N.B. Jackson

Attrition of precipitated iron Fischer-Tropsch catalysts

Abstract A precipitated, doubly promoted, iron oxide catalyst was studied to elucidate phenomena that may lead to catalyst attrition during slurry phase Fischer-Tropsch synthesis. The catalyst was examined by electron microscopy (SEM and TEM), electron and X-ray diffraction, sedigraph particle size analysis and BET surface area measurements. The catalyst undergoes attrition both at the micro- as well as the nano-length scales. On the micro-scale, this involves a breakup of ca. 30 μm spherical agglomerates into ca. 1 μm particles, a process that can be initiated even by the mixing that occurs in the sedigraph analyzer. On the nano-scale, we find that exposure of the catalyst to CO at increasing temperatures transforms single crystals of α-Fe 2 O 3 into Fe 3 O 4 and ultimately to Fe-carbide, with rounded particles as small as ca. 20 nm. The details of phase transformations and the resulting crystallite morphology and size distribution could play a major role in influencing the overall attrition resistance of precipitated iron oxide catalysts. In this paper, we describe the effects of the CO activation temperature on catalyst structure at the micro- and nano-scales.

The formation of active species for oxidative dehydrogenation of propane on magnesium molybdates

Pure and mixed magnesium molybdate phases (MoO3, MgMoO4, and MgMo2O7) have been examined for the oxidative dehydrogenation reaction of propane. The results are very sensitive to the stoichiometry and method of preparation. The catalysts exhibiting superior activity and selectivity are characterized by a unique temperature-programmed reduction peak that is not present for the poorly active or selective catalysts. Mixtures of MgMoO4 and MoO3 or MgMoO4 and MgMo2O7, materials that perform poorly by themselves, show significant improvements in performance upon heating. The solid-state interactions leading to these improvements correspond to the appearance of the characteristic reduction peak. The results suggest that the beneficial synergistic effects seen with mixtures of inactive phases are due to formation of a new phase or species, rather than remote communication between phases (e.g., oxygen spillover).

Oxidation Reactions of Ethane over Ba-Ce-O Based Perovskites

Abstract Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeO 3 perovskites under oxygen limited conditions. Several of the materials, notably the Ca- and Y-substituted materials, show activity for complete oxidation of the hydrocarbon to CO 2 at temperatures below 650°C. At higher temperatures, the oxidative dehydrogenation (ODH) to ethylene becomes significant. Conversions and ethylene yields are enhanced by the perovskites above the thermal reaction in our system in some cases. The perovskite structure is not retained in the high temperature reaction environment. Rather, a mixture of carbonates and oxides is formed. Loss of the perovskite structure correlates with a loss of activity and selectivity to ethylene.

Deactivation and attrition of iron catalysts in synthesis gas

A number of different iron Fischer-Tropsch catalysts were characterized with an emphasis on the study of morphological changes of the iron and iron carbide, phases as well as the growth and morphology of carbon species during reaction. The effects of catalyst composition, reaction temperature, and pretreatment were investigated. Temperature programmed surface reaction of H 2 with a number of used catalysts revealed the formation of more than one carbide under certain circumstances. This paper considers deactivation and catalyst attrition for catalysts reacted in a slurry phase autoclave reactor. Several similar catalysts were tested for activity for long periods of time (1000–3000 h), and it was found that when operated properly, these iron Fischer-Tropsch catalysts can be run in slurry reactors with only modest deactivation, during the time periods tested.

Diplomacy for science: strategies to promote international collaboration

Technology innovation is an increasingly globalized exercise with dramatic consequences for scientific and diplomatic goals alike, and requires enhanced participation and integration of scientists and science-minded diplomats within diplomatic missions to advance shared policy goals. This more general problem is addressed in the present article by focusing on recent collaborations between U.S. and German scientists, including several of the coauthors.

Attrition-determining morphology changes on iron Fischer-Tropsch catalysts

Temperature programmed reduction and transmission electron microscopy were used to study the morphology changes of an iron Fischer-Tropsch catalyst during reaction, with an emphasis on potential attrition of the catalyst. In particular, the effect of potassium promotion was explored. Potassium appeared to minimize the formation of one type of carbide and, at low concentrations, limited graphitic carbon formation. At higher potassium levels (3%) graphitic carbon began to re-appear. Copper-promoted catalysts exposed to higher reaction temperatures (which is known to cause attrition) formed different carbides than those exposed to lower reaction temperatures. The potassium promoted catalysts investigated in this study did not produce the high temperature carbide present on catalysts that quickly attritted.

Zirconium-Titanium Phosphate Acid Catalysts Synthesized by Sol Gel Techniques

Recently a large effort has been put into identifying solid acid materials, particularly sulfated zirconia and other sulfated metal oxides, that can be used to replace environmentally hazardous liquid acids in industrial processes. The authors are studying a group of mixed metal phosphates, some of which have also been sulfated, for their catalytic and morphological characteristics. Zirconium and titanium are the metals used in this study and the catalysts are synthesized from alkoxide starting materials with H{sub 3}PO{sub 4}, H{sub 2}O, and sometimes H{sub 2}SO{sub 4} as gelling agents. The measurement of acidity was achieved by using the isomerization of 2-methyl-2-pentene as a model reaction. The phosphate stabilized the mixed metal sulfates, preventing them from calcining to oxides boosting their initial catalytic activity. The addition of sulfate prevented the formation of the catalytically inactive mixed metal pyrophosphates when calcined at high temperatures (> 773 K).

Catalyst technology roadmap report

This report outlines the future technology needs of the Chemical Industry in the area of catalysis and is a continuation of the process that produced the report Technology Vision 2020: The U.S. Chemical Industry and the Council for Chemical Researchs (CCR) Chemical Synthesis Team follow-up work in chemical synthesis. Vision 2020 developed a 25-year vision for the chemical industry and outlined the challenges to be addressed in order to achieve this vision. This report, which outlines the catalysis technology roadmap, is based on the output of the CCRs Chemical Synthesis Team, plus a workshop held March 20-21, 1997, which included about 50 participants, with catalysis experts from industry, academia, and government. It is clear that all participants view catalysis as a fundamental driver to the economic and environmental viability of the chemical industry. Advances in catalytic science and technology are among the most crucial challenges to achieving the goals of the chemical industry advanced in Vision 2020. CATALYST TECHNOLOGY ROADMAP

Carbide formation during activation of iron Fisher-Tropsch catalysts

The morphological transformations during activation of a commercial, precipitated and spray-dried, Fe2O3-CuO-K2O Fischer-Tropsch Catal.yst are studied. The Catal.yst is activated in a flowing (H2/CO = 0.7/1.0) mixture at 523 K and 543 K and subsequent reaction is carried out at 523 K. The activation temperature causes these Catal.ysts to exhibit significant differences in their Catal.ytic activity for CO hydrogenation. The solid-state phase transformations from the oxide phase (hematite) to the iron carbide are studied by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and elemental analysis. The differing extents of formation of the carbide phase correlate well with the Catal.ytic activity of iron. HRTEM shows that as magnetite transforms into carbide, the crystals of magnetite break down into smaller crystallites of the carbide phase. Deposition of carbon on the surface causes the carbide crystallites to further separate from each other. Morphological transformations such as these determine the attrition of the Catal.yst and help provide clues to understanding the deactivation of iron Fischer-Tropsch Catalysts.

Structure-property relationships of BaCeO perovskites for the oxidative dehydrogenation of alkanes

The oxidative dehydrogenation (ODH) reactions for the formation of two important organic feedstocks ethylene and propylene are of great interest because of the potential in capital and energy savings associated with these reactions. Theoretically, ODH can achieve high conversions of the starting materials (ethane and propane) at lower temperatures than conventional dehydrogenation reactions. The important focus in this study of ODH catalysts is the development of a structure-property relationship for catalyst with respect to selectivity, so as to avoid the more thermodynamically favorable combustion reaction. Catalysts for the ODH reaction generally consist of mixed metal oxides. Since for the most selective catalyst lattice oxygen is known to participate in the reaction, catalysts are sought with surface oxygen atoms that are labile enough to perform dehydrogenation, but not so plentiful or weakly bound as to promote complete combustion. Also, catalysts must be able to replenish surface oxygen by transport from the bulk. Perovskite materials are candidates to fulfill these requirements. The authors are studying BaCeO{sub 3} perovskites doped with elements such as Ca, Mg, and Sr. During the ODH of the alkanes at high temperatures, the perovskite structure is not retained and a mixture of carbonates and oxides is formed, as revealed by XRD. While the Ca doped materials showed enhanced total combustion activity below 600 C, they only showed enhanced alkene production at 700 C. Bulk structural and surface changes, as monitored by powder X-ray diffraction, and X-ray photoelectron spectroscopy are being correlated with activity in order to understand the factors affecting catalyst performance, and to modify catalyst formulations to improve conversion and selectivity.