Low Hydrogen Pressure Research Articles

Low-pressure CO2 hydrogenation coupled with toluene methylation to para-xylene using atomic Pd-doped ZnZrOx–HZSM-5

Selective methylation of aromatics using CO2/H2 presents a promising avenue for producing high-value-added chemicals with high selectivity. Herein, we introduced atomically dispersed Pd species into ZnZrOx solid solution and combined with HZSM-5 to create a bifunctional catalyst, applying to selectively synthesize para-xylene through toluene methylation using CO2/H2 at low pressure. Remarkably, 0.1 wt% Pd in PdZnZrOx–HZSM-5 afforded the selectivity of xylene in CO-free products and para-xylene in xylene to 90.0% and 85.6% at 0.5 MPa, respectively. Spectroscopic characterizations revealed that atomically dispersed Pd species enhance the dissociation of adsorbed hydrogen and facilitate the creation of oxygen vacancies, benefiting the CO2 hydrogenation to CHxO intermediates. Density functional theory calculations suggested that Pd-doped ZnZrOx reduces the energy barrier for hydrogenating H2COOH* to H2CO*, aiding to form CH3O* intermediate for toluene methylation. This work provides insights into the design of catalysts for the selective methylation of aromatics using CO2/H2 at low pressure.

Molecular transformation of heavy oil during slurry phase hydrocracking process: influences of operational conditions

The influences of reaction temperature, duration, pressure, and catalyst concentration on the molecular transformation of residual slurry phase hydrocracking process were investigated. The molecular composition of the heteroatom compounds in the residue feedstock and its upgrading products were characterized using high-resolution Orbitrap mass spectrometry coupled with multiple ionization methods. The simultaneous promotion of cracking and hydrogenation reactions was observed with increasing of the reaction temperature and time. Specifically, there was a significant increase in the cracking degree of alkyl side chain, while the removal of low-condensation sulfur compounds such as sulfides and benzothiophenes was enhanced. In particular, the cracking reactions were more significantly facilitated by high temperatures, while an appropriately extended reaction time can result in the complete elimination of the aforementioned sulfur compounds with a lower degree of condensation. Under conditions of low hydrogen pressure and catalyst concentration, the products still exhibit a high relative abundance of easily convertible compounds such as sulfoxides, indicating a significant deficiency in the effectiveness of hydrogenation. The hydrogen pressure exhibits an optimal value, beyond which further increments have no effect on the composition and performance of the liquid product but can increase the yield of the liquid product. At significantly high catalyst concentration, the effect of desulfurization and deoxidation slightly diminishes, while the aromatic saturation of highly condensed compounds was notably enhanced. This hydrogenation saturation effect cannot be attained through manipulation of other operational parameters, thereby potentially benefiting subsequent product processing and utilization. This present study demonstrates a profound comprehension of the molecular-level residue slurry phase hydrocracking process, offering not only specific guide for process design and optimization but also valuable fundamental data for constructing reaction models at the molecular level.

In-situ preparation of MnFeCoNiCu/C for the sustainable co-production of bio-jet fuel and green diesel under solvent-free and low hydrogen pressure conditions

The conversion of non-edible oils such as fatty acid methyl esters (FAME) into green and renewable liquid fuels align with the current trend of sustainable development. However, traditional processes often involve multi-step process to prepare catalyst and require high-pressure hydrogen. This study reports a strategy for the in-situ preparation of MnFeCoNiCu/C catalyst, enabling the one-step conversion of FAME into bio-jet fuels and hydrocarbon-based diesel under solvent-free and low-pressure conditions. The effect of active metal loading, reaction temperature, hydrogen pressure, and ZSM-5 zeolite addition on the catalytic performance was investigated. Under the conditions of reaction temperature 350 ℃ and hydrogen pressure 2 MPa, the conversion rate of FAME reaches 100 %, and the selectivity of bio-jet fuel and green diesel is 48.35 % and 51.05 %, respectively. A small number of olefins, cycloalkanes, and aromatics can also be detected in the products. After the 4 cycles of AC-15 catalyst, the selectivity of bio-jet fuel and diesel are 40.09 % and 39.81 %, respectively. The above research work provides a mild and efficient method for the preparation of renewable bio-jet fuel and green diesel.

MIL-101(Cr) supported Pt and Au-Pt composites as active catalysts for the selective hydrogenation of nitrobenzene under mild reaction conditions

In this study, we report the successful synthesis of monometallic Pt(2 wt.%)/MIL-101(Cr) and bimetallic Au(1 wt.%)-Pt(1 wt.%)/MIL-101(Cr) catalysts with low dimension MeNPs by the double-solvent (DS) method. The catalysts were characterized by powder X-ray diffraction (PXRD), N2 sorption analysis (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM). The characterization results demonstrated the presence of well-dispersed Pt and Au-Pt nanoparticles (2.9 and 2.7 nm, respectively), located mainly inside the pores of MIL-101(Cr). The stronger interaction of Au-Pt NPs with the support compared to Pt NPs was demonstrated by H2-TPR and XPS, which proved the existence of charge exchange between Pt NPs and Cr from MIL-101 in the case of Au(1 wt%)-Pt(1 wt%)/MIL-101(Cr), but not in the case of Pt(2 wt%)/MIL-101(Cr). The composite materials were tested in the catalytic selective hydrogenation of nitrobenzene to aniline in liquid phase under mild conditions (low temperature, low hydrogen pressure), and in the presence of a biomass-derived non-toxic solvent (ethanol). The bimetallic Au(1 wt%)-Pt(1 wt%)/MIL-101(Cr) catalyst showed superior catalytic activity as compared to the monometallic Pt(2 wt%)/MIL-101(Cr) catalyst. This is due to the synergetic effect between the two metals as demonstrated by the projected density of states studies.

Pivotal MoOx-decorated Ru/C with a monomeric structure boosts the room temperature and low-pressure hydrogenation of levulinic acid to γ−valerolactone

Pivotal molybdenum oxide-decorated ruthenium on charcoal catalysts exhibited high efficiency and selectivity for the room temperature and low pressure hydrogenation of levulinic acid (LA) to renewable fuel γ−valerolactone (GVL). The Ru-(y)MoOx/C (y = the amount of co-loaded Mo in wt%) catalysts were synthesised by using a one-pot coprecipitation-hydrothermal method of a solution that consisted of Ru and Mo species at 150 °C for 24 h, followed by reduction with H2 at 300–600 °C for 1.5 h. The Ru-(0.55)/MoOx/C catalyst (pre-reduced at 500 °C) exhibited high dispersion of Ru nanoparticles on the surface of MoOx/C composite support, demonstrating the highest yield of GVL (>99) with a turnover frequency (TOF) reaching up to 2730 h−1 at 30 °C, 10 bar H2, and 1 h. The Ru-(0.55)/MoOx/C also catalysed various carboxylic acids to corresponding alcohols and was reusable without any significant loss of selectivity.

Hydrogenation features of TiZrHfNbTa high-entropy alloy produced by calcium-hydride synthesis

A high-entropy alloy TiZrHfNbTa has been synthesized by a method of the mutual reduction of the higher oxides of corresponding metals with calcium hydride. The alloy structure was characterized and hydrogen absorption properties were studied. The alloy of overall equiatomic composition TiZrHfNbTa consists of two BCC phases with unit cell parameters of 3.419 and 3.328 Å. The distribution of the elements was established as follows: Ti0.21Zr0.24Hf0.24Nb0.25Ta0.06 (BCC-I) and Ti0.15Zr0.05Hf0.10Nb0.08Ta0.62 (BCC-II). The hydrogenation behavior of the alloy under different conditions was thoroughly studied. It was shown that complete hydrogenation resulted in the formation of FCC-type (H/M → 2) and BCT-type hydrides (H/M → 1) from BCC-I and BCC-II, respectively. Under low hydrogen pressure (< 212.8 Torr), BCC-I absorbed up to 0.33 at. H/M within a solid solution without changing the structural type. According the kinetic analysis, this process can be described as a second order reaction with activation energy of 102 kJ/mol. The BCC-I-based solid solution is capable of retaining hydrogen in a deep vacuum at a temperature of 430 °C. The fast kinetics of hydrogen absorption and high thermal stability allow us to suggest the studied two-phase TiZrHfNbTa alloy as a promising getter for vacuum devices.

High cyclic stability and low plateau of Ti2V2Zr/NaH/Al hydrogen storage composite system prepared by ultrasound-assisted ball milling

NaH/Al doped with Ti2V2Zr with the aim of lowering the rehydrogenation pressure, lowering the dehydrogenation temperature, and improving the hydrogenation/dehydrogenation kinetics of NaAlH4. It was found that moderate ultrasonic-assisted wet grinding was beneficial to fine particles efficiently, improved uniformity of particle size, and reduced lattice distortion because its crystalline phase can converge more active hydrogen atoms and reduce the energy barrier of H exchange between the alloy and the matrix, thus improving the comprehensive hydrogen storage performance of the composite systems. It could reversibly store 4.81 wt% of hydrogen and completely hydrogenation under a low hydrogen pressure of 55 atm, its starting and ending dehydrogenation temperatures decrease by 81 and 89 °C, respectively, and the activation energies of the two-step dehydrogenation decrease by 26.7 and 52.7 kJ mol−1 respectively, with a dehydrogenation capacity retention of up to 99.58% over five cycles.

EFFECT OF AN ALKYL SUBSTITUTE ON HYDROCONVERSION OF INDIVIDUAL AROMATIC HYDROCARBONS ON Co/HZSM-5/SO42-–ZrO2 COMPOSITE CATALYST

A systematic study of the hydrogenation of individual aromatic hydrocarbons (benzene, toluene, xylene) and their mixtures was carried out at 1800C, H2/Ar=7, WHSV = 2h-1 and atmospheric pressure on a composite catalyst 0.4%Co/HZSM-5/SO42-(2.0%)–ZrO2. It has been established that the developed catalyst has a high hydrogenating ability with respect to aromatic hydrocarbons at low hydrogen pressures. Alkyl-substituted benzenes turned out to be more active. It was found that alkyl substituents increase the activity of hydrogenation of the benzene ring of an aromatic hydrocarbon. According to their conversion, benzene, toluene and xylene form the following sequence: benzene&lt;toluene&lt;xylene. It was found that the optimal temperature for the process of hydroconversion of aromatic hydrocarbons on a composite catalyst is 1800C. The influence of the concentration of the hydrogenating component of the catalyst – Co on the hydroconversion was also investigated. It was found that the optimal concentration of Co is 0.4wt %. It has been established that in a benzene:toluene:xylene mixture, the conversion of benzene in comparison with its separate hydroconversion increases by more than 10%. The hydroconversion of aromatic hydrocarbons is accompanied by the formation of high-octane naphthenic hydrocarbons - cyclohexane, methylcyclohexane and methylcyclopentane. The antibatic change in the yield of CH and MCP with the duration of the experiment shows that the hydrogenation of the aromatic ring is primary and the isomerization of C6H10 to MCP is secondary, i.e. MCP is the result of a sequential transformation. The absence of dimethylcyclohexane (DMCH) in the benzene:toluene:xylene mixture conversion products suggests that the benzene and xylene conversions additionally involve transalkylation

Additively Manufactured Silicone Polymer Composite with High Hydrogen Getter Content and Hydrogen Absorption Capacity.

Hydrogen getters consisting of 1,4-bis[phenylethynyl] benzene (DEB) and a carbon-supported palladium catalyst (Pd/C) have been used to mitigate the accumulation of unwanted hydrogen gas in a sealed system. Here, we report the formulation of a composite resin consisting of silicone polymer plus DEB-Pd/C as an active getter material and the additive manufacturing of silicone getter composites with a high getter content (up to 50 wt %). NMR and DSC studies suggest no reaction between the silicone polymer resin and DEB even at elevated curing temperatures (75 °C). Getter composites with varying amounts of getter and filler were formulated, and their rheological properties were studied. The two composite resins with good printability parameters and different getter contents were chosen to make 3D-printed samples. The hydrogen absorption capacity of these samples was studied at a low hydrogen pressure of 750 mTorr of pure hydrogen. The getter composite with 50 wt% of getter showed normalized DEB conversion of 83%, with the hydrogen adsorption capacity of 100.2 mL of H2 per gram of polymer getter composite.

Hydrogen adsorption and diffusion behavior in kaolinite slit for underground hydrogen storage: A hybrid GCMC-MD simulation study

Underground hydrogen storage (UHS) in reservoirs offers the opportunity for large-scale and long-term storage of hydrogen. In order to understand the fundamental mechanisms of hydrogen storage and transportation, it is crucial to study the adsorption and diffusion behavior of hydrogen in reservoirs. By utilizing a hybrid GCMC and MD simulation procedure, we investigated the adsorption and diffusion behavior of hydrogen in kaolinite slit with pore sizes ranging from 1 to 20 nm at pressures up to 30 MPa and temperatures ranging from 303 to 423 K. Hydrogen distribution, excess adsorption, diffusion coefficient, and gas–solid interaction energy were analyzed in relation to pore size, temperature, pressure, and mineralogy. When pores are larger than 5 nm, most of the hydrogen is located in the bulk phase, resulting in insignificant hydrogen loss due to adsorption. Therefore, reservoirs with pores larger than 5 nm are suitable for UHS. Reservoirs with low temperatures and high hydrogen pressures are conducive to UHS, but the hydrogen mobility is reduced. The mineralogy of the formation results in pore surfaces with different charge properties, which significantly affects hydrogen storage. Although van der Waals interaction dominates the gas–solid interaction, Coulomb interaction remains important. The negatively charged pore surface mitigates the gas–solid Coulomb interaction, thereby preventing hydrogen loss through adsorption. This study enhances our understanding of hydrogen storage mechanisms in subsurface porous media and elucidates the influence of various factors. Consequently, it provides a theoretical framework for selecting UHS sites.

Highly efficient and direct recovery of low-pressure hydrogen isotopes from tritium extraction gas by PdY alloy membrane permeator

Low-pressure hydrogen recovery is crucial for the fusion reactor deuterium-tritium fuel cycle, and the usual treatment is achieved through multiple steps of enrichment and separation, which has the drawbacks of complex processes and high energy consumption. In this work, a membrane permeator including 12 sets of Pd92Y8 at% alloy tubes has been investigated for the permeability and extraction of hydrogen in low-pressure mixtures. The hydrogen permeation through dense Pd-based membrane mechanism and corresponding Sieverts’ exponents have been verified. The concentration polarization effect is deducted from the results. Through pure hydrogen permeation test, the cold-rolling 80 μm thick Pd92Y8 at% membrane has hydrogen permeability at 400 °C of 3.43×10−8 mol∙m−1∙s−1∙Pa−0.5, which is higher than that of PdAg alloy membrane under the same conditions. Highly efficient recovery efficiency has been achieved for low hydrogen pressure mixtures, and the PdY alloy membrane permeator with 678 cm2 effective area could reach around 95% hydrogen extraction recovery for 0.1 mol% hydrogen-helium mixture and 97.74% recovery for 0.33 mol% at the rate of 21 standard liter per minute (SLM). It indicates that the PdY alloy membrane permeation can be an alternative solution for efficiently recovering low-pressure hydrogen isotopes in tritium extraction gas.

Effect of Hydrogen Pressure and Punch Velocity on the Hydrogen Embrittlement Susceptibility of Pipeline Steels Using Small Punch Tests under Gaseous Hydrogen Environments at Room Temperature

The in situ small punch (SP) test method is a simple screening technology developed to assess the hydrogen embrittlement (HE) characteristics of structural steels. This method can easily adjust the influencing parameters such as test temperature, gas pressure, and punch velocity depending on the hydrogen service environment. With increased hydrogen consumption, using pipelines for mass hydrogen transportation is being considered. This study evaluated the HE susceptibility of API-X52 and API-X70 steels, considering the hydrogen usage environment. The study investigated the effects of hydrogen pressure and punch velocity on the HE behaviors of each pipe steel at room temperature using the SP energy and relative reduction in thickness (RRT) to determine their effect on HE susceptibility quantitatively. The study found that hydrogen pressure produced a different HE effect; the lower the hydrogen pressure, the more HE was relieved. Particularly, when the punch velocity was high, such as 1 mm/min, the HE effect was significantly relaxed. However, when the punch velocity was below 0.01 mm/min, HE occurred even at low hydrogen pressure conditions, meaning hydrogen diffusion within the specimen during the SP testing reached a critical hydrogen concentration to create a brittle fracture. Both pipeline steels showed similar HE behaviors under a wide range of H2 pressures and punch velocities, showing an inverse S-curve for quantitative factors of SP energy and RRT against the H2 pressure at 1.0 mm/min punch velocity. The study classified the observed HE behaviors into four types based on quantitative and qualitative aspects. These findings confirm that the in situ SP test is a useful screening technique, and the factor RRT can be effectively applied to the HE screening of pipeline steels in low and high-pressure hydrogen environments.

Metal-Acid Interface Engineering in Pd-WOx Bifunctional Catalysts for the Hydroalkylation Tandem Reaction of Benzene.

The hydroalkylation tandem reaction of benzene to cyclohexylbenzene (CHB) provides an atom economy route for conversion and utilization of benzene; yet, it presents significant challenges in activity and selectivity control. In this work, we report a metal-support synergistic catalyst prepared via calcination of W-precursor-containing montmorillonite (MMT) followed by Pd loading (denoted as Pd-mWOx/MMT, m = 5, 15, and 25 wt %), which shows excellent catalytic performance for hydroalkylation of benzene. A combination study (X-ray diffraction (XRD), hydrogen-temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis, Raman, and density functional theory (DFT) calculations) confirms the formation of interfacial sites Pd-(WOx)-H, whose concentration is dependent on the interaction between Pd and WOx. The optimized catalyst (Pd-15WOx/MMT) exhibits a CHB yield of up to 45.1% under a relatively low hydrogen pressure, which stands at the highest level among state-of-the-art catalysts. Investigations on the structure-property correlation based on in situ FT-IR and control experiments further verify that the Pd-(WOx)-H structure serves as the dual-active site: the interfacial Pd site accelerates benzene hydrogenation to cyclohexene (CHE), while the interfacial Bronsted (B) acid site in Pd-(WOx)-H boosts the alkylation of benzene and CHE to CHB. This study offers a new strategy for the design and preparation of metal-acid bifunctional catalysts, which shows potential application in the hydroalkylation reaction of benzene.

Robust Co3O4 nanocatalysts supported on biomass-derived porous N-doped carbon toward low-pressure hydrogenation of furfural

Robust Co3O4 nanocatalysts supported on biomass-derived porous N-doped carbon toward low-pressure hydrogenation of furfural

Numerical analysis on the effect of diluted hydrogen fuel by a fixed amount of supplied hydrogen using a quasi-three-dimensional solid oxide fuel cell model

Solid oxide fuel cell (SOFC) has excellent fuel flexibility for various fuels. Despite some drawbacks like storage and transportation, hydrogen stands up as the best fuel for SOFC. Hydrogen fuel is diluted non-reactive gas species before it is supplied to the SOFC. In this study, a quasi-three-dimensional SOFC model with real microstructure is used to analyse the effect of the diluted fuel mixture. The hydrogen fuel is diluted with nitrogen and a small amount of steam. The mole amount of hydrogen within fuel mixtures is kept constant. On the other hand, the air that is supplied to the air channel of the SOFC remains unchanged. It is found that the cell that is supplied with the highest concentration of hydrogen has the highest performance due to its high partial pressure of hydrogen within the fuel mixture. Such a high partial pressure promotes a low anode concentration loss. Also, the cell that is supplied with a low hydrogen concentration is unable to benefit from its high average cell temperature as its performance is drained by the low partial pressure of hydrogen within the fuel mixture.

Interplay between Catalyst Complexes and Dormant States: In Situ Spectroscopic Investigations on a Catalyst System for Alkene Hydroformylation

Results from a detailed in situ IR and NMR spectroscopic study on a monophosphite-modified rhodium catalyst system are presented. Equilibria that occur between the catalytically active hydrido rhodium(I) complexes and formally inactive dinuclear rhodium(0) complexes as well as mononuclear ortho-metalated rhodium(I) complexes have been investigated. The latter can be considered as “dormant states”, which are formed at conditions with lower hydrogen pressures or [H2]/[Rh] ratios. It was found that dimer formation is dominant at lower temperatures and higher rhodium concentrations, whereas ligand metalation is effective at higher temperatures. At the appropriate partial pressure of hydrogen, the regeneration of hydrido rhodium(I) complexes takes place on a short time scale from both states. Especially, the temporary stabilization of the catalyst via ligand metalation during a catalyst recycling procedure represents a feasible approach.

Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy

TiFe alloy can store hydrogen at room temperature and low hydrogen pressure, and its theoretical hydrogen storage capacity is up to 1.8 wt%. However, TiFe alloy needs to be activated at high pressure (5 MPa hydrogen) and high temperature (673–723 K), which limits the practical application of TiFe alloy. The as-cast Ti 21.7 Y 0.3 Fe 16 Mn 3 Cr alloy was milled for 0, 0.5, 0.75, 1, and 3 h to study the effects of ball milling on phase structures and hydrogen storage performances. Emphasis was focused on the activation process of as-milled alloys at different temperatures, including the activation process at 483, 443, and 403 K. The results show that the alloys were consisted of TiFe phase, and [Fe, Cr] solid solution. The nanocrystalline boundary produced by milling and the phase boundary provided by the second phase provide a large number of channels for hydrogen diffusion and promote the improvement of hydrogen storage performances. The time required for activation process of as-milled alloys was significantly reduced, and the activation time of as-milled (0.75 h) was only 4 min, and its enthalpy variation for hydrogen absorption and desorption was 22.943 and 26.215 kJ mol −1 H 2 , respectively. • The phase composition and micro-structure of the milled Ti 21.7 Y 0.3 Fe 16 Mn 3 Cr alloy were studied. • Nanocrystalline boundary produced by milling provides many channels for hydrogen diffusion. • Ball milling improves the activation process of the alloy and shortens the activation time. • The optimum milling time of the alloy is 45 min, and its activation time is shortened to 4 min.

Low hydrogen pressure effect over microhardness and impact toughness of an experimental X-120 microalloyed steel

In the present work, the susceptibility to hydrogen embrittlement under hydrogen pressure was evaluated for an experimental X-120 microalloyed steel with four quenching treatments to determine the effect of hydrogen on the hardness and toughness behaviour, for its use in gas and oil transport. The steel was reheated at 820° and 900 °C and then quenched in four different cooling media. The microstructure obtained by quenching in spray water showed a martensite-bainite type microstructure, and the pressurized air condition showed a microstructure composed of bainite and acicular ferrite. In contrast, a microstructure composed mainly of finer lath martensite-bainite and acicular ferrite was obtained in the water-oil emulsion. In the oil quenching condition, a microstructure consisting of banded martensite, polygonal ferrite, and acicular ferrite was obtained. Susceptibility to hydrogen embrittlement was determined by hydrogen gas pressure testing at 1, 4, and 7 MPa. The results showed a clear trend where the steel decreases its impact toughness due to the effect of hydrogen pressure, with a maximum decrease of 29%, 24%, and 39%, respectively, for each hydrogen pressure condition (1, 4, 7 MPa).

Recent advances on catalysts for photocatalytic selective hydrogenation of nitrobenzene to aniline.

Selective hydrogenation of nitrobenzene (SHN) is an important approach to synthesize aniline, an essential intermediate with extremely high research significance and value in the fields of textiles, pharmaceuticals and dyes. SHN reaction requires high temperature and high hydrogen pressure via the conventional thermal-driven catalytic process. On the contrary, photocatalysis provides an avenue to achieve high nitrobenzene conversion and high selectivity towards aniline at room temperature and low hydrogen pressure, which is in line with the sustainable development strategies. Designing efficient photocatalysts is a crucial step in SHN. Up to now, several photocatalysts have been explored for photocatalytic SHN, such as TiO2, CdS, Cu/graphene and Eosin Y. In this review, we divide the photocatalysts into three categories based on the characteristics of the light harvesting units, including semiconductors, plasmonic metal-based catalysts and dyes. The recent progress of the three categories of photocatalysts is summarized, the challenges and opportunities are pointed out and the future development prospects are described. It aims to give a clear picture to the catalysis community and stimulate more efforts in this research area.

Understanding hydrogen pressure control of furfural hydrogenation selectivity on a Pd(1 1 1) model catalyst

We investigate the postulate that hydrogen pressure influences the furfural hydrogenation selectivity on palladium to form decarbonylation products at low hydrogen pressures, but 2-methyl furan at higher pressures. This change is caused by co-adsorbed hydrogen changing the orientation of adsorbed furfural; low hydrogen coverages favor flat-lying furfural, higher coverages form tilted species. This was tested for hydrogenation of furfural on a Pd(111) single crystal. The product distribution agreed with the postulate, with 100% selectivity to furan and tetrahydrofuran for low hydrogen pressures, with 2-methyl furan increasing with hydrogen pressure. The origin of the effect is explored using reflection–absorption infrared spectroscopy. This showed that co-adsorbed hydrogen influenced the orientation in a way predicted by theory. It was also found that other co-adsorbates displayed similar effects implying that a range of molecules in the reaction mixture could have significant effects on the furfural selectivity.