Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer–Tropsch Synthesis and Reductive Hydroformylation

Abstract The selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer–Tropsch and molecular hydroformylation catalysts in a one‐pot slurry‐phase process. Unprecedented selectivities (>50 wt %) to C2+ alcohols are achieved at CO conversion levels >70 %, alongside negligible CO2 side‐production. The efficient overall transformation is enabled by catalyst engineering, bridging gaps in operation temperature and intrinsic selectivity which have classically precluded integration of these reactions in a single conversion step. Swift capture of 1‐olefin Fischer–Tropsch primary products by the molecular hydroformylation catalyst, presumably within the pores of the solid catalyst is key for high alcohol selectivity. The results underscore that controlled cooperation between solid aggregate and soluble molecular metal catalysts, which pertain to traditionally dichotomic realms of heterogeneous and homogeneous catalysis, is a promising blueprint toward selective conversion processes.


N2 physisorption porosimetry
N2 physisorption isotherms of porous solids were recorded at 77 K using a Micromeritics 3Flex V4.04. Prior to the measurements, samples were dried in situ at 523 K under vacuum (10 -3 mbar) for 12 h (10 K min -1 ). The Brunauer-Emmett-Teller (BET) method was used to determine surface areas from the 0.05-0.30 P/P0 regime of the recorded isotherms. Pore volumes were determined from the adsorbed N2 volume detected at equilibrium point P/P0 of 0.95 in the adsorption branch of the isotherm. Pore size distributions were determined using the Barrett-Joyner-Halenda (BJH) method applied to the desorption branch of the isotherm. The average mesopore diameter was defined as the peaking value of the pore size distribution.

Hg intrusion porosimetry
Mercury intrusion porosimetry experiments were performed in a Micromeritics AutoPore IV 951 apparatus. 80-150 mg of the solid sample (0.08-0.10 mm sieve fraction) were dried at 383 K for 72 h before the measurement.
The intrusion-extrusion isotherms were recorded at room temperature in the pressure range of 6.9•10 4 -4.1•10 4 Pa with an equilibration rate of 0.1 μL g -1 s -1 . For the determination of pore diameter and volume, a geometrical pore model was considered, with a Hg density of 13.55 g cm -3 and a contact angle of 141 degree.

H2-Temperature-programmed reduction
Hydrogen temperature-programmed reduction (H2-TPR) experiments were conducted to assess the reducibility of metal species in supported FTS catalysts and select the temperature for the H2-reduction treatment applied prior to catalysis to render the metal in its FTS-active metallic state. Experiments were performed in a Micromeritics Autochem 2910 device. About 45 mg of sample (0.08-0.10 mm sieve fraction) were initially S5 flushed with Ar flow (50 cm 3 min -1 ) at room temperature for 30 min, then the gas was switched to 10 vol% H2 in Ar and the temperature increased up to 1123 K at a heating rate of 10 K min -1 . A downstream acetone/dry ice trap, located downstream of the U-shaped tubular reactor, was used to retain the water generated during the reduction. The H2 consumption rate was monitored by a thermal conductivity detector (TCD) previously calibrated via the injection of known volumes of hydrogen using a gas syringe. The cobalt loading in the catalysts was determined from the total hydrogen consumption assuming all cobalt to be present as Co3O4 in the starting calcined catalysts (as confirmed with powder X-ray diffraction experiments, not shown). Therefore a reduction stoichiometric H2:Co molar ratio of 4/3 was applied. The hydrogen consumption associated to the reduction of the Ru promoter was considered negligible. Figure EM1 shows the H2-TPR profiles registered for CoRu/AOm and NaPr-CoRu/AOmM Fischer-Tropsch synthesis catalysts. Reduction events peaking at 480-540 K and 650-660 K, respectively, were observed, corresponding to the two-step reduction of Co3O4 to metallic Co. In view of these reduction profiles, a reduction temperature of 673 K was selected to activate the FTS catalysts in this study prior to catalysis testing.

H2 chemisorption
Surface-exposed metal surface areas in supported solid FTS catalysts were determined using H2 chemisorption uptakes at 373 K by plateau extrapolation to zero H2 pressure. [1] Experiments were performed in an ASAP 2010C Micromeritics device. Prior to H2 dosing, the oxidic sample (ca. 0.1 g of supported cobalt catalyst) was reduced in situ under flow of pure H2 at 673 K for 5 hours (heating rate from RT of 2 K min -1 ). After reduction, the sample was degassed at 1.3 Pa and the temperature lowered to 373 K to record the H2 chemisorption isotherm.
Co 0 surface areas were determined from the total amount of chemisorbed H2, and the Co loading as determined by H2-TPR. The contribution of Ru 0 to the overall metal content was considered insignificant. A surface H/Co=1 stoichiometry and a surface atomic density of 14.6 Coat nm -2 were considered.

Chemical analysis by Energy-dispersive X-ray spectroscopy (EDS)
In order to quantify bulk promoter contents in promoted FTS catalyst samples, energy-dispersive X-ray spectroscopy (EDS) was performed on a Hitachi S-3500N scanning electron microscope. The powder sample was ground and then applied onto a pin-stub SEM mount coated with double-adhesive-face conductive carbontab. EDS spectra of areas of 1 mm 2 were scanned using an Oxford Pentafet 10 mm 2 detector to make sure a statistically relevant number of catalyst particles was jointly analyzed.

Tomographic Focused-Ion-Beam Scanning-Electron Microscopy (FIB-SEM)
Catalyst microparticles (80-100 μm) were embedded in a low-viscosity epoxy resin (Spurr) and the resin cured at 343 K for 12 h. The resin-embedded sample block was then trimmed and polished in an ultramicrotome (Reichert Ultracut) using first a glass knife (coarse trimming) followed by a fine trimming with a diamond knife (Diatome). Finally the trimmed specimen was mounted on a SEM stub with conductive colloidal graphite adhesive. The stub-mounted sample was sputter-coated with a ca. 20 nm carbon overlay using a LEICA EM MED020 sputter coater to achieve full conductive joints and minimize local charging artefacts during SEM imaging. Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) experiments were performed in a Zeiss Auriga Compact dual-beam microscope. First, a protective Pt layer was deposited on the region of interest (ROI) using the gas injection system. Then, the Ga + ion gun, operated at an intensity of 10 nA, was used to mill a front and two lateral trenches, delimiting the volume to be imaged, as well as a cross fiducial marker on the top surface S7 of the ROI to be used for automated image recognition and drift correction during the slice-and-image procedure.
Serial sectioning combined with SEM imaging was carried out with specimen drift and beam shift corrections.
Slices with nominal thickness of 60 nm were milled off using the Ga + FIB gun operated at an intensity of 3 nA.
The corresponding SEM micrographs of the consecutively exposed cross-sections were recorded with a secondary electron detector while the electron gun was operated at a voltage of 2 kV.
The stack of raw micrographs was corrected for the foreshortening caused by the tilt angle between the specimen cross-section and the SEM detector (54° in the dual beam microscope employed in this study). Next, a stack deflicking filter was applied to correct inter-micrograph gray-value gradients within the stack of images. After stack alignment using an iterative cross-correlation algorithm, the reconstructed tomograms were segmented using a watershed algorithm in Imagej, [2] followed by fine adjustment of the automatically recognized volumes via controlled erosion-dilation functions, to remove artefact material "islands", as well as manual threshold adjustment to correct for local gray-scale gradients created by either curtaining effects or shadowing phenomena.
After tomogram binarization, a 3D local Euclidean distance transform [3] was propagated along the threedimensional skeleton of the "solid" alumina phase to quantify the shortest distances from any point within the mesoporous alumina domains to the nearest boundary to the macropore network in Avizo (Thermo Fischer Scientific), where volumes were also surface-rendered for 3D visualization. There so-derived Euclidean mesopore transport distances were corrected for a pore tortuosity (τ) factor estimated as = 1−(1− ) 2 3 ⁄ , [4] where ε is the void fraction of the material's mesoporosity derived from the mesopore volume as = 1 1+ 1 • , where ρ is the materials skeletal density and PVmeso is the mesopore volume as determined by Hg intrusion porosimetry.

High-Angle Annular Dark-Field Scanning-Transmission Electron Microscopy (HAADF-STEM)
HAADF-STEM was applied to image the nanostructure of solid FTS catalysts. Before microscopy observation, samples were embedded in a low viscosity resin (Spurr, hard composition) and hardened at 343 K. Then nanometer thin slices (nominal thickness of 150 nm) were obtained with a Diatome diamond knife mounted on a Reichert Ultracut ultramicrotome and collected on a copper TEM grid (300 mesh) covered with a lacey carbon film. High-angle annular dark-field (HAADF) STEM micrographs and Energy Dispersive X-ray Spectroscopy (EDS) elemental maps were acquired using a beam spherical aberration-corrected (Cs) Hitachi HD-2700 S8 dedicated Scanning Transmission Electron Microscope (STEM) equipped with a cold field-emission gun and two EDAX Octane T Ultra W EDS detectors (Ametek) and operated at 200 kV, and a Jeol JEM 2100F Scanning Transmission Electron Microscope (STEM) equipped with a X-Mac EDS detector (Oxford instruments) and operated at 200 kV.

Inductively-coupled-plasma mass-spectrometry and optical-emission spectroscopy.
Elemental (Co, Na, Pr) contents in selected reaction liquors were determined by inductively-coupled-plasma mass-spectrometry (ICP-MS). To digest the organic material, 10 mg of sample were mixed with 8 mL concentrated HNO3 and heated in a microwave oven (CEM, Mars 6) up to 200 °C (1500 W, temperature ramp of 30 minutes from RT). Afterwards the temperature was held for 15 minutes. After cooling down, the sample was filled up to 100 mL with H2O. After acid digestion, the sample was injected into the ICP-MS (ICPMS-2030, Shimadzu) and measured at least two times. Before each measurement, commercially available calibration standards (Carl Roth) for the target element, in the expected concentration range, where injected similarly. The metal/lanthanide concentration in the organic reaction liquors was determined by comparing the average of all measurements with the pre-measured calibration curve. The concentration in the liquor samples was referenced to the background concentration determined in a preparation blank solution that has been taken through an identical sample preparation procedure. The Na concentration in the preparation blank was already too high for a reliable determination by ICP-MS. Hence, Na analysis was also performed by inductivelycoupled-plasma optical-emission-spectroscopy (ICP-OES) in a iCAP PRO spectrometer (Thermo Scientific) calibrated with certified Na standards. The absence of Na leaching into solution was inferred from experimental Na concentrations in the liquid samples statistically identical to, or lower than, those in the preparation blank (0.2 ppm).

Nuclear Magnetic Resonance
The structure of molecular olefin reductive hydroformylation catalysts was assessed by 1 H[ 31 P] and 31 P[ 1 H] nuclear magnetic resonance (NMR) spectroscopy. For this, between 50 mg and 300 mg of the solution after the specific reaction procedure were transferred under inert atmosphere into a NMR young-tube and diluted with 200 mg to 500 mg of the selected deuterated solvent. Spectra were acquired on a 500 MHz NMR spectrometer (Bruker) equipped with an auto sampler at 293 K. 1 H[ 31 P]-NMR measurements were collected with at least 128 S9 scans each, in order to identify hydride signals of catalyst species in low concentrations.

Catalyst testing in the Fischer-Tropsch synthesis (FTS)
The catalytic performance of supported cobalt-based catalysts was assessed by means of gas-phase Fischer-Tropsch synthesis tests. The FTS catalytic tests were performed at 20 bar and 473 K in a fixed-bed reactor setup. The setup is equipped with mass-flow controllers (Bronkhorst, MFCs) to feed H2 (Air Liquide, 99.999%, CAS: 1333-74-0) and pre-mixed syngas (30 vol.% CO, 60 vol.% H2, 10 vol% Ar as internal standard, Air Liquide, 99.99%), two-finned copper elements with embedded 180 W heating cartridges to heat the stainless steel (316L grade) fixed-bed micro-reactor (inner diameter, i.d. = 12 mm), two thermocouples (K-type, 0.5 mm) placed at the start and at the end of the catalyst bed as part of two PID feedback loops to control the temperature inside the reactor, and an online gas chromatograph (modified Agilent 7890B) for product analysis.
Upstream of the syngas MFC, the syngas stream was first passed over an activated carbon bed (Norit) at 30 bar and room temperature to remove metal-carbonyl impurities that might be entrained from the pressurized gas cylinder, and then through a 316L grade stainless steel (length, l = 300 mm, i.d. = 3 mm inner diameter) capillary loop maintained at 473 K to pre-heat the syngas. The free volume in the reactor was reduced by inserting two 316L grade stainless-steel spacers, one (l = 62 mm) upstream of the catalyst bed, and another (l = 50 mm) downstream of the bed. The spacers were separated from the catalyst bed using two quartz wool plugs (l = 5 mm). Below the first quartz wool plug, a 3.4 cm 3 layer of SiC granules (Alfa Aesar, 46 grit, CAS: 409-21-2) was placed to additionally pre-heat syngas and help establish plug-flow before entering the catalyst bed. The catalyst bed consisted of an amount of catalyst equivalent to 180-300 mg of Co 0 as determined by H2-TPR.
Before the FTS tests, the metal species in the catalyst were reduced in H2 flow (200 cm 3 STP min −1 ) at 673 K (2 K min −1 to 423 K, followed by 0.83 K min −1 to 673 K) for 5 h at atmospheric pressure. This reduction temperature was selected on the basis of the H2-temperature programmed reduction profiles registered for the herein reported FTS catalysts ( Figure EM1). Following catalyst reduction activation, the reactor was cooled to S10 hourly space velocity, WHSV = 3.6-11.0 h −1 ). The system was then pressurized to 20 bar using a membrane dome regulator (GO regulator), and the reactor temperature was increased to 473 K (0.15 K min −1 ). The start of the temperature ramp from 423 K to 473 K in syngas was marked as time-on-stream = 0 h. Both reactor design and startup protocols have been optimized to ensure an isothermal catalyst bed operation. After at least 24 h time-onstream, the syngas flow was adjusted to determine catalyst performance at a 20±3% CO conversion level.
Downstream of the reactor, two consecutive cold traps were set at temperatures of 423 K and 373 K at the reaction pressure to collect heavy hydrocarbon products and water. All other downstream tubing was heated to 443 K to prevent the condensation of reaction products. All gaseous components of this gas stream leaving the traps were depressurized after passing the dome pressure regulator and were analyzed by online gas chromatography. The gas chromatograph is equipped with two sampling loops, one of which feeds into a capillary column (Restek RTX-1, 60 m) equipped with an FID detector, while the other feeds into two consecutive packed-bed columns (HS-Q 80/120, 1x m + 1x 3 m) equipped with a TCD for the analysis of H2, CO2, and C2-C3 hydrocarbons. Along this analysis channel, a molecular sieve column is used for the separation of Ar, CH4, and CO, which are detected using an additional TCD. Figures EM2 and EM3 show representative product chromatograms obtained online for the gas product stream collected while testing a dually promoted NaPr-CoRu/AOmM meso-macroporous CoRu/γ-Al2O3 catalyst. CO, CH4, and CO2 were quantified using TCD response factors relative to Ar, whereas for usual tests C2+ hydrocarbons and alcohols were quantified in the FID relative to CH 4. CO conversion (XCO) and the metal-specific reaction rate (cobalt-time-yield (CTY)) were used to express catalytic activity (Equations 1 and 2). Selectivity to C5+ hydrocarbon products was determined by deducing the selectivity to C4-carbon-containing products, including CO2, from a closed carbon balance (Equations 3 and 4). Liquid and solid hydrocarbons collected from the trap kept at 373 K and 20 bar were separated by decanting, the individual liquid phases were further purified by centrifugation (9000 rpm, 15 min) to collect waxes and obtain clear polar and non-polar phases which were weighed separately. Solid wax hydrocarbons collected from the trap kept at 423 K and 20 bar were blended together with those wax fractions collected by centrifugation of the liquid products, weighed, and dissolved in CS2 (≥99%, Sigma-Aldrich, CAS: 75-15-0). Acetone (HPLC grade, ≥99.9%, Sigma-Aldrich, CAS: 67-64-1) was added in the case of aqueous phase samples and 2-methyl heptane (>98.0%, Sigma-Aldrich, CAS: 592-27-8) was added in the case of nonpolar oil and wax solution samples as gas chromatography standards, respectively. Offline gas chromatography of the organic hydrocarbon samples was performed on a second Agilent 7890B gas chromatograph equipped with a capillary column (Restek RTX-1, 60 m) which elutes into an FID. Offline gas chromatography of S11 aqueous phase products was performed on a third Agilent 7890B gas chromatograph equipped with a highpolarity polyethylene glycol (DB-Waxetr, iD=0.25 mm, film thickness=0.25 µm, 30 m) which elutes into an FID. Carbon balances closed at 96.5±2.0%. For catalyst reuse tests, following a first tandem FTS/RHF reaction run (24 h), the reaction liquors were removed from the reactor through an immersion capillary equipped with a (Type 113P, 5-8 µm, Carl Roth GmbH) filter to retain solid particles, also employing a riser tube to enable gas flow. Liquor removal was performed at the reaction temperature (hot filtration) to provide a fair assessment of catalyst stability, avoiding artifacts associated to possible metal re-deposition phenomena upon cooling the reaction slurry. The solid catalyst was recovered and reused for a second FTS/RHF test after replenishing the reactor inlet with fresh solvent, RHF catalyst, and syngas. All tasks were performed under air exclusion in an Ar-filled glovebox to prevent metal re-oxidation. No catalyst rejuvenation/regeneration treatment was applied between the consecutive runs. Following the second run, the exact amount of FTS catalyst was determined in order to correct activity values for any loss of FTS catalyst during filtration and re-slurrying between runs. To this end, the solid was isolated by ultracentrifugation and the catalyst mass determined as the solid residue by TGA.   antechamber replenished, and the reactor sealed and re-pressurized again to the initial total pressure of 120 bar with the synthetic syngas mixture. In either case, following syngas dosage, the autoclave was heated to the desired reaction temperature (typically 473 K) in a (preheated) aluminum block fitted on a magnetic stirrer.
Reaction was let to proceed in batch mode under vigorous magnetic stirring (700 rpm). Once the reaction time had elapsed, the autoclave was allowed to cool to RT.
The headspace gas was analyzed by releasing a portion of the gas phase after the reaction to flush and fill two sampling loops of an Agilent 7890B gas chromatograph (GC) connected in series. One of those sampling loops is then injected into a capillary column (Restek RTX-1, 60 m) that elutes into a Flame-Ionization detector (FID), while the other sampling loop is injected into two consecutive packed-bed columns (HS-Q 80/120, 1x m + 1x 3 m), that elute into a Thermal-Conductivity detector (TCD) for H2, CO2, and C2-C3 hydrocarbons quantification. Further down that analysis channel, a molecular sieve column (13X) separates Ar, CH 4 , and CO S16 permanent gases, by means of a second TCD. After sample injection, the GC oven temperature was kept at 308 K for 10 min, after which the oven was heated to 483 K (heating ramp 283 K min -1 ). Then, the temperature was kept at 483 K for 45 min. CO, CH 4 , and CO 2 were quantified using TCD response factors relative to Ar, whereas C2+ hydrocarbons and alcohols were quantified in the FID relative to CH 4.
Condensed phases in the reactor after the reaction test were collected and then centrifuged in an ultracentrifuge at 13.000 rpm, after which the liquid and solid phases were separated and recovered separately. The liquid sample was injected into an Agilent 7890B GC equipped with a capillary column (Restek RTX-1, 60 m) which elutes into an FID. Following injection, the GC oven temperature was heated from RT to 493 K (heating rate 278 K min -1 ), after which the temperature was kept at 493 K for 50 min. Hydrocarbons and alcohols were quantified based on their FID signal relative to a known amount of iso-octane as internal standard.
For selected tests, the liquid product fraction was additionally analyzed by two-dimensional gas chromatography in a 2D GCxGC LECO Pegasus 4D chromatograph equipped with a flame ionization detector (FID) and a timeof-flight-mass spectrometer (TOF-MS) using an analysis protocol previously optimized for complex mixtures of hydrocarbons and higher oxygenates. [5] The system was operated in reverse phase configuration, where the first dimension is a polar column (Stabilwax) and the second dimension is a non-polar (RTX-5), see Table EM1 for detailed analysis conditions and column specifications. Modulation of the effluent from the primary column was achieved by cooling a dry N2 gas stream with liquid nitrogen. Data analysis was performed using the TOF Chrom software package. S17 The amount of waxy hydrocarbons in the solid pellet recovered after centrifugation was quantified by thermogravimetric analysis (TGA) in air using corundum crucibles in a Netzsch Jupiter STA 449 C thermobalance and exposing the sample to a heating ramp of 10 K min -1 from 298 K to 1023 K. The fraction of the total amount of combusted matter associated to waxy hydrocarbon products was estimated by subtracting catalyst. Wax contents determined this way were <2 C% in all cases. S18 Figure EM4: Representative gas-phase (headspace) product chromatograms for a tandem FTS/RHF catalytic test in slurry phase. a) Hydrocarbon products in the range of C1-C5 eluting from a Restek RTX-1 capillary column can be detected in the flame-ionization detector (FID) of the Agilent GC7890B. Permanent gases eluting from a 13X molecular sieve packed column are detected on a first TCD, whereas light hydrocarbon products (C2-C3), as well as CO2 and water eluting from two consecutive HS-Q 80/120 packed columns are detected on a second TCD.    Figure S3: Pre-catalyst species equilibria for the HCo(CO)3(PCy3) reductive hydroformylation catalyst. Adapted from [6] .   Figure S4, (ii)), respectively. Both complexes have been synthesized and isolated to confirm signal assignments, following procedures described by Wood and Garrou. [7] A singlet in very low concentrations at δ = 80.25 ppm remains unassigned.       As shown in Figure S12, following addition of the PCy3 ligand to a suspension of the solid NaPr-CoRu/AOmM Fischer-Tropsch catalyst and exposure to syngas conversion conditions for 24 h, the 1 H-NMR spectrum for the reaction liquor revealed the same hydride species at = -10.9 ppm which was identified earlier as [HCo(CO)3(PCy3)], even though no specific cobalt source had been added for the development of the RHF molecular catalyst. The presence of cobalt phosphorous species is confirmed in the corresponding 31 P-NMR spectrum. Besides free phosphorus ligand PCy3 and oxidized O=PCy3 in high concentrations, the hydride species [HCo(CO)3(PCy3)] and the dinuclear species [Co2(CO)6(PCy3)2] can be identified in the 31 P-spectrum. Even though at remarkably lower concentrations compared to the case where a specific cobalt carbonyl source is added into the reaction medium, the detection of these species, which take part in the RHF pre-catalyst equilibria ( Figure S3), suggests their development via ligation of a small fraction of cobalt species leached from the surface of the solid FTS catalyst. Electron microscopy was applied on the NaPr-CoRu/AOmM Fischer-Tropsch catalyst to assess any (nano)structural modifications brought about by its exposure to reaction conditions in the slurry-phase FTS/RHF process. The results are summarized in Figure S13. The catalyst particles preserved their intraparticle macroporosity (see panel a). Observation at high magnification revealed that the size and uniform spatial distribution of the Co nanoparticles within the mesoporous domains of the Al2O3 carrier had been preserved. EDS nanospectroscopy compositional maps revealed, however, a certain enrichment in cobalt close to the outer rim of the catalyst particles, alongside, few (scarce) large Co aggregates (see panels d and e), which are compatible with the deposition of cobalt from the molecular Co carbonyl catalyst and/or its decomposition/precipitation upon isolation and drying of the solid catalyst from the reaction liquors. Extensive EDS analyses did not reveal any relevant phosphorous content, reinforcing the stability of the molecular catalyst which remains by and large soluble after catalysis and it is therefore removed during the centrifugation workup applied to isolate the solid FT catalyst from the reaction liquors. Figure S14: FTS catalyst recycling. Catalyst performance for two consecutive FTS/RHF tandem reaction runs. The reaction liquors were hot filtered off the reactor following the first run, under a protective Ar atmosphere. The solid FTS catalyst was recovered and applied in a second reaction run without any rejuvenation/regeneration. FTS catalyst: NaPr-CoRu/AOmM; RHF catalyst: Co2CO8 + PCy3 (L:M=1.0 (P/Co, at/at)). Reaction conditions: T = 473 K, P= 120 bar (initial, measured at RT), solvent 2-methyl pentane, stirring rate 700 rpm, syngas feed H2:CO = 2. a C3-10 olefin selectivity ≤ 0.2 C% in all cases. Activity is normalized per unit metal mass (metalspecific time yield) to account for the fact that the solid FTS catalyst could not be recovered quantitatively from the cake formed on the filter during hot filtration after the first run. Figure S15: Three mechanistic proposals for the reductive hydroformylation of α-olefins produced in situ from syngas on a FTS solid catalyst: (i) alkyl-shift mechanism wherein the molecular cobalt carbonyl RHF catalyst intercepts α-C-bonded growing hydrocarbon chains from the surface of the Co nanoparticles on the FTS catalyst, prior to their desorption; (ii) desorption of αolefin primary products from the surface of the Co nanoparticles followed by their interception by the molecular cobalt carbonyl RHF catalyst immediately after desorption, within the pore-occluded liquid-phase; (iii) desorption of α-olefin primary products from the surface of the Co nanoparticles followed by pore transport, egression from the porosity of the FTS catalyst and conversion by the molecular cobalt carbonyl RHF catalyst in the extra-pore (continuous) liquid phase. For simplicity the scheme does not contemplate side reactions initiated via double-bond isomerization of FTS 1-olefins, and the full hydroformylation mechanism proposal is only showed for the case of the on-surface alkyl-shift.   As shown in Figure 4 (main text), time-resolved monitoring of the bifunctional process showed the CO conversion to increase essentially linearly with time to reach 70.1% after 72 h. A comparatively similar trend was observed with the FTS alone ( Figure S18 above), discarding any noticeable deactivation of the latter due to either the concomitant presence of the RHF catalyst or the increase in water content in the reaction medium at increasingly higher syngas conversion levels. Moreover, alcohol selectivity scaled steeply with time up to ca. 20 h, suggesting a transient induction period for RHF activity (Figure 4), to level off to ca. 50-53 C% at CO conversion levels in the range of 30-50%, and slightly decrease to just above 45 C% when the CO conversion was further increased to ~70%. It is surmised that this slight decrease in alcohol selectivity is associated to the drop in PCO to 12.1 bar observed at this syngas conversion level in the batch reaction system, i.e. lower than the critical PCO below which the molecular RHF catalyst offers suboptimal performance. Remarkably, a gradual and marked increase in n:iso ratio was observed for the alcohol products (from ca. 1.5 to >5.0) on increasing CO conversion up to >50% with the tandem catalysis system. (Figure 4). Meanwhile, identical experiments with the solid FTS as the sole catalyst ( Figure S18) showed constant alcohol selectivity of 27.3 ±3.2 C% and alcohol n:iso ratio of ca. 2 over the same syngas conversion span. In view of the pronounced effect which the L:M ratio has on the regioselectivity of the RHF reaction (Table S3), we surmise that a progressive increment in the effective ligand-to-cobalt ratio might underlie the trend observed for the higher alcohol regioselectivity in the tandem process, possibly as a result of a partial depletion of the molecular catalyst in Co upon the establishment of dissolution/deposition equilibria with the cobalt agglomerates on the FTS catalyst.  [9] . Selected performance data for the herein reported tandem FTS/RHF process have been added on the plot (red diamonds). Tables   Table S1: Reaction rate and product selectivities for the gas-phase Fischer-Tropsch synthesis (FTS) reaction (fixed-bed reactor) with CoRu-based FTS catalysts. Reaction conditions: T = 473 K, P = 20 bar, H2:CO = 2, CO conversion = 20 ± 3%.   [a] Initial, measured at RT. [b] Lumped selectivity to n-and iso-products. [c] linear-tobranched ratio for alcohol products. [d] Turnover number for alcohol production.

Supporting
The performance of the Co2(CO)8 + PCy3 catalyst was assessed for the reductive hydroformylation of 1-octene, as a model compound for mid-chain Fischer-Tropsch synthesis α-olefins. The reaction temperature of 468 K was selected for compatibility with the operation temperature typical for the FTS. As shown in Table S2, the catalyst showed high activity for the conversion of 1-octene, and full olefin conversion was achieved within 3 hours of reaction in all cases. Under a syngas pressure of 120 bar (corresponding to a CO partial pressure PCO of 40 bar) a high selectivity of 93% to alcohols was achieved. Under these conditions, the selectivity towards the full olefin hydrogenation product (1-octane) was very low (<1%). The suppression of this side-reaction, which is commonly observed in olefin reductive hydroformylation reactions, [10] is particularly relevant in the contest of the FTS/RHF tandem process. Decreasing the syngas pressure stepwise to 90, 60 and 30 bar (corresponding to PCO in the range of 30-10 bar) led to a decrease in alcohol selectivity and an increase in the selectivity to internal 1-octene isomer olefins. Below 60 bar of total pressure, the hydrogenation of the starting olefin is enhanced significantly. The deterioration of the product selectivity was particularly notorious when the CO partial pressure was decreased to 10 bar, where the selectivity to n-octane reached 9% and that to internal olefin isomers approached 70%. The syngas pressure had little influence on the regioselectivity of the alcohol products, for which the n:iso ratio remained within 1.3-1.6.
It is known that cobalt-based catalysts generally need comparatively high partial CO pressures than rhodiumbased catalysts in hydroformylation reactions. [11] Given that the Fischer-Tropsch synthesis is not substantially influenced by the total reaction pressure, a total initial syngas pressure of 120 bar was selected for the tandem FTS/RHF experiments. Reaction conditions: n(1-octene) = 9.3 mmol, V(iso-hexane) = 2.75 mL, H2:CO=2.0, P = 120 bar (initial, measured at RT), T = 468 K, t = 3 h. X = conversion, S = selectivity, M = metal, L = ligand. [a] Ligand-to-metal ratio, expressed as P/Co (at/at). [b] Cobalt concentration in the reaction medium relative to the initial 1-olefin substrate concentration. [c] Lumped selectivity to n-and iso-products. [d] linear-to-branched ratio for alcohol products.
[e] Turnover number for alcohol production.
Increasing the ligand-to-metal ratio from 1:1 to 10:1 resulted in a progressive and marked increase in the linearto-branched ratio for the alcohol products, from 1.4 up to 12, indicative for a progressively enhanced anti-Markovnikov regioselectivity and/or inhibited double-bond isomerization reactivity prior to olefin oxofunctionalization (Table S3, entries 3.1-3.4). With a ligand-to-metal ratio of 10:1, 1-nonanol accounts for more than 90% of the alcohols produced. Together with the increase in alcohol regioselectivity, an increase in the undesired direct olefin hydrogenation, alongside a reduced activity for the transformation of internal olefins, are observed, which lower the overall selectivity to alcohols. Literature describes a monocoordinated cobalt complex as the active catalyst for the cobalt-catalyzed hydroformylation reaction using monodentate trialkylphosphine compounds as ligands. [6a, 7] With higher ligand contents, the development of cobalt molecular species with higher ligand coordination degrees (higher substituted species) are considered to be sterically more demanding, which might induce higher regioselectivity, but not as active as the mono-substituted cobalt complex.
[6a] Moreover, the application of a ligand excess might lead to non-coordinated (free) phosphine species. Given that the Fischer-Tropsch catalyst is a well-defined metal surface, interaction between free phosphines and the FTS catalyst surface should be minimized. In view of the higher overall selectivity to alcohols and the expected benefits of a minimum concentration of free ligands in the medium, a ligand-to-metal ratio of 1:1 was selected for the RHF catalyst in FTS/RHF tandem reactions.
As full 1-octene conversion was achieved during previous experiments, the catalyst concentration in the reactor was lowered in subsequent experiments (Table S3, entries 3.5-3.7). Even upon lowering the catalyst loading from 1.5 mol% (Entry 3.1) to 0.19 mol% (Entry 3.7), full 1-octene conversion was achieved, alongside a significant increase in the Turnover Number (TON) from 63 to 389, showing that the RHF catalyst is much more active than observed during the initial experiments with higher catalyst concentrations.  Table S5: Investigation of product regioselectivity for Fischer-Tropsch synthesis (FTS)-derived and non-FTS tracer α-olefin educts in the tandem reaction FTS/RHF (reductive hydroformylation). The intrinsic reactivity of the molecular RHF catalyst has been assessed with 5-methyl-1-hexene as model olefin educt. The latter has been additionally applied as a non-FTS (branched backbone) α-olefin tracer olefin in tandem reactions. 1 Molar ratio of 1-pentanol to 2-methyl-1-pentanol for tests with 5-methyl-1-hexene as educt. 2 Molar ratio of 5-methyl-1-hexanol to 2,4-dimethyl-1-pentanol, both originating from the 5-methyl-1-hexene non-FTS tracer olefin. Reaction conditions: 473 K, P= 120 bar (at RT), H2:CO = 2, t = 24 h, FTS catalyst: NaPr-CoRu/AOmM; RHF catalyst: Co2CO8 + PCy3 (L:M = 1.0 (P/Co, at/at)), CoFTS:CoRHF = 170:70 for entry 5.5. The conversion of the model olefin educts was 84-100%. For tests with liquid olefin educt, hydrogenation product selectivity ≤ 7% in all cases. 3 The Co-free FTS support refers to NaPr/AOmM, i.e. a solid synthesized to have the composition of the FTS catalyst without the active CoRu metals, submitted to the same activation treatment, i.e. reduction in H2 flow. The set of experiments summarized in Table S6 was designed to assess whether endogenous α-olefins, i.e. those originating from the FTS conversion of syngas, and an exogenous tracer α-olefin (herein 5-methyl-1-hexene), which is not produced on the surface of the solid FTS catalyst, follow the same or different reductive hydroformylation pathways in the tandem FTS/RHF process. The alcohol product n:iso ratio was selected as a proxy for the RHF mechanism. Applied on the 5-methyl-1-hexene α-olefin as neat educt, the molecular RHF catalyst (Co2(CO)8+PCy3) led to an n:iso ratio in the resulting alcohol products of 3.1, indicating an intrinsic preference for an anti-Markovnikov reaction regioselectivity. This regioselectivity was maintained when the reaction was performed in the presence of the metal-free, therefore FTS-inactive, porous support material which is part of the composition of the FTS catalyst, suspended in the liquid reaction medium. In the tandem FTS/RHF syngas conversion process, alcohol products originating from the tracer non-FTS α-olefin showed an n:iso ratio of 2.3, slightly lower than for alcohols which could be produced as either primary FTS products or as a result of the RHF of FTS olefin intermediate products, which showed an n:iso ratio of 3.0. This difference in alcohol regio-selectivity can be explained in full by considering the contribution of strictly linear FTS primary products to the latter lump, therefore suggesting that both endogenous (desorbed from the FTS catalyst) α-olefin and the exogeneous tracer α-olefin compounds undergo a mechanistically similar RHF on the molecular catalyst. 0.60 a Hydrocarbon chain-growth probability. b linear-to-iso alcohol ratio c Alcohol chain-growth probability d H2:CO = 1.