Slurry Phase Iron Catalysts for Indirect Coal Liquefaction

This report describes research conducted to support the DOE program in indirect coal liquefaction. Specifically, we have studied the attrition behavior of Iron Fischer-Tropsch catalysts, their interaction with the silica binder and the evolution of iron phases in a synthesis gas conversion process. The results provide significant insight into factors that should be considered in the design of catalysts for the conversion of coal-derived synthesis gas into liquid fuels

SLURRY PHASE IRON CATALYSTS FOR INDIRECT COAL LIQUEFACTION Semi-Annual Technical Report

Abstract This report describes research conducted to support the DOE program in indirect coal liquefaction. Specifically, we have studied the attrition behavior of iron Fischer-Tropsch catalysts, their interaction with the silica binder and the evolution of iron phases in a synthesis gas conversion process. The results provide signficant insight into factors that should be considered in the design of catalysts for converting coal based syn-gas into liquid fuels. Executive Summary This report covers the third six months of this three year grant under the University Coal Research program. During this period, we have explored the uniaxial compaction method as an approach to derive particle breaking stress. The method was applied to alumina support granules obtained from Dr. Robert Gormley at PETC and will be extended to other F-T catalysts in future work. We also present ultrasonic fragmentation analysis of Fe/alumina F-T samples obtained from PETC. When the particle size evolution is compared with that of the base UCI catalyst, it is clear that the alumina-supported catalysts show significant improvement in particle strength. This work will be continued over the next six month period to better quantify the agglomerate strength of F-T catalysts, and to afford comparisons between the uniaxial compaction and ultrasonic fragmentation methods for determining the strength of F-T catalysts. During this period, we have continued our study of Fe/silica interactions to provide a fundamental understanding of the how silica binders influence the activity and attrition resistance of these catalysts. To understand differences in the reducibility of the iron phase caused by silica, we have set up a temperature programmed reduction facility. TPR in H 2 as well as in CO was performed of Fe/SiO 2 catalysts prepared by impregnation as well as by precipitation. We have completed analysis of catalysts received from slurry reactor runs at Texas A&M university (TAMU) and the University of Kentucky Center for Applied Energy Research (CAER) by x-ray diffraction. The analysis results were conveyed to PETC, TAMU and CAER in September 96 are included here for the sake of completeness. The purpose of the XRD analysis was to determine the phase composition of catalysts derived from a slurry reaction run using Fe Fischer-Tropsch catalysts. As we describe in this report, the XRD results show that the carbide phase does not transform into magnetite over the course of a F-T run, both in the TAMU as well as in the CAER runs. The slow deactivation of these catalysts must then be related to crystallite growth and loss of active phase surface area. Further work is underway to corroborate this hypothesis. Technical Objectives The objective of this research project is to perform fundamental research in support of catalyst development for slurry phase bubble column reactors for Fischer-Tropsch synthesis. The overall program is divided into the following tasks: Task 1. Catalyst Particulate Synthesis Task 2. Catalyst Binder Interactions. In task 1, we will first study factors that determine the attrition resistance of slurry phase Fe catalysts. Fundamental understanding of the attrition phenomenon will be used to guide the synthesis of novel precipitated catalysts that overcome some of the limitations of current generation catalysts. The investigation of catalyst microstructure as a function of treatment will help determine the optimal treatment protocols for F-T synthesis catalysts. Since the use of binders is considered essential for providing the desired attrition resistance, the second 3 task is to perform fundamental studies of catalyst-binder interactions. These studies will use model catalysts that can be studied by high resolution transmission microscopy to investigate the nature of interfacial phases at the Fe-binder interface. A better understanding of the phenomena that lead to catalyst-binder interactions will help us design improved catalysts for indirect coal liquefaction. Task 3. Characterization of catalysts received from CAER, Univ. of Kentucky, and from Texas A&M. Task 3 was not included in our original proposal. However, we are pursuing these studies to help understand catalyst deactivation under actual reaction conditions. Technical Progress Task 1: Catalyst Particulate Synthesis Overview In the previous six-monthly report we showed how ultrasonic excitation followed by sedigraph particle size distribution can yield a simple test for the strength of catalyst agglomerates. While the breakdown of particles subjected to ultrasound energy provides a graphic measure of particle strength, a number of assumptions must be made to derive a quantitative measure of particle strength. Hence, during the current six month period we have explored the use of a more conventional test for particle strength. Uniaxial Compression Testing Uniaxial compression testing is a technique for characterizing the strengths of powders and granular materials. Previously, the conventional method used for compression tests was the "Brazilian test", in which individual particles were crushed between two platens (1). The drawback to this method was in the variability of strength due to variations of individual particle sizes and shapes. Furthermore, individual particle fracture loads are small (equivalent to a few grams' weight) such that the accuracy of the data might not be high. A simple alternative method consisted of replacing the individual particle with a confined bed of similar particles, inferring some average individual particle strength parameter from the behavior of the whole bed under compression (1). This method is easily achieved using a piston in a cylinder, hence this method involves a uniaxial compaction (as shown on the next page). P h Confined Uniaxial Compression Test Uniaxial compression testing has been used by a group at Sandia National Laboratories in the study of ceramic granule strength. The tests were performed at the Advanced Materials Laboratory (a joint Sandia National Labs-University of New Mexico facility located on the university research park). For comparison, uniformly sized glass spheres were also used in their study. Diametral compression strength tests, similar to the "Brazilian test", were performed (2) and the results were compared with those obtained with the uniaxial compaction test. The uniform-size glass spheres were used to eliminate the effects of shape and size factors, and minimize strength variability. Surprisingly, the results showed that the glass spheres also exhibited large variability in strength. The results for ceramic granules and uniform-size glass spheres were verified by using Weibull statistics; indeed, results the glass spheres gave similar Weibull parameters to those obtained from ceramic granules, indicating a large strength variability for individual glass spheres. Although the glass spheres were uniform in size, the large variability in strength was thought to arise from the large range in flaw sizes. To circumvent the tedious task of testing individual granules by the diametral compression test, pressure compaction (P-C) tests were also performed by Jill Glass and coworkers at SNL. Compaction behavior of these samples was determined by plotting the relative density of the compacted sample vs. the log of the compaction pressure as shown on the next page (2). 5 Relative Density Log(compaction pressure) Granule rearrangement Granule fracture + rearrangement Breakpoint This figure shows how the data of relative density vs log pressure can provide a semi-quantitative measure of agglomerate strength. As shown in this plot, compaction data tend to exhibit linear regimes that can be attributed to different compaction mechanisms (3). In the first regime, the gradual increase in relative density is due to particles, such as granules and agglomerates, sliding and rearranging without fracture. At this stage little compaction occurs, and only a small percentage of the void space is removed during rearrangement. It is often observed experimentally that this regime has a slope of ≈ 0.003-0.005. In the second regime, a sharp increase in relative density is due to deformation and fracture in conjunction with the sliding and rearrangement of particles (slope ≈ 0.2). At this stage a larger percentage of void space is removed during rearrangement. Best fit lines are often drawn through the points in the two linear regimes of the compaction plot. The intersection of these lines is called the breakpoint, which acts as a transition point for the two regimes. The breakpoint has been used as a semi-quantitative indicator of powder/granule strength or yield point, and is thought of as the average strength. Recent work at SNL, however, has demonstrated that it is more representative of the lower end of the range of powder or granule strengths. Beyond the second regime there may be another characteristic slope at higher pressures, but this has not been analyzed because it is still not well understood. In our work, we have explored the use of uniaxial compression testing to measure the strengths of Fischer-Tropsch catalysts. An Instron 5565 machine was used for compaction tests of these catalysts. This machine allows different-size dies to be used depending on the amount of samples available. We have chosen to work with an 1/8" die to minimize the amount of sample required for a given test. Experimental Details A sample of VISTA-B-965-500C (Alumina), obtained from Dr. Robert Gormley at the Pittsburgh Energy Technology Center (PETC), was used for the uniaxial compression testing. Ten milligrams of this sample were loaded into the cell of a die with a 1/8" opening. A plunger 6 was then placed on top of the filled die, taking great care not to compress the sample. To account for the error due to deformation of the top plunger and to the compliance of the crosshead, the displacement of the empty fixture as a function of load was subtracted from the displacement of the filled die. Compression tests were conducted by placing the filled die underneath the crosshead of the Instron machine. The crosshead was manually lowered such that it was just touching the top plunger. The displacement gauge was zeroed, and the crosshead was then activated at a rate of 1.00 mm/min. Testing was continued until a load of 1000 N was reached. The sample was repeated for reproducibility. For the first experiment, the sample was compacted at an aspect ratio, L f /D of 0.61 (where L f = final compact height and D = compact diameter); for the second experiment, the sample was compacted at an aspect ratio of 0.74. Results Figures 1 and 2 show plots of relative density vs. log of compaction pressure for the alumina. The relative density was calculated using the mass of alumina, initial compact height, measured displacement, and theoretical density. As expected, a low increase in relative density with an increase in pressure was followed by a region of sharp increase in relative density with pressure. The breakpoint was estimated by using best fit lines for the linear regimes and estimating the breakpoint via intersection of the lines. The breaking strength was determined to be 11.97 MPa from Ultrasonic fragmentation tests of F-T catalysts Figs. 3-5 provide fragmentation analysis of three of the catalysts also obtained from Dr. Robert Gormley at PETC. Future Work These results show that the uniaxial compaction and ultrasonic fragmentation tests may provide a good measure of the attrition resistance of F-T catalysts. Our future work will be devoted to developing consistent data analysis procedures for the compaction test and then comparing the ultrasonic fragmentation and compaction test results to the performance of catalysts in a slurry environment. We will expand the scope of these studies to include samples obtained from CAER and TAMU. During the course of this work, we will continue to study the microstructure of these catalysts to elucidate the role of binder morphology and loading on catalyst particle strength. Task 2 -Catalyst-binder interaction Overview The focus of the work performed during this period was temperature programmed reduction of supported and unsupported catalysts to study how the binder-catalyst interaction affects the reducibility of the iron phase. Experimental Two silica sphere supported iron catalysts, YJ/1-65A(20 wt % Fe, with 1 wt % Cu) and YJ/1-67(10 wt % Fe), were prepared by conventional incipient wetness impregnation and precipitation respectively. A UCI unsupported catalyst (1185-149, Fe 2 O 3 /CuO/K 2 O = 88.95/11/0.05) was used as a reference. In this study, a 10% CO/He or 10% H 2 /Ar reductant stream was used with 20-30 mg catalyst sample contained in a U-shaped quartz reactor. A Thermal Conductivity Detector (TCD) was used for the analysis. An in-line CO 2 trap or H 2 O trap located between the reactor and the detector was used to remove CO 2 or H 2 O formed during TPR process. The sample temperature was ramped in each experiment at 10 o C /min to 500 o C and then held at the latter temperature for 0.5-1 hour. Results Following an optimized TPR procedure, H 2 -TPR profiles were recorded for unsupported UCI-1185-149 catalyst where the effect of preconditioning, i.e. heating in flowing Ar at the specified temperature, was first explored (see CO-TPR Two sets of CO-TPR profile were also recorded for supported and unsupported catalysts ( Future Work We find that comparison of the 1st and 2nd run profiles of the unsupported catalyst shows 9 that the position of the peak corresponding to Fe 2 O 3 to Fe 3 O 4 is significantly changed for both H 2 as well as CO-TPR. This could be caused by severe sintering of the catalyst during the 1st-run TPR as well as phase segregation of copper from iron. While the promotion effect of copper on the reduction of iron catalysts has been seen in previous work, the effect of the copper on the formation of carbide phases is not well understood. In future work, we will examine the microstructure of catalysts removed at various stages of the TPR runs to help answer some of these questions, particularly the role of Cu and the nature of interaction of the iron oxide phase with the silica support. Task-3: Characterization of catalysts from Univ. of Kentucky & Texas A&M Overview The analysis of samples obtained from CAER and TAMU over the course of a continuous F-T run are presented below. XRD analysis of samples in wax from run SB-3425 performed at TAMU An XRD pattern of natural magnetite is enclosed for reference TOS=000 hrs TOS=111hrs TOS=233hrs TOS=330 hrs TOS=384hrs Summary Over the 400 hours of running in an FT synthesis reactor, there is no apparent transformation of the carbide into magnetite even though the CO conversion is 80%. The slight deactivation seen at 330 hours may be attributed to the increased peak height of the carbide peaks (in-10 creased crystallinity, loss of surface area) and could also be possibly related to the disappearance of the peak at 2.226 Å and 2.984 Å This may suggest transformation of one form of carbide into another. XRD analysis of samples in wax from run RJO-189 performed at CAER We have analyzed the catalyst samples from this run that are embedded in wax. Since, there is an overlap between carbide and magnetite peaks at around 2.1 Å, we have used Reitveld analysis to strip the magnetite peaks from the spectrum. In this way, the carbide peaks can be clearly identified and the phase transformations from carbide to magnetite better understood. RJO-189F TOS=20h RJO-189G TOS=122h RJO-189G TOS=122h RJO 189J TOS=888 h RJO 189M TOS=1796 h RJO 189M TOS=1796 h RJO 189M TOS=1796 h RJO 189P TOS=3547 h RJO 189P TOS=3547 h 11 Summary The full width at half maximum of the magnetite peak does not change significantly over the course of this run. This implies that there is no appreciable coarsening or grain growth of the magnetite phase. Examination of the peak areas of various magnetite peaks shows that the relative size of the peak at 2.099 is greater than that in the natural magnetite sample. This is due to overlap between the carbide and magnetite. As a first guess, these results would indicate that there is no significant transformation of carbide into magnetite over the course of the 3000 hour run. Had there been a transformation, the magnetite peak ratios should have approached those of natural magnetite as carbide was progressively converted into magnetite. There are important differences between the XRD patterns of these samples and those from the run performed at Texas A&M despite similarities in the operating conditions and pretreatment: 1. There are significant amounts of magnetite in the CAER samples while the amount of magnetite in the Texas A&M samples is negligible. The wax removal at Texas A&M is performed under an inert blanket while an inert blanket is not used during removal of the hot wax at CAER for this particular run. The role of the wax removal procedure on the relative amounts of magnetite and carbide need to be explored. The carbide peaks are well defined and show more lines than those in the CAER samples. Is this a result of these being different carbides or is it caused by difference in the extent of oxidation. We also do not have a sample of the catalyst after reduction and therefore do not know the extent of transformation to α-Fe during the reduction step. It would help to obtain a sample of this catalyst after the 220 °C H 2 activation so we could determine the phases present at the start of the run. If this reduction is performed for generating this sample, it would be useful to obtain sample with and without an inert blanket during discharge of the hot wax so that we can get an assessment of the extent of catalyst oxidation during wax discharge. 2. The loss of activity seems to be related to the increased crystallinity of the sample with time on stream. The peak intensity appears to increase with the XRD peaks becoming more well defined. This could be a result of the crystallite growth which would lead to loss of surface area. The peak widths of the magnetite peak do show a slight decrease in peak broadening with time on stream. However, at these particle sizes, particularly with the possible effects of lattice strain in the carbide, it may be best to resort to TEM analysis to infer the particle size changes. Future Work In future work, we will examine the wax stripped samples from these runs to derive detailed morphological information by electron microscopy. We would like to obtain from CAER a sample in wax after H 2 treatment under the conditions used in this run with and without an inert blanket. This will allow us to assess the extent of catalyst oxidation during wax removal and also establish the initial phase composition of this catalyst. 1

Platinum-Gallium (Pt-Ga) Intermetallic Alloys for Propane Dehydrogenation

Natural gas is a source of energy for the United States. The Center for Innovative Strategic Transformation of Alkane Resources (CISTAR) plans to use shale gas extracted from shale rock formations as a bridge fuel to replace coal and oil while the US transitions to renewable energy like solar and wind. After methane, the largest components in shale gas are light alkanes such as ethane and propane. These can be catalytically converted to olefins, which can be further reacted to produce fuels, for example. Olefins from alkanes can be accomplished by dehydrogenation by promoted platinum alloys. This study compares the structure and chemical properties of Pt-Ga alloys on silica (SiO2) and ceria (CeO2) supports to determine if the support plays an important role in this chemistry. The catalysts containing different Pt:Ga ratios were synthesized using incipient wetness impregnation. These catalysts were characterized by in situ X-ray diffraction (XRD) and X-ray adsorption spectroscopy (XAS) to determine if an alloy was formed, and if so, the structure of that alloy. Finally, the catalysts were tested in a fixed bed reactor, where it was found that the silica-supported Pt-Ga alloy has a selectivity of \u3e90% towards propylene. Understanding catalyst design can lead to higher catalytic conversion of substances and potentially an improved selectivity for the formation of preferred products. Pt-Ga on ceria is tested for comparison and there appears to behave differently from that on silica demonstrating the importance of the role of the support on these catalysts

EMSL and Institute for Integrated Catalysis (IIC) Catalysis Workshop

Within the context of significantly accelerating scientific progress in research areas that address important societal problems, a workshop was held in November 2010 at EMSL to identify specific and topically important areas of research and capability needs in catalysis-related science

Catalysis for the Conversion of Biomass and Its Derivatives

Biomass will play an important role in the future for the replacement of fossil sources for fuels and chemicals. Catalytic processes are required for the efficient conversion of biomass. The development of such processes and the understanding of the catalytic reactions of biomass molecules has recently attracted considerable and increasing attention. In this book, thirteen experts in different fields deliver their views on the state-of-the-art and future development of the use of biomass as a sustainable feedstock for the chemical industry. The book focuses on chemical aspects, such as catalyst development product analysis or reaction engineering, but also seeks a wider perspective and convers related issues like bioeconomics and plant growth. This book is aimed at students and scientists in the interdisciplinary field of catalysis for an introduction to the emerging field of biomass conversion and an overview on recent developments and challenges. The papers are based on lectures presented by the authors at a summer school organized by the Fritz-Haber-Institut and held in August 2010 at Kloster Seeon in Germany in the framework of the National Science Foundation-funded program Partnership in International Research and Education: Molecular Engineering for the Conversion of Biomass Derived Reactants to Fuels, Chemicals, and Materials