The Hydrodeoxygenation of Glycerol over NiMoS_x: Catalyst Stability and Activity at Hydropyrolysis Conditions

Abstract

Catalytic activity tests were run to elucidate the chemistry and catalyst stability for the hydrodeoxygenation of glycerol and other aliphatic oxygenates over a NiMoSx/Al2O3 catalyst at different pretreatments at hydropyrolysis conditions in a continuous flow reactor. Reactivity metrics were developed to quantify and compare the reactivity of NiMo for deoxygenation, hydrogenation, and C−C cleavage. Activity experiments showed sulfided NiMo and reduced NiMo catalysts had similar deoxygenation and hydrogenation activity for glycerol HDO at 400 °C and 270 psig H2 with the NiMoSx catalyst showing higher C−C cleavage activity. Without a sulfur co‐feed, both the NiMoSx and NiMoOx catalysts lost >40 % deoxygenation activity over 30 h time on stream. With a 2100 ppm H2S co‐feed the NiMoSx catalyst showed a 12 times decrease in the deactivation rate for deoxygenation and 6 time decrease in the deactivation rate for hydrogenation. The main products at high conversion were propylene, propane, ethylene, methane, CO, methanol, ethanol, and 1‐propanol. At low conversion, the major products were unsaturated allyl alcohol, acrolein, hydroxyacetone, and acetaldehyde. With no H2S co‐feed at short contact times, there was a significant amount of carbon loss possibly due to condensation reactions, while at 2100 ppm H2S in the feed, the carbon balance was 102.4 %. Temperature programmed oxidation of the spent NiMoSx catalysts after 30 h of glycerol HDO without an H2S co‐feed showed that one of the causes of deactivation was coking.

Bioglycerol-to-Propylene Routes: From Fundamental Catalysis to Process Design and Marketing

“…The formation of hydroxyacetone and 1,2-propanediol intermediates during the GTP reaction formed over bifunctional sites and under a low temperature has been reported. , However, the proposed GTP pathway (Scheme b) is still incomplete because propionaldehyde and n -propanol can also establish an isomerization equilibrium with allyl-alcohol and i -propanol, respectively. ,, Thus, Sun et al have proposed a new GTP mechanism over metals/acid sites taking into account that partial C–O and C–C breaking to additional intermediates such as propionaldehyde, propionic acid, methanol, acetaldehyde, ethanol, ethylene-glycol, ethylene, propane and CO 2 have been included in the new pathway (Scheme S3). Some of the reported intermediates, whose formation becomes prominent under an H 2 atmosphere, has been experimentally confirmed. , …”

“…The species studied for GTP reactions are noble metals (e.g., Ir, ,,, Ru, ,,,,, Pt, ,,,,,, Pd, ,,,, Rh, , and Re,), functionalized systems based on non-noble transition metals (e.g., MoO x , ,− ,,− β-Mo 2 C, , η-MoC, NiMoS x , WO x , ,,, Ni, ,,,,,, Cr, ,,,, Fe, ,,,,,, Zn, ,,, V, ,,, Nb, ,, Cu, ,,,,,,,, ), nonmetals (e.g., Li, Ca, Mg, HBO 3 , I, P, , Br, and Carbon, ,…”

“…This step eventually breaks C–H and C–O bonds with a weaker barrier, forming double bonds; Mo=O on the catalyst surface and C=C in the 1,2- or 1,3-enols. These highly unstable enols OH quickly transit to their respective keto tautomers, , depending on whether the C–O cleavage is taking place from primary or secondary. Keto–enols are thus interconverted via adsorbed enolic −OH on a Mo vacancy (Scheme b).…”

“…Indeed, GTP routes is undergoing advances in research in terms of both fundamental catalysis and process design ,,− by exploring different transformation strategies from both heterogeneous and homogeneous catalysis. GTP routes are being investigated through high-temperature processes, ,,,,,, multisteps reactions, including triple-stage reactors, , separate double reactors, ,, tandem or dual-bed catalysts, ,,, and single-step conversion strategies. ,,,− ,,,,− These studies conclude that in the future GTP catalysis may become a sustainable bridging route between the biorefinery and polyolefin industries. Nonetheless, integrating GTP routes in a unified network, from biomass to sustainable propylene, raises intrinsic challenges, such as the nature of the most efficient GTP configurations, control of the interoperability of multisteps and/or combined bed reactors, influenced by contact states between catalyst beds, operating conditions, reaction mechanisms, and so forth.…”

A unified view on catalytic conversion of biomass and waste plastics

“…NiMo-sulfide and CoMo-sulfide have received increasing interest in the past five decades owing to their high hydrogenation activity as well as their cheaper costs than noble metals. However, they require co-feeding of a sulfur source (for example, H 2 S) because of the rapid deactivation of the metals from loss of the active metal-sulfide moieties as well as coke deposition 52 , 53 . For the zeolite component, 12-membered ring zeolites (USY, Beta) are ideal to produce diesel or jet fuel, whereas the narrow pore structure of ZSM-5 limits diffusion of branched hydrocarbons, inducing overcracking 54 .…”