Preparation of silicon foam supported CoMn catalysts and their catalytic performances in higher alcohol synthesis via syngas

XRD patterns of the catalysts were acquired on a D8 Advance Bruker AXS diffractometer (40 kV,40 mA) with Cu Kα radiation (λ=0.15418 nm) from 5° to 90° at a scanning rate of 5°/min.The surface area of the catalysts was acquired by using N2 adsorption-desorption isotherms (BELSORP MAX Ⅱ) and calculated by using the BET equation. The pore volume and average pore diameter of the catalysts was calculated through the Barrett-Joyner-Halenda equation.TEM images of the catalysts were taken on the TecnaiG2 F20 S-TWIN TMP.The XPS spectra of the catalysts were acquired on the Thermo Scientific K-Alpha+ photoelectron spectrometer using a Kα aluminum X-ray source (hυ=1486.6 eV) under ultrahigh vacuum (approximately 8 × 10-10 Pa). All the binding energies of the elements were calibrated through the C 1s peak at 284.80 eV.ICP was performed to determine the elemental contents of each sample, and the tests were carried out on a ICAP 6300 inductively coupled plasma atomic emission spectrometer.The H2-TPR experiment was acquired using a BELCAT II instrument. Before testing, the catalyst (0.05 g) was loaded into a quartz tube and purged under Ar flow (30.0 ml/min) at 250 ℃ for 1 h, then cooled to 50℃. Then the gas was switched to 10% H2/N2 (30.0 ml/min). As long as the baseline attained stable, the temperature was increased from 50 ℃ to 800 ℃ with a heating rate of 10 ℃/min in the 10% H2/N2 (30.0 ml/min), and the off-gas was monitored by a thermal conductivity detector (TCD).The catalytic performance was evaluated in a stainless-steel fixed bed reactor. Typically,1.50 mL catalyst diluted with 1.50 mL quartz granules were loaded into the reactor. The specific experimental steps are shown below:Catalyst reduction: the catalyst reduced in situ under syngas (H2/CO=2.0) flow (80 mL/min) at 450 ℃ with a heating rate of 1 ℃/min for 8 h at atmospheric pressure. Then, the reactor was cooled down to room temperature. Catalyst evaluation: the reactor was pressurized to 5 MPa with a syngas (H2/CO=2.0) and GHSV of 4500 h-1. The temperature was increased to the target reaction temperature using a heating rate of 1 ℃/min. The liquid phase products generated after the reaction were collected by hot and cold traps, respectively. The carbon and mass balance were kept in the range of 95% and105%. To ensure the experiment's reliability, each sampling interval was set at 12 hours. The raw gas and tail gas were analyzed off-line by a beifen gas chromatograph equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Carbosieve-paced column and a TCD with Ar as the carrier gas were applied to analyze the CO、CO2、H2、CH4. The C1-C4 hydrocarbons were analyzed by an Al2O3 column and hydrogen FID using Ar as the carrier gas. The data were processed using the methane correlation method. The liquid phase products were separated into two phases: alcohol-water phase and oil phase. The alcohol-water phase products obtained from cold trap and hot trap were analyzed off-line by using an Agilent 7890B GC. The oil phase products obtained from cold trap and hot trap were analyzed off-line by using an Haixin GC-920. The alcohol-water phase products were analyzed through a DB-FFAP capillary column with FID and TCD (N2 as the carrier gas). The data were processed using the methanol correlation method.