Robert A. Keogh

Sulfated zirconia as a hydrocarbon conversion catalyst

Abstract Platinum containing sulfated zirconia is a more active catalyst for hydrocarbon isomerization and cracking than most, if not all, zeolite cracking catalysts. A survey of the literature data suggests that the preparation technique, initial calcination and final catalyst treatment play important roles in determining catalyst activity. The final treatment probably is the most important and least controlled step in most studies to date. Whether the catalytic site involves Lewis or Bronsted acidity is debated; our data indicate Bronsted acidity as more likely. The role of a supported metal, e.g., Pt, is to provide a hydrogenation role but many attribute a second role for it in generating acidity through hydrogen spillover. For hexadecane conversions, increasing the hydrogen pressure increases the cracking to lower molecular weight hydrocarbons. The presence of small amounts of hydrogen donors are claimed to improve isomerization selectivity.

Fischer–Tropsch synthesis. Effect of CO pretreatment on a ruthenium promoted Co/TiO2

The effect of pretreatment, using hydrogen or carbon monoxide, on the activity and selectivity of a ruthenium promoted cobalt catalyst (Ru(0.20 wt%)/Co(10 wt%)/TiO2) during Fischer–Tropsch (FT) synthesis was studied in a continuous-stirred tank reactor (CSTR). The hydrogen reduced catalyst exhibited a high initial synthesis gas conversion (72.5%) and reached steady state after 40 h on stream, after which the catalyst deactivated slightly with time on stream. The carbon monoxide reduced catalyst reached steady state quickly and showed a lower activity and a good stability. Methane selectivity on the carbon monoxide reduced catalyst was 15–20% (carbon base), much higher than that on the hydrogen reduced catalyst (5–10%). Carbon monoxide regeneration increased the activity on the hydrogen reduced catalyst; however, it did not have significant effect on the carbon monoxide reduced catalyst.

PtSO42−ZrO2 catalysts. Correlation of catalytic activity with SO42− XPS data

Increasing activity for the conversion of n-hexadecane is observed for 0.6% PtSO42−ZrO2 catalysts with increasing time of activation in air at 500°C (773 K). XPS analysis suggests that, rather than a change in the crystal phase, this increase is due to a loss of water and/or an increase in surface concentration of SO42−. It is noted that there is a reasonably good correlation between the relative surface sulfate concentration and relative conversion of n-hexadecane with increasing heating time, although there are minor differences. In spite of the many assumptions that were made to generate the two curves showing the relative XPS peak area and the catalytic activity, there is surprising agreement between the two. It is therefore inviting to relate the catalytic activity for n-hexadecane conversion to that of the sulfate group. Furthermore, it appears that the active site related to the sulfate group is not one that contains water in its make-up.

XPS investigation of an iron/manganese/sulfated zirconia catalyst

Abstract A sample of Fe–Mn–SO 4 2− –ZrO 2 has been heated at 500°C in air for 98 h. At intervals, the sample was evacuated and transferred without atmospheric exposure to an XPS chamber. As noted with Pt–SO 4 2− –ZrO 2 , the O 1s peak resolved to a doublet; one of these peaks is interpreted to result by dehydration of the sulfate group. Following the 98 h air treatment, the sample was treated at 150°C at 1 atm in flowing hydrogen for a total of 78 h. The XPS spectra, obtained at intervals during the heating in hydrogen, showed that both Fe and Mn remained in an oxidized state.

Thermal and catalytic conversion of asphaltenes

Abstract Asphaltenes isolated from coal liquids and tar sand bitumen have been converted thermally and with acid and/or hydrogenation catalysts. The conversions, based on solubility classes — preasphaltenes, asphaltenes and oil — have been determined for increasing reaction time. The removal of heteroatoms in each solubility class was also followed with increasing conversion. Gaseous deuterium was utilized in some studies to follow the extent of exchange reactions. There is a rapid initial conversion at each reaction temperature, and this is followed by a much slower conversion process. The deuterium distribution in the products suggest that the asphaltene decomposes to produce a stable oil molecule and a radical fragment that remains in the asphaltene solubility range.

Sulfated zirconia catalysts: Are Bronsted acid sites the source of the activity?

The thermal decomposition products of pyridinium sulfate differ from those of pyridinium sulfate supported on zirconia which in turn differs from that of pyridine adsorbed on a sulfated zirconia. Unsupported pyridinium sulfate decomposes to produce pyridine and sulfuric acid, and these subsequently react to produce oxides of carbon and sulfur. Zirconia that is sulfated and then exposed to pyridine does not release detectable amount of pyridine during heating in an inert gas; rather the pyridine undergoes oxidation reduction reactions simultaneously to release CO2 and sulfur compounds. Pyridinium sulfate supported on zirconia decomposes upon heating to release pyridine and sulfuric acid, which reacts with the zirconia. The desorption of pyridine in one case and only CO2/SOx in the other case suggests that sulfated zirconia does not contain Brønsted acidity that can form pyridinium sulfate.

The effect of Pt concentration on the activity and selectivity of SO42−ZrO2 catalysts for the hydrocracking and hydroisomerization of n-hexadecane

Abstract The addition of Pt to promote the long-term activity of SO 4 2− ZrO 2 catalysts is showm to have a strong influence on the conversion of n-hexadecane. The maximum conversion occurs at the 0.6–1.0 wt.% Pt concentration range; increasing further the Pt concentration up to 5.0 wt.% does not increase the conversion of n-hexadecane. At a constant conversion, the selectivity for isomerization and cracking is the same for different levels of Pt. However, the carbon number distribution of the cracked products shows a small shift to higher carbon numbers with increasing Pt loadings.

Activation and characterization of FeMnSO42−ZrO2 catalysts

Abstract Changes in FeMnSO 4 2− ZrO 2 catalyst formulations during activation have been observed. In air or an inert gas, the added salt, such as iron and/or manganese nitrate, decomposes over a temperature range of about 200–400°C to produce nitric oxide, oxygen and iron and/or manganese oxide. The crystallization of zirconia occurs at 450°C; when the sample contains sulfate the exothermic event occurs at a temperature that is about 200°C higher. Heating in the presence of hydrogen causes the evolution of nitric oxide to occur over a narrow temperature range and at a lower temperature than when the sample is heated in helium or air. It appears that the nitrate ions associated with Fe, Mn and Zr decompose to produce nitric oxide, and presumably water, at different temperatures when the sample is heated in the presence of hydrogen. Heating samples of sulfated zirconia containing iron and/or manganese in hydrogen causes sulfur evolution at a lower temperature, and a significant fraction of it in the form of H2S.

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.

Hydroconversion of n-hexadecane with Pt-promoted monoclinic and/or tetragonal sulfated zirconia catalysts

A series of mixed Pt-promoted monoclinic and tetragonal sulfated zirconia catalysts were prepared and characterized. The catalysts contained 27–86% of the monoclinic phase. The zirconia samples were prepared by varying the speed of precipitation of the hydrous zirconia and the pH of the final solution. The hydrous zirconia was then calcined prior to promotion with Pt and sulfate. The catalysts were activated just prior to activity studies with n-hexadecane. This synthesis route and pretreatment produced mixed-phase catalysts which yielded comparable conversion and selectivity data to that of a purely tetragonal catalyst using optimum conditions. The data show that an active catalyst can be obtained with the monoclinic phase present and that addition of sulfate after development of the crystalline phases can yield an active catalyst.