Search

The influences of nitric acid treatment on a carbon nanotube (CNT) support and the preparation method, incipient wetness impregnation (IWI) versus chemical vapor deposition (CVD), on catalytic performance during Fischer–Tropsch (FT) synthesis were examined using a slurry phase reactor. Acid treated CNT (ACNT) supported Ru catalysts exhibited higher activities compared to Ru supported on untreated CNTs (UCNTs). The acid-treated CVD catalyst had higher initial CO conversion (smaller average Ru particle size) but sintered more due to a greater tendency for Ru to be deposited exterior to CNT channels relative to IWI. After the initial decline and leveling off period, the ACNT IWI catalyst had the highest steady activity among the catalysts tested. The ACNT IWI catalyst also displayed greater oxygenate selectivity (∼17%) compared to ACNT CVD (∼12%) and UCNT IWI (∼10%) catalysts at similar conversions. Acid treatment created adsorption sites on the CNT surface that anchor Ru precursors and promote CO insertion ...

A series of Co–Fe bimetallic catalysts was prepared, characterized, and studied for the hydrogenation of carbon dioxide. The catalyst precursors were prepared via an oxalate coprecipitation method. Monometallic (Co or Fe) and bimetallic (Co–Fe) oxalate precursors were decomposed under a N2 flow at 400 °C and further pretreated under a CO flow at 250 °C. The catalysts (before decomposition of the oxalates or after activation) were characterized by BET, TGA-MS, X-ray diffraction, CO-TPR, SEM, HR-TEM, and Mossbauer spectroscopy techniques. The hydrogenation reaction of CO2 was performed using Co–Fe bimetallic catalysts pretreated in situ in a fixed-bed catalytic microreactor operating in the temperature range of 200–270 °C and a pressure of 0.92 MPa. With increasing Fe fraction, the selectivity to C2–C4 for Co–Fe catalyst increased under all operating conditions. The alcohol selectivity was found to increase with increasing iron content of the Co–Fe catalyst up to 50%, but then it dropped with further additi...

Tracer studies were performed on cobalt and iron Fischer–Tropsch catalysts using a synthesis gas containing a 20:80 mixture of 13C18O and 12C16O. The objective of the work was to investigate the antecedents of the C–O bonds in alcohols and CO2 formed during Fischer–Tropsch (FT) synthesis. It was found that chain growth proceeded by a CO insertion mechanism over both cobalt and iron catalysts. Over the cobalt catalyst, the dominant pathway for methanol synthesis involved a partial hydrogenation of CO as well as CO2 by a reaction pathway separate from the Fischer–Tropsch pathway. Over the iron catalyst, the majority of the methanol was formed by partial hydrogenation of only CO through the FT reaction pathway. Iron is active for water gas shift conversion, which produced CO2. Oxygen exchange reactions of CO2 were likely over both catalysts and complicated the interpretation of the results.

The current investigation was undertaken to identify limits of hydrohalic acid (HX, X = F, Cl, Br) impurities in syngas and shed light on the mechanism of HX poisoning of a 100 Fe/5.1 Si/2 Cu/3 K FTS catalyst under industrially relevant conditions using a 1-L slurry-phase reactor. Co-feeding

The conversion of CO2 over a CoPt/Al2O3 catalyst was investigated. Single-gas adsorption studies indicated that carbon was deposited on the catalyst by exposure to both CO2 and CO in the absence of H2 cofeed. When CO2 was preadsorbed followed by H2 flow, methane was produced, as well as traces of C3–C4 hydrocarbons, but no evidence of the reverse water gas shift reaction was found. Use was made of carbon-14-labeled carbon dioxide to track CO2 conversion and selectivity during reaction of syngas mixtures with different ratios of CO, CO2, and H2. Absence of 14C in unconverted CO and the unequal molar concentration of 14C in the products from reaction at 220 °C and 2 MPa provided strong evidence that 14CO2 was not converted by the reverse water gas shift reaction. The antecedence of the carbon from CO2 mattered, and the carbon did not become part of a common carbon pool for hydrocarbon synthesis. Conversion of CO2 proceeded by a pathway separate from CO. Conclusions drawn from this experimental study were em...

The performance of carbon-supported cobalt catalysts was compared with that of Co/γ-Al2O3 reference catalysts for the Fischer–Tropsch synthesis (FTS) reaction. The carbon support (CS) was prepared using a hydrothermal method that formed mostly spherical ∼300–800 nm carbons that were first carbonized at 900 °C and then partially graphitized at 1900 °C. The FTS study was conducted using a continuously stirred tank reactor, and the cobalt catalysts were promoted with Pt (0.2% Pt–10% Co) to facilitate the reduction of cobalt oxides. Catalysts were prepared by an evaporative method (Co/CS-IWI) and by a chemical vapor deposition technique (Co/CS-CVD). The CVD technique led to a higher CO conversion (26.5%) relative to the conventional evaporative (IWI) method (7.4%) at the same temperature (220 °C) and space velocity (1.5 NL/gcath). Remarkably, the Co/CS-CVD displayed a high oxygenate selectivity (∼10%) in comparison with cobalt alumina catalysts (i.e., including one having similar Pt and Co loadings, as well a...

To define the mechanism of the Fischer–Tropsch synthesis, numerous experiments probed the rate-determining step by performing isotopic experiments during CO hydrogenation. The aim of this work was to determine if there is an isotopic effect for adsorption for either hydrogen or deuterium on the cobalt metal surface of a Fischer–Tropsch synthesis catalyst. If a partitioning effect is noticed, there is a possibility for this to interfere with measurements of the inverse kinetic isotopic effect during CO hydrogenation. In this investigation, the partitioning of hydrogen and deuterium on an activated cobalt catalyst was examined using temperature programmed desorption and gas chromatography. The results indicate that there may be hydrogen–deuterium exchange with the support, but there is no significant isotopic partitioning on the cobalt metal surface.