Iron catalyst supported on carbon nanotubes for Fischer-Tropsch synthesis : experimental and kinetic study

The main objectives of the present Ph.D. thesis are comprehensive studies on activity, selectivity and stability of iron catalysts supported on carbon nanotubes (CNTs) for Fischer-Tropsch (FT) reactions. In order to prepare iron catalyst supported on CNTs, it was necessary to study CNT synthesis in bulk scale. Therefore, a part of this research was devoted to the production and characterization of CNTs. High purity, aligned films of multi-walled carbon nanotubes were grown on quartz substrates by feeding a solution of ferrocene in toluene, in a carrier gas of Ar/H2, into a horizontal chemical vapour deposition (CVD) reactor. Results for CNTs synthesized using a wide range of toluene concentrations indicated that, for carbon concentrations higher than ~9.6 mol/m3, catalyst deactivation occurs due to encapsulation of iron metal particles. As the first step of catalyst development for FT reactions a fixed bed micro-reactor system was built and the effects of acid treatment on the activity, product selectivity and stability of iron Fischer-Tropsch catalysts supported on carbon nanotubes were studied. The results of Raman analysis showed that the acid treatment increased the number of functional groups as anchoring sites for metal particles. Fe catalysts supported on CNTs which were pre-treated with nitric acid at 110°C were more stable and active compared to the un-treated catalysts. In order to study the effects of catalytic metal site position on FT reactions, a method was developed to control the position of the deposited metal clusters on either the inner or outer surfaces of the CNTs. According to the results of the FT experiments, the catalyst with catalytic metal sites inside the pores exhibited higher selectivity (C5+ = 36 wt%) to heavier hydrocarbons compared to one with sites on the outer surfaces (C5+ = 24 wt%) . In addition, deposition of catalytic sites on the interior surfaces of the nanotubes resulted in a more stable catalyst. The effects of pore diameter and structure of iron catalysts supported on CNTs on Fischer-Tropsch reaction rates and selectivities were also studied. In order to examine the effects of pore diameter, two types of CNTs with similar surface areas and different average pore sizes (12 and 63 nm) were prepared. It was found that the deposition of metal particles on the CNT with narrow pore size (in the range of larger than 10-15 nm) resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion. Promotion of the iron catalyst supported on CNTs with Molybdinium in the range of 0.5-1 wt % resulted in a more stable catalyst. Mo improves the stability of the iron catalyst by preventing the metal site agglomeration. Promotion of the iron catalysts with potassium increased the activity of FT and water-gas-shift reactions and the average molecular weight of the hydrocarbon products. Promotion of the iron catalyst supported on CNTs with 0.5% Cu and 1wt% K resulted in an active (5.6 mg HC/g-Fe.h), stable and selective catalyst (C5+ selectivity of 76%) which exhibited higher activity and better selectivity compared to the similar catalysts reported in the literature. Kinetic studies were conducted to evaluate reaction rate parameters using the developed potassium and copper promoted catalyst. It was found that the CO2 inhibition is not significant for FT reactions. On the other hand, water effects and presence of vacant sites should be considered in the kinetic models. A first-order reaction model verified that the iron catalyst supported on CNTs is more active than precipitated and commercial catalysts. The results of the present Ph.D. thesis research provide a map for designing catalysts using carbon nanotubes as a support. The key messages of the present thesis are as follows: 1- If the interaction of the metal site and support is strong, which poses negative effects on the catalytic performance, carbon nanotubes can be one solution. 2- Acid pre-treatments are required prior to impregnating nanotubes with metal salt solution. Also, the strong acid treatment should be used for deposition of catalytic sites inside the pores of nanotubes. 3- The structure and pore size of nanotubes have significant influence on the stability, activity and selectivity of the target catalyst. 4- The position of the catalytic sites has to be selected based on the type of reaction. In the case of Fischer-Tropsch reactions, the deposition of catalytic sites inside the pores of nanotubes results in higher activity, longer life span. The outcome of this Ph.D. thesis has been published/submitted in the form of 13 journal papers, one patent, one technical report and presented at 11 conferences

Non-IgE-mediated Gastrointestinal Food Allergy in Children: Our Foods and Atopy Patch Test

Abstracts:Background: Food allergy is an increasing health problem in children. Previous studies have reported conflicting results about the diagnostic value of atopy patch test (APT) in food allergies.Objectives: To investigate the accuracy of APT in identifying non-IgE-mediated gastrointestinal food allergy to pasteurized cow's milk, heated cow's milk, white and yolk egg, soy, wheat, walnut, sesame, pistachio, almond, peanut, date and cumin which are popular food ingredients in Iran.Methods: This study was performed on children with GI allergic problems who did not improve after at least 4 weeks of cow's milk protein elimination. Atopic patch test (APT) was performed and the elimination diet was considered according to APT results and after resolving symptoms, introduction of each accused food was done sequentially. Results: 53 children under 7 years old with mean age of 19.6 months underwent APT and the results were verified by open oral food challenge. Sensitivity in the rage of 59%-95%, specifity of 80.7-92.8, positive predictive values of 75-96.4 and negative predictive value of 23-80.7% were calculated depending on the type of food. Compared to the heated raw cow's milk, the pasteurized/homogenized cow's milk reaction was significant. Conclusion: APT can be included in the diagnostic workup of non-IgE-mediated GI allergy because it's safe and has great accuracy. However, several aspects require further investigation especially to enable the standardization of the technique. We should be aware of allegenicity of our foods due to processing and geographic region

A prototype compact accelerator-based neutron source (CANS) for Canada

Canada\u27s access to neutron beams for neutron scattering was significantly curtailed in 2018 with the closure of the National Research Universal (NRU) reactor in Chalk River, Ontario, Canada. New sources are needed for the long-term; otherwise, access will only become harder as the global supply shrinks. Compact Accelerator-based Neutron Sources (CANS) offer the possibility of an intense source of neutrons with a capital cost significantly lower than spallation sources. In this paper, we propose a CANS for Canada. The proposal is staged with the first stage offering a medium neutron flux, linear accelerator-based approach for neutron scattering that is also coupled with a boron neutron capture therapy (BNCT) station and a positron emission tomography (PET) isotope production station. The first stage will serve as a prototype for a second stage: a higher brightness, higher cost facility that could be viewed as a national centre for neutron applications

Association of social jetlag with gestational diabetes: Qazvin Maternal and Neonatal Metabolic Study

The association of social jetlag (SJL), as a quantitative measure of circadian misalignment, with insulin resistance and metabolic syndrome has been reported. The present study was designed to investigate the association of SJL with gestational diabetes mellitus (GDM). Pregnant women with gestational age ≤14 weeks were enrolled in this longitudinal study. The participants with pre-GDM, shift workers and those who used alarms for waking up on free days were excluded from the study. SJL as well as behavioral and psychological parameters were evaluated at enrollment. The participants were categorized based on each 1-h increment of SJL. The association of SJL with the occurrence of GDM in the late second trimester was evaluated using univariate and multivariate methods. In total, 821 pregnant women entered the study, and after omitting individuals with excluding criteria, analyses were performed on 557 participants. The frequencies of SJL < 1 h,1 ≤ SJL < 2 h and SJL ≥ 2 h were 44.7%, 37.2% and 18.1%, respectively. Average sleep duration was higher in SJL < 1 h compared with the two other groups (p < 0.001). During follow-up, 90 (16.1%) women with GDM were identified. SJL ≥ 2 h was associated with a 4.4-5.6 times higher risk of GDM in different models of adjustment (p < 0.05). Pregnant women with high SJL are at a higher risk of GDM. Further studies for evaluating the mechanisms by which SJL affects GDM are warranted

A review of advanced catalyst development for Fischer-Tropsch synthesis of hydrocarbons from biomass derived syn-gas

Fischer-Tropsch synthesis (FTS) is a process which converts syn-gas (H2 and CO) to synthetic liquid fuels and valuable chemicals. Thermal gasification of biomass represents a convenient route to produce syn-gas from intractable materials particularly those derived from waste that are not cost effective to process for use in biocatalytic or other milder catalytic processes. The development of novel catalysts with high activity and selectivity is desirable as it leads to improved quality and value of FTS products. This review paper summarises recent developments in FT-catalyst design with regards to optimising catalyst activity and selectivity towards synthetic fuels

Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), CO-chemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions

Towards Carbon Neutral CO2 Conversion to Hydrocarbons

With fossil fuels still predicted to contribute close to 80 % of the primary energy consumption by 2040, methods to limit further CO2 emissions in the atmosphere are urgently needed to avoid the catastrophic scenarios associated with global warming. In parallel with improvements in energy efficiency and CO2 storage, the conversion of CO2 has emerged as a complementary route with significant potential. In this work we present the direct thermo‐catalytic conversion of CO2 to hydrocarbons using a novel iron nanoparticle–carbon nanotube (Fe@CNT) catalyst. We adopted a holistic and systematic approach to CO2 conversion by integrating process optimization—identifying reaction conditions to maximize conversion and selectivity towards long chain hydrocarbons and/or short olefins—with catalyst optimization through the addition of promoters. The result is the production of valuable hydrocarbons in a manner that can approach carbon neutrality under realistic industrial process conditions