMnNS. XPS, XRD and TPR measurements confirmed the presence of the Cu+ and Cu2+ species in nano-catalysts, and CuMnNS nanomaterials possessed more surface defects, thus causing a higher O2 adsorption/storage capacity. CuMnNS presented a superior catalytic activity as opposed to CuMnNP in the preferential oxidation (PROX) pathway of CO. With both CO2 and H2O in feed, a decrease in CO turnover was observed, due to a competitive interface binding of CO, CO2 and H2O. Compared to CuMnNP, CuMnNS also demonstrated a high time-on-stream conversion of methanol for the reforming for all operating conditions.

Abstract CO2 hydrogenation was carried out over a series of Cu/ZnO/Al2O3 catalysts, which were prepared by different synthesis methods (co-precipitation, ultrasound-assisted, sol-gel and solid-state). The applicative physicochemical properties of the materials and their catalytic performance were investigated. Subsequently, the preparation methodology influence on the average Cu particle size, the interactions of metals, the exposed copper phases surface area and the ratio of Cu0/Cu+, as well as its specific effect on reactions, were assessed in detail. The ultrasonic synthetic route provided increased basic active sites' number and significant methanol selectivity, compared to the conventional precipitation procedure, while it also improved the dispersion of separate Cu metallic particles, which ultimately changed the intrinsic reactive activity of CuO–ZnO. The trend of apparent CH3OH productivity rate was consistent with the Cu+/Cu0 ratio or content as well. The presence of Cu+ species at high concentration levels is thus crucial for high methanol selectivity and an extremely low selectivity towards CO at the conventional industrial operating conditions analysed. The dependence of the selective methanol production on the fraction of determined alkaline moieties was found analogous to all catalysts studied. Cu+/Cu0 oxidation state role and distribution may, therefore, aid in CO2 conversion catalyst design and optimisation.