DOI: 10.15125/bath-00616
title: Dataset for: N-doped Fe@CNT for combined RWGS/FT CO2 hydrogenation

description: This dataset contains the experimental data used to generate the results and analysis published in "N-doped Fe@CNT for combined RWGS/FT CO2 hydrogenation" by Williamson et al. The data was collected between 2015 and 2019 to investigate the influence of nitrogen doping in the catalyst support of CNT-supported iron nanoparticles for the conversion of CO2 into hydrocarbon fuels.
description: Catalyst synthesis was achieved as follows: To produce Fe@CNT, 1.0 g ferrocene (FcH) was dissolved in 50 mL toluene to produce a CVD precursor solution of concentration 20 mg mL-1 FcH in toluene. 40 mL of the precursor solution was then injected at a rate of 10 mL h-1 into a quartz tube (25 mm ID x 28 mm OD x 122 cm L), loaded in a tubular furnace at 790 °C under a flow of 50 sccm H2 and 400 sccm Ar. After 4 hours of CVD injection, the raw catalyst was readily retrieved from within the quartz tube by scratching the interior cavity of the quartz tube with an elongated spatula. A 40 mL injection synthesis typically yielded ca. 1.5 g of catalyst. To produce Fe@NCNT, the same procedure was employed while replacing toluene in the precursor solution with acetonitrile (ACN) to act as a source of both carbon and nitrogen during the CNT growth process. To minimize error due to variance between catalyst batches, a stock of ca. 10 g was produced before beginning catalytic trials, and topped up every 3 reactions. 0.5 wt. % Na doping was achieved in Na-Fe@NCNT via wet impregnation. 9 mg NaHCO3 (Sigma-Aldrich, 99.7%) was dissolved in 15 mL deionized water with 0.5 g Fe@NCNT. The slurry was stirred for 24 hours and subsequently heated at 115 °C for 2 hours before collecting the dried powder.
Catalysts activation was achieved by loading 0.47 g of the into a stainless steel calcination tube (0.5 inch OD x 0.451 ID x 6 inch L).  This tube was plugged at one end with quartz wool (9-30 micron, H. Baumbach & Co Ltd) to prevent the catalyst from escaping while still allowing for air flow.  For Fe@ NCNT-based materials, the tube was then heated in a muffle oven at 400 °C for 1 hour under a static air atmosphere, with a heating ramp rate of 10 °C min-1. For any Fe@CNT-based materials, the same process was repeated, though the catalysts were instead heated to 570 °C for 40 min. Further information on the origin of these different activation temperatures can be found in the ESI.
CO2 conversion testing was conducted by loading 0.4 g of the desired catalyst into a stainless steel reaction tube (0.5 inch OD x 0.451 inch ID x 6 inch L), which was plugged with quartz wool (9-30 micron, H. Baumbach & Co Ltd) at both ends to ensure that the catalyst powder rested securely in the middle of the tube. The sample was then placed in a tubular furnace and heated to 400 °C for 3 hours under a flow of 50 sccm H2 to reduce the catalyst. To begin the combined RWGS/FT process, the temperature was lowered to 370 °C and the was pressure gradually raised to 15 bar while maintaining the desired reaction gas ratio (3:1 H2:CO2).  A high overall flow rate (180 sccm) was employed during this step to facilitate pressurization of the reactor. When the desired pressure had been achieved, the flow rate was lowered to the reaction flow rate of 8 sccm.  The reactor was left for 2 hours to equilibrate following pressurization, after which samples were taken hourly for 3 hours via a 50 mL SGE gas tight syringe with leur-lock fittings and analyzed via GC-MS. An Agilent Technologies 7890A GC System with Agilent Technologies 5975C insert MSD with Triple-Axis Detector (MS, TCD, FID) was used as the GC-MS instrument.  The installed column was an HP-Plot Q column. The TCD was used to quantify CO2 and CO, while the FID was used to quantify hydrocarbon species. 1% Ar in H2 was used as the source in CO2 conversion experiments so that Ar could be used as an internal standard during GC-MS measurements. 
It should be noted that the chosen reaction conditions have been previously identified as producing noteworthy CO2 and CO conversion over Fe@CNT-type materials.15 However, the stated flow rate of 8 sccm should be considered low for the tested catalyst powder mass of 0.4 g. Diffusion limitations may play a role in masking the intrinsic activity of the catalyst and conditions at the catalyst surface. Further work must be conducted to optimize the reaction process.
Catalyst characterization was achieved with Raman, TEM, XPS, XRD, and TPD. Raman analysis was conducted using a Renishaw InVia system with a 532 nm laser.  For CNT-based materials, a laser power of 5% was employed with the standard exposure time to facilitate quick analysis without burning or damaging the sample during analysis.  For NCNT-based materials, the laser power was reduced to 0.1% due to the decrease in the stability of the CNT lattice caused by nitrogen doping leading to significant decomposition under even 1% laser power.  Consequently, the exposure time for NCNT-based samples was also increased substantially to 400 seconds to collect a clear Raman spectrum. TEM analysis was conducted using a JEOL JSM-2100PLUS at an accelerating voltage of ca. 200 kV. Particle and tube diameters were measured using the open source image processing package Fiji. XPS analysis was conducted using a Kratos Axis Ultra-DLD system. Samples were analyzed using a micro-focused monochromatic Al X-ray source (72 W) over an area of approximately 400 microns. Data was recorded at pass energies of 150 eV for survey scans and 40 eV for high resolution scan with 1 eV and 0.1 eV step sizes respectively. Charge neutralization of the sample was achieved using a combination of both low energy electrons and argon ions. XRD analysis was conducted using a Bruker D8 Advance with Vantec Detector using Cu K-α1 radiation was used to analyze all samples, which were scanned in flat plate mode from 20-80° at a scan rate of 0.27° min-1 (4 hours per sample). H2, CO and CO2 TPD analysis were conducted using a Micrometrics AutoChem II 2920 V4.03 Automated Catalyst Characterization System with Thermal Conductivity Detector (TCD). Samples were subjected to temperature programmed reduction up to 1000 °C at 10 °C min-1 (50 sccm 5% H2 in Ar), pulse chemisorption of the desired analysis gas (50 sccm, 5% in He) and subsequent TPD. A detailed simulation methodology for the molecular dynamics simulations can be found in the ESI.
description: Data processing was conducted using Microsoft Excel. The document used for processing of GC-MS data is attached here. Particle sizes were measured using the ImageJ image processing package from TEM images.