Wilson D. Shafer

Hydrocracking and Hydroisomerization of n-Hexadecane, n-Octacosane and Fischer–Tropsch Wax Over a Pt/SiO2–Al2O3 Catalyst

The hydroisomerization and hydrocracking of long chain n-paraffins and a Fischer–Tropsch wax produced with a cobalt catalyst were accomplished over a Pt–amorphous silica–alumina catalyst. The relative conversion of the n-hexadecane and n-octacosane mixed feed greatly favored the higher carbon number compound even though the conversions of the pure hydrocarbons were the same within a factor of two or less when converted separately. Thus, vapor equilibrium plays a role for the conversion of the heavier alkanes and in this case the conversion essentially occurs with only the compound present in the liquid phase. The single branched cracked products show a peak at the mid-carbon number, C8 and C14 for the two reactants, but the peak for the multi-branched product occurs at a higher carbon number. Thus, it appears that the multi-branched products are primarily produced in a series reaction with the singly branched compounds being formed as the primary products. The data for wax conversion are consistent with the competitive conversion operating for the higher carbon number compounds; however, the transport of intermediate carbon number products from the reactor occurs more rapidly than their formation rates by cracking reactions. The data clearly show that the hydrocracking of wax is dominated by vapor–liquid equilibrium and that hydrocracking is initially controlled by the compounds present in the liquid phase.Graphical AbstractFigure shows the catalyst pore filling with low boiling (left) and high boiling (right) hydrocarbons. Each reactant saturates the catalytic sites and the breaking of C–C bond occurs. Once the products from cracking of the liquid phase go into the vapor phase, it should rapidly pass the catalyst bed. This short contact time on gas phase hydrocarbons relative to the liquid phase, limits the conversion of low boiling point hydrocarbons.

Fischer–Tropsch Synthesis: Effect of Potassium on Activity and Selectivity for Oxide and Carbide Fe Catalysts

The effect of potassium on oxides and carbides of iron for Fischer–Tropsch synthesis (FTS) was investigated by pretreating Fe3O4 and K-promoted Fe catalysts with different gases (H2/H2O and CO). A freshly activated sample and catalysts that were recovered from the CSTR before, during and after FT synthesis were characterized ex situ using Mössbauer spectroscopy. Iron carbide is found to be active for both FT and water gas shift (WGS) reactions. After H2/H2O activation, all three catalysts (Fe3O4, low α-Fe, and high α-Fe) exhibit a steady but low FT activity for a period of FT synthesis. However, both FT and WGS activity for Fe3O4 and low α-Fe catalysts were greatly improved after CO activation. In contrast, the high potassium containing catalyst (high α-Fe) did not show any further improvement in activity after CO activation. The difference in FT and WGS activity observed after pretreatment conditions using these catalysts may be associated to the amount of potassium and conversely the iron carbide present in the catalysts.Graphical Abstract

Fischer–Tropsch synthesis: effect of ammonia on product selectivities for a Pt promoted Co/alumina catalyst

The effects of co-fed ammonia in synthesis gas on the activity and product selectivities of a typical cobalt catalyst (0.5% Pt–25% Co/Al2O3) were investigated during the Fischer–Tropsch synthesis using a continuously stirred tank reactor (CSTR). The product selectivities were compared at a similar CO conversion level for various concentrations (10–1000 ppmv) of ammonia, as well as clean (un-poisoned) conditions. The addition of 10–1000 ppmv ammonia (concentration of ammonia with respect to the syngas feed) significantly decreased activity; the percentage of deactivation was similar (∼40%) for the various concentrations of ammonia used. At similar CO conversions, the addition of ammonia caused an increase in olefin selectivity and the corresponding paraffin and alcohol selectivities were decreased compared to the ammonia free synthesis conditions. Olefin selectivity increased with increasing concentration of ammonia, and the paraffin and alcohol selectivities were decreased with increasing ammonia concentration. At similar CO conversions, ammonia addition exhibited a positive effect on hydrocarbon selectivity (i.e., lower light gas products and higher C5+) and also light gas product selectivities (C1–C4) were decreased and C5+ selectivity increased with increasing concentration of ammonia compared to ammonia free conditions.

Hydrogenation of carbon dioxide over K-Promoted FeCo bimetallic catalysts prepared from mixed metal oxalates

The hydrogenation of carbon dioxide over K‐promoted FeCo bimetallic catalysts prepared by sequential oxalate decomposition and carburization of FeCo with CO was studied in a fixed‐bed reactor at 240 °C and 1.2 MPa. The initial CO2 conversion was found to be dependent on K loading, whereas both unpromoted and K‐promoted FeCo catalysts (except 90Fe10Co3.0K) exhibited similar levels of CO2 conversion after a few hours of time on stream. A decarburization study on freshly activated and used FeCo suggests that potassium increases the stability of iron carbides and graphitic carbon under a reducing atmosphere. Also, K addition tends to decrease the hydrogenation function of FeCo bimetallic catalysts and, thus, controls product selectivity. Under similar CO2 conversions, potassium enhanced acetic acid formation while suppressing ethanol production, which indicates that a common intermediate might be responsible for the changes observed with C2 oxygenates.

Deuterium Exchange Study for Hydrogenation of D5-1-Pentene (4,4,5,5,5) Over Conventional Cobalt Fischer–Tropsch Catalyst

The hydrogen–deuterium exchange reaction was performed for hydrogenation of D5-1-pentene (4,4,5,5,5) under realistic cobalt Fischer–Tropsch synthesis conditions. In the presence of CO, the added deutero-1-pentene did not show any significant H/D exchange but a step-wise H/D exchange occurs when CO was replaced with N2. The inhibition effects of CO and other FT products on H/D exchange of D5-1-pentene and a pressure dependency effect on H/D exchange are observed.Graphical Abstract

Dehydration of 1,5‐Pentanediol over Na‐Doped CeO2 Catalysts

The effects of CeO2 doped with Na on the dehydration of 1,5‐pentanediol were studied by using a fixed‐bed reactor at two different temperatures (350 and 400 °C) and atmospheric pressure. For characterization, BET surface area, hydrogen temperature‐programmed reduction, CO2 temperature‐programmed desorption, and diffuse reflectance infrared Fourier transform spectroscopy techniques were utilized. The conversion of the diol on CeO2 was found to depend on Na loading. The selectivity to the desired product (i.e., unsaturated alcohol) increased and the selectivity to undesired products (i.e., tetrahydropyran, tetrahydropyran‐2‐one, cyclopentanol and cylopentanone) decreased with increasing Na content on CeO2. The basicity of hydroxyl groups or surface oxygen on CeO2 was altered with the addition of Na, and controlled the dehydration reaction pathway.

Dehydration of 2-octanol over CeO2-CaO mixed oxides

Vapor‐phase catalytic dehydration of 2‐octanol was investigated over Ca‐doped CeO2 at 375 °C and atmospheric pressure. Ca doping up to 0.15 wt % was found to increase the dehydration activity for 2‐octanol, whereas further increases in Ca content (0.50 and 1.25 wt %) detrimentally affected the conversion. Catalyst surface area and pore volume increased with increasing Ca content in Ca‐doped CeO2. Hydrogen temperature‐programmed reduction (TPR) profiles indicate that the partially reduced state of surface ceria (i.e., Ce3+), which increases with increasing Ca loading up to 0.15 wt %, might play an important role in promoting dehydration.

Fischer–Tropsch synthesis: effect of Cu, Mn and Zn addition on activity and product selectivity of cobalt ferrite

The effect of Cu, Mn and Zn addition on cobalt ferrite was investigated for Fischer–Tropsch synthesis (FTS). Oxalate co-precipitation followed by decomposition under inert conditions was used to obtain various metal containing cobalt ferrites (Co0.7M0.3Fe2O4). The carburization of cobalt ferrite in flowing CO at 270 °C and 175 psig yielded iron carbides (χ-Fe5C2 and e′-Fe2.2C) along with a bimetallic FeCo alloy. The extent of carburization was compared among Cu, Mn, and Zn doped catalysts with undoped cobalt ferrites under similar conditions. XRD and Mossbauer spectroscopy analysis of the freshly carburized samples followed by passivation revealed that carburization of cobalt ferrite did not change appreciably with addition of Cu or Mn. On the other hand, Zn was found to retard the carburization of cobalt ferrite. Analysis of the used FT catalysts suggests that Cu is less efficient over Mn and Zn in stabilizing the iron carbides (i.e., active form of iron) during FT synthesis. The FT activity remains more or less the same for the undoped, Cu and Zn containing cobalt ferrites at higher temperatures. The CO conversion of Co0.7Mn0.3Fe2.0 catalyst was much lower than the other catalysts tested. Addition of Zn or Mn to cobalt ferrite was found to promote alcohol formation, particularly at higher reaction temperatures. The water–gas shift activity of the catalysts was found to decrease in the following order, Co1.0Fe2.0 > Co0.7Mn0.3Fe2.0 > Co0.7Zn0.3Fe2.0 > Co0.7Cu0.3Fe2.0.

Fischer–Tropsch Synthesis: XANES Spectra of Potassium in Promoted Precipitated Iron Catalysts as a Function of Time On-stream

XANES K-edge spectra of potassium promoter in precipitated Fe catalysts were acquired following activation by carburization in CO and as a function of time on-stream during the course of a Fischer–Tropsch synthesis run for a 100Fe:2K catalyst by withdrawing catalysts, sealed in wax product, for analysis. CO-activated and end-of-run spectra of the catalyst were also obtained for a 100Fe:5K catalyst. Peaks representing electronic transitions and multiple scattering were observed and resembled reference spectra for potassium carbonate or potassium formate. The shift in the multiple scattering peak to higher energy was consistent with sintering of potassium promoter during the course of the reaction test. The catalyst, however, retained its carbidic state, as demonstrated by XANES and EXAFS spectra at the iron K-edge, suggesting that sintering of potassium did not adversely affect the carburization rate, which is important for preventing iron carbides from oxidizing. The method serves a starting point for developing better understanding of the chemical state and changes in structure occurring with alkali promoter.Graphical Abstract