Atomic Layer Deposition with TiO₂ for Enhanced Reactivity and Stability of Aromatic Hydrogenation Catalysts

Abstract

Hydrogenation of aromatic molecules in fossil- and bio-derived fuels is essential for decreasing emissions of harmful combustion products and addressing growing concerns around urban air pollution. In this work, we used atomic layer deposition to significantly enhance the hydrogenation performance of a conventional supported Pd catalyst by applying an ultrathin coating of TiO2 in a scalable powder coating process. The TiO2-coated catalyst showed substantial gains in the conversion of multiple aromatic molecules, including a 5-fold improvement in turnover frequency versus the uncoated catalyst in the hydrogenation of naphthalene. This activity enhancement was maintained upon scaling the coating synthesis process from 3 to 100 g. Based on the results from X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and computational modeling, the activity enhancement was attributed to ensemble effects resulting from partial TiO2 coverage of the Pd surface rather than fundamental changes to the Pd electronic structure. Additional durability testing confirmed that the TiO2 coating improved the thermal and hydrothermal stability of the catalyst as well as tolerance toward sulfur impurities in the reactant stream. Using an economic model of an industrial deep hydrogenation process, we found that an increase in catalyst activity or lifetime of 2× would justify even a relatively high estimate for the cost of TiO2 atomic layer deposition coatings at scale.

Selective Hydrogenation of Naphthalene to Decalin Over Surface‐Engineered α‐MoC Based on Synergy between Pd Doping and Mo Vacancy Generation

“…The hydrogenation saturation of aromatic hydrocarbons is a key industrial process, [ 1–4 ] as transportation fuels with higher contents of aromatic hydrocarbons not only show worse combustion performance but also generate exhaust gases with more harmful products (e.g., polycyclic aromatic hydrocarbons and particulate matter). [ 4,5 ] Moreover, the excessive content of aromatic hydrocarbons in jet fuels can cause elastomer seal swelling. [ 6 ] Recently, the catalytic hydrogenation of aromatic hydrocarbons has become increasingly important for the green synthesis of bio‐based platform chemicals, as exemplified by the production of cyclohexanone (key intermediate in nylon production) by the hydrogenation of bio‐derived phenol.…”

“…[9] Notably, the latter product is much more difficult to obtain than the former because of the reversibility of the consecutive reaction and the difficulty of dearomatizing the stable aromatic ring in tetralin. [5,10] Decalin is a high-added-value organic solvent with a strong ability to dissolve ultrahigh-molecular-weight polyethylene at low temperatures and is widely used as a fuel, raw material for nylon and softener production, hydrogen storage medium, etc. [11] Currently, the cost of decalin production remains high, which makes the selective hydrogenation of NAP to decalin a promising process.…”

Engineering Heterogeneous Catalysis with Strong Metal–Support Interactions: Characterization, Theory and Manipulation

“…Recently, McNeary et al synthesized Pt/TiO 2 catalysts with SMSI state using ALD at 150 °C with titanium isopropoxide and water as the precursors. [109] The TiO 2coated catalyst showed substantial gain in converting multiple aromatic molecules, including a 5-fold improvement in turnover frequency versus the uncoated catalyst in the hydrogenation of naphthalene. The improved activity was attributed to ensemble effects resulting from partial blockage of the Pd surface by the TiO 2 layer.…”

N-Doped Carbon Interior-Modified Mesoporous Silica-Confined Nickel Nanoclusters for Stereoselective Hydrogenation

“…The demand for diesel worldwide in recent years has reached its highest level among petroleum products (27 million barrels per day in 2020), according to the World Energy Agency (IEA). Owing to the intensified scarcity of oil resources and deterioration of quality, the proportion of diesel from heavy oil fluid catalytic cracking (FCC) is increasing, which contains a great deal of polycyclic aromatic hydrocarbons (PAHs more than 70%). , However, these PAHs not only significantly reduce the cetane number of diesel but also wreak havoc on human health, environment, and engines’ life. − As a result, many countries have enacted strict regulations to confine the PAH content in diesel (less than 7% in the Europe IV standard) …”

“…The hydrogenation of naphthalene is a reversible parallel–consecutive reaction giving tetralin and decalin (cis- and trans-isomers) . Notably, it is rather difficult to obtain pure decalin because of the stable aromatic ring in tetralin. , With the excellent solubility, volatility, and bicyclic alicyclic hydrocarbon structure, decalin is widely used as a raw material for drug intermediates, nylon production, and hydrogen storage. ,, In addition, trans-decalin possesses superior thermodynamic stability and optoelectronic property than cis-decalin, which makes the stereoselective hydrogenation of naphthalene to trans-decalin a promising process…”