Ethanol Coupling Reactions over MgO-Al2O3 Mixed Oxide-Based Catalysts for Producing Biofuel Additives.

Catalytic conversion of ethanol to 1-butanol was studied over MgO-Al2O3 mixed oxide-based catalysts. Relationships between acid-base and catalytic properties and the effect of active metal on the hydrogen transfer reaction steps were investigated. The acid-base properties were studied by temperature-programmed desorption of CO2 and NH3 and by the FT-IR spectroscopic examination of adsorbed pyridine. Dispersion of the metal promoter (Pd, Pt, Ru, Ni) was determined by CO pulse chemisorption. The ethanol coupling reaction was studied using a flow-through microreactor system, He or H2 carrier gas, WHSV = 1 gEtOH·gcat.-1·h-1, at 21 bar, and 200-350 °C. Formation and transformation of surface species under catalytic conditions were studied by DRIFT spectroscopy. The highest butanol selectivity and yield was observed when the MgO-Al2O3 catalyst contained a relatively high amount of strong-base and medium-strong Lewis acid sites. The presence of metal improved the activity both in He and H2; however, the butanol selectivity significantly decreased at temperatures ≥ 300 °C due to acceleration of undesired side reactions. DRIFT spectroscopic results showed that the active metal promoted H-transfer from H2 over the narrow temperature range of 200-250 °C, where the equilibrium allowed significant concentrations of both dehydrogenated and hydrogenated products.

Temperature-Limited Synthesis of Copper Manganites along the Borderline of the Amorphous/Crystalline State and Their Catalytic Activity in CO Oxidation.

Copper manganese oxides (CMO) with CuMn2O4 composition are well-known catalysts, which are widely used for the oxidative removal of dangerous chemicals, e.g., enhancing the CO to CO2 conversion. Their catalytic activity is the highest, close to those of the pre-crystalline and amorphous states. Here we show an easy way to prepare a stable CMO material at the borderline of the amorphous and crystalline state (BAC-CMO) at low temperatures (<100 °C) followed annealing at 300 °C and point out its excellent catalytic activity in CO oxidation reactions. We demonstrate that the temperature-controlled decomposition of [Cu(NH3)4](MnO4)2 in CHCl3 and CCl4 at 61 and 77 °C, respectively, gives rise to the formation of amorphous CMO and NH4NO3, which greatly influences the composition as well as the Cu valence state of the annealed CMOs. Washing with water and annealing at 300 °C result in a BAC-CMO material, whereas the direct annealing of the as-prepared product at 300 °C gives rise to crystalline CuMn2O4 (sCMO, 15-40 nm) and ((Cu,Mn)2O3, bCMO, 35-40 nm) mixture. The annealing temperature influences both the quantity and crystallite size of sCMO and bCMO products. In 0.5% CO/0.5% O2/He mixture the best CO to CO2 conversion rates were achieved at 200 °C with the BAC-CMO sample (0.011 mol CO2/(m2 h)) prepared in CCl4. The activity of this BAC-CMO at 125 °C decreases to half of its original value within 3 h and this activity is almost unchanged during another 20 h. The BAC-CMO catalyst can be regenerated without any loss in its catalytic activity, which provides the possibility for its long-term industrial application.

Evaluation of Co/SSZ-13 Zeolite Catalysts Prepared by Solid-Phase Reaction for NO-SCR by Methane.

Co/SSZ-13 zeolites were prepared by heating the finely dispersed mixture of NH4-SSZ-13 and different cobalt salts up to 550 °C. Investigations by thermogravimetry - differential scanning calorimetry - mass spectrometry provided new insight into details of the solid-state reaction. Formation of Co carrying hydrate melt or volatile species was shown to proceed from chloride, nitrate, or acetylacetonate Co precursor salts upon thermal treatment. This phase change allows the transport of the Co species into the zeolite pores. The reaction of the NH4+ or H+ zeolite cations and the mobile Co precursors generates vapor or gas products, readily leaving the zeolite pores, and cobalt ions in lattice positions suggesting that solid-state ion-exchange is the prevailing process. The obtained catalysts are of good activity and N2 selectivity in the CH4/NO-SCR reaction. The thermal treatment of acetate or formate salts give solid intermediates that are unable to get in contact and react with the cations in the zeolite micropores. These catalysts contain mainly Co-oxide clusters located on the outer surface of the zeolite crystallites and have poor catalytic performance.