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Palladium metal has been used extensively in the hydrogenation reactions due to their great affinity towards hydrogen atoms. In the present study, the catalyst preparation attempted with Pd supported Hollow Ceramic Microspheres using wet impregnation method and its use as catalysts is explored in the hydrogenation of 2-ethylanthraquinone studing the effect of the reaction time, temperature, volume of working solution and the catalyst dosages on the conversion of 2-ethylanthraquinone and yield of hydrogen peroxide. The hydrogenation reaction of 2-ethylanthraquinone is the key step in the anthraquinone method for the industrial production of the hydrogen peroxide. The Pd supported catalyst was characterized by XRF, FTIR, and BET to confirm the composition of the prepared catalyst, Pd deposition, and the surface area. The highest catalyst activity was found to be 9.42 ​g/L with the maximum conversion of 96% at 70°C, 0.3 ​MPa. The kinetics of the heterogeneous hydrogenation reaction of 2-ethylanthraquinone with Pd supported on Hollow Ceramic Microspheres as catalyst was also investigated. This paper is in contribution of our earlier publication.

A series of χ wt % Pd-(1-χ) wt % Ir (χ = 0.75, 0.50, and 0.25) catalysts supported on γ-Al2O3 have been prepared by co-impregnation and calcination-reduction, and subsequently employed in the hydrogenation of 2-ethylanthraquinone—a key step in the manufacture of hydrogen peroxide. Detailed studies showed that the size and structure of the bimetallic Pd–Ir particles vary as a function of Pd/Ir ratio. By virtue of its small metal particle size and the strong interaction between Pd and Ir, the 0.75 wt % Pd–0.25 wt % Ir/Al2O3 catalyst afforded the highest yield of H2O2, some 25.4% higher than that obtained with the monometallic 1 wt % Pd catalyst. Moreover, the concentration of the undesired byproduct 2-ethyl-5,6,7,8-tetrahydroanthraquinone (H4eAQ) formed using the Pd–Ir bimetallic catalysts was much lower than that observed with the pure Pd catalyst, which can be assigned to the geometric and electronic effects caused by the introduction of Ir. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3955–3965, 2017

The hydrogenation of 2-ethylanthraquinone (eAQ), 2-tert-amylanthraquinone (taAQ) and their mixtures with molar ratios of 1:1 and 1:2 to the corresponding hydroquinones (eAQH2 and taAQH2) were studied over a Pd/Al2O3 catalyst in a semi-batch slurry reactor at 60 °C and at 0.3 MPa. Compared to eAQ, TaAQ exhibited a significantly slower hydrogenation rate (about half) but had a higher maximum yield of H2O2 and a smaller amount of degradation products. This can be ascribed to the longer and branched side chain in taAQ, which limits its accessibility to the Pd surface and its diffusion through the pores of the catalyst. Density functional theory calculations showed that it is more difficult for taAQ to adsorb onto a Pd (111) surface than for eAQ. The hydrogenation of the eAQ/taAQ mixtures had the slowest rates, lowest H2O2 yields and the highest amounts of degradation products.

A series of bimetallic PdRu catalysts supported on γ-Al2O3 were prepared by incipient wetness impregnation method and were assessed in the 2-ethylanthraquinone hydrogenation process. It is found that the addition of Ru to Pd can improve the catalyst's activity and maintain high selectivity at the same time for 2-ethylanthraquinone hydrogenation. Several analysis techniques including N2 adsorption–desorption, ICP-AES, XRD, TEM, H2-TPR, H2-TPD and XPS were adopted for characterizing the structural and electronic properties of the samples. It is revealed that PdRu bimetallic system shows stronger hydrogen desorption behavior in contrast to the monometallic catalysts. In addition, the higher fraction of Pd2+ and the presence of Ru4+ in the PdRu system may act as the electrophilic sites for the adsorption and activation of the CO of the 2-ethylanthraquinone molecule through the lone electron pair of the oxygen atom. These factors may be attributed to the superior performance of PdRu bimetallic samples for 2-ethylanthraquinone hydrogenation.

Pd/oxide/cordierite monolithic catalysts (oxide = Al 2 O 3 , SiO 2 and SiO 2 Al 2 O 3 ) were prepared by the impregnation method. The results of ICP, XRD, SEM–EDX, XPS and N 2 adsorption–desorption measurements revealed that the Pd penetration depth increased with increasing the thickness of oxide layer, and the catalysts with Al 2 O 3 layers had the larger pore size than those with SiO 2 and SiO 2 Al 2 O 3 layers. Catalytic hydrogenation of 2-ethyl-anthraquinone (eAQ), a key step of the H 2 O 2 production by the anthraquinone process, over the various monolithic catalysts (60 °C, atmosphere pressure) showed that the monolithic catalyst with the moderate thickness of Al 2 O 3 layer (about 6 μm) exhibited the highest conversion of eAQ (99.1%) and hydrogenation efficiency (10.0 g·L − 1 ). This could be ascribed to the suitable Pd penetration depth and the larger pore size, which provides a balance between the distribution of Pd and accessibility of active sites by the reactants.

Highly dispersed Pd/AlPO-5 catalyst was prepared and tested in the hydrogenation of 2-ethylanthraquinone. Characterization results suggested that the abundant surface P-OH groups of AlPO-5 zeolite substituted NH3 ligands of [Pd(NH3)4]2+ precursor to form [Pd(NH3)3(POH)]2+. After calcination, the latter formed Pd-O-P interfacial linkage between Pd nanoparticles and AlPO-5, benefiting the suppression of Pd sintering. SiO2 and SiO2-AlPO-5 composite were used as supports for comparison. Catalyst supported on SiO2-AlPO-5 composite (25 wt% AlPO-5) exhibited improved catalytic activity and stability in consideration of reactant activation as well as the mass transfer of reactant molecules, which is expected to decrease precious metal loading in industrial application.

This paper reports an investigation on the degradation of cellulose via electro-Fenton method. The electrodes chosen were graphite/PTFE electrodes modified by 2-ethylanthraquinone (EAQ). The presence of EAQ greatly improved the rate of hydrogen peroxide formation on air-fed graphite/PTFE electrodes, which was determined by a UV spectroscopic method using molybdate as the color agent. Hydrogen peroxide can react with Fe 2+ to form hydroxyl radicals in an acidic medium, which accelerates cellulose degradation by cleaving the glycosidic bonds between glucose units. The degradation products of the cellulose contain soluble sugar and 5-HMF, which were fully characterized by 1 H NMR and 13 C NMR.

Present research concentrates on the role of alkali modifiers (Li, Na, K, Cs) in activity of 2%Pd/Al2O3 catalyst for 2-ethyl-9,10-anthraquinone (eAQ) hydrogenation. The catalysts with various content of alkali modifier (Me/Pd molar ratio ranges from 0.5 up to 4, Me-alkali metal) were prepared by impregnation of pre-reduced 2%Pd/Al2O3 catalyst with appropriate alkali metal carbonates. The XPS, EDS and TEM measurements show that alkali promoters are introduced into alumina matrix. The microcalorimertic experiments of CO adsorption prove the interaction of CO with catalysts leading to stronger bonding of carbon monoxide by alkali doped catalysts. The presence of alkali promoters in Pd/Al2O3 catalyst plays an essential role in the whole eAQ hydrogenation process. The nature of alkali promoter and its content (Me/Pd atomic ratio) in catalyst are of importance. As the alkalinity of promoter increases going from Li to Cs all the effects caused by their presence become stronger. In the presence of alkali doped catalysts the content of 2-ethyloxoanthrone (OXO, isomer of 2-ethyl-9,10-anthrahydroquinone) formed is higher than that on un-doped 2%Pd/Al2O3. On the other hand, reactions in the “deep hydrogenation” stage comprising the formation of 2-ethyl-5,6,7,8-tetrahydro-9,10-anthraquinone (H4eAQ) and the transformation of OXO to 2-ethylanthrone and other degradation products are remarkably inhibited. In particular, the formation of 2-ethylanthrone via hydrogenolysis of OXO isomer is strongly suppressed. The Cs-doped catalyst exhibits the highest activity to OXO among all the catalysts tested whereas the ability of Cs-doped catalysts to the formation of anthrone is most effectively inhibited. The role of alkali modifiers is considered to be associated with stronger interactions between the catalyst and quinone reagents, and in particular OXO isomer. Moreover, in the reagent adsorption the centres of support nearby the palladium particles may also participate by affecting the mode of reagents adsorption.

A new synthesis method of hydrogen peroxide was investigated by the photoreduction of 2-ethylanthraquinone (AQ) in water-insoluble organic solvents. Through optimizing the photoreduction condition including solvent, atmosphere and irradiated time, the photolysis system of 1,3,5-trimethylbenzene/trioctyl phosphate (3:1) solvent mixture under oxygen atmosphere was found to give a high yield of hydrogen peroxide. Furthermore, the formation mechanism of hydrogen peroxide was proposed, i.e. photoreduction and subsequent oxidation of AQ. The photoreduction of 2-ethylanthraquinone undergoes the hydrogen abstraction from solvent to form the anthrahydroquinone, which is subsequently oxidized by oxygen to give hydrogen peroxide.

Spherical Al2O3 and SiO2–Al2O3 supports with different silica contents have been synthesized by the oil column method. After impregnation with Na2PdCl4 solution and subsequent calcination, PdO/Al2O3 and PdO/SiO2–Al2O3 catalyst precursors were obtained. X-ray powder diffraction and low temperature N2 adsorption–desorption measurements showed that the addition of silica increased the thermal stability, surface acidity, specific surface area and total pore volume of the spherical alumina. Temperature programmed reduction and H2–O2 titration indicated that Pd supported on the SiO2–Al2O3 spheres possessed higher dispersion and smaller particle size than that supported on pristine spherical Al2O3. Catalytic hydrogenation of ethylanthraquinone using molecular hydrogen was studied over the reduced Pd/Al2O3 and Pd/SiO2–Al2O3 catalysts with different silica contents. Under identical reaction conditions, the reaction activity and stability increased with increasing silica content.

This paper reports a comparative study of the electrochemical performance of in situ hydrogen peroxide electrogeneration on gas diffusion electrodes modified by organic redox catalysts 2-ethylanthraquinone, 2-terc-butylanthraquinone and azobenzene in medium of 0.1 mol L-1 H2SO4 plus 0.1 mol L-1 K2SO4, pH = 1. Hydrogen peroxide generation proved strongly dependent on the applied potential and on the concentration of added catalysts. Electrode modifications led to a significant increase in H2O2 yield (30%) reaching 850 mg L-1, and the overpotential for oxygen reduction shifted to less negative values (400 mV vs Ag/AgCl for electrodes modified by quinones and 300 mV vs Ag/AgCl for electrodes modified by azobenzene) compared to noncatalyzed gas diffusion electrodes, resulting in reduced energy consumption of 596.5 to 232.4 kWh kg-1. The results indicated that the best electrode for H2O2 electrogeneration is the gas diffusion electrode modified with 10% of 2-ethylanthraquinone, offering the best cost to benefit ratio.

This paper reports an investigation on the performance of a catalyzed H2O2 electrogeneration process using a modified oxygen-fed graphite/PTFE electrodes in which the redox catalyst was incorporated into the graphitic mass. The organic redox catalyst chosen for the modification was 2-ethylanthraquinone (EAQ). The H2O2 electrogeneration rate was optimized relative to potential and catalyst concentration. Hydrogen peroxide formation rate on oxygen-fed graphite/PTFE was greatly improved by the presence of the organic redox catalyst and the overpotential for oxygen reduction was shifted more positive. During electrolysis, hydrogen peroxide electrogeneration reaction showed a pseudo-zero-order kinetics and apparent rate constants increased with EAQ concentration. For the electrodes containing 10% of EAQ, apparent rate constants were 30% higher at a potential 400 mV more positive when compared to the performance of a non catalyzed electrode.

Skeletal Ni catalysts (RQ Ni) prepared by alkali leaching of rapidly quenched Ni–Al alloys have been systematically characterized, focusing on the effect of the cooling rate during alloy preparation. It is found that the residual Al content, texture, structure, surface hydrogen species, and active sites of the RQ Ni catalysts can be controlled by the cooling rate of the Ni–Al alloys. In liquid-phase hydrogenation of 2-ethylanthraquinone (eAQ), the RQ Ni catalyst with higher cooling rate favors hydrogenation of the carbonyl group and retards the saturation of the aromatic ring and the formation of the degradation products, thus leading to a higher yield of H 2 O 2 . Based on the characterizations, the improved selectivity is ascribed to the dominant population of strongly chemisorbed hydrogen, which is inactive for the hydrogenation of the aromatic ring, along with the electronic interaction between residual metallic Al and Ni, favoring a carbonyl group-bonded configuration of eAQ on the catalyst.

The effect of water and NaOH was studied on the hydrogenation of 2-ethylanthraquinone (eAQ) over alumina supported 2% Pd/Al2O3-A and 1.2% Pd/Al2O3-B catalysts. The hydrogenation was performed in a fixed-bed reactor by circulating the eAQ solution (the concentration of eAQ was 60 g/dm3) at 50 °C and 5 bar hydrogen pressure. The egg-shell catalysts were prepared by the precipitation of palladium hydroxide onto the support A (activated alumina, preimpregnated with NaH2PO4) or support B (alumina containing 10% SiO2, and preimpregnated with Na2SiO3). Prior to the hydrogenation, the catalysts were dried and pre-treated with water vapour or NaOH solution. The effect of water and NaOH on the amount of active quinones (eAQ and 2-ethyl-5,6,7,8-tetrahydroanthraquinone, H4eAQ) and in particular the role of such reagents in the consumption of aromatic hydroquinone eAQH2, the primary product of the quinone system of eAQ reduction was examined. The saturation of the phenyl rings in eAQH2 produces H4eAQH2, which is a reactive compound and the hydrogenolysis of the C−O bond in the tautomerized eAQH2 leads to other degradation products. Water and NaOH influence the hydrogenation of C O and the hydrogenolysis of C−O bond but have no effect on the hydrogenation of the aromatic rings. The increase in activity in the former C O to C−OH reduction did not depend of alumina A and B as well as the type of reagent (NaH2PO4 or Na2SiO3) introduced to alumina during the catalyst preparation. These reagents however, influenced the course of degradation processes. Water when introduced to the catalyst exhibited unprofitable effect on maintenance the activity of catalyst during the hydrogenation run. Such an unprofitable role is related to influence of water on the course of reactions yielding degradation products.

Liquid-phase hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone has been investigated over Raney Ni, nanosized amorphous Ni–B, and chromium-modified Ni–B catalysts. It has been found that the amorphous Ni–B and chromium-modified Ni–B catalysts exhibited superior selectivity, whereas the chromium-modified Ni–B catalysts had better activity and selectivity than unmodified Ni–B catalyst. Based on the characterizations, the higher selectivity of the amorphous catalysts is ascribed to the dominant population of the strongly bound hydrogen, which is not reactive for the hydrogenation of the aromatic ring, along with the repulsive interaction between the aromatic ring and the electron-rich Ni due to electron donation from alloying B. The addition of chromium decreased the particle size of the amorphous catalysts, which is beneficial for the improvement of activity. Moreover, surface chromium oxide can function as a Lewis acid, which lowers the π CO * orbital of the reactant, favoring a carbonyl group-bonded configuration. The best selectivity was achieved over the Ni–Cr–B2 catalyst, where the hydrogenation of the aromatic ring was thoroughly blocked before the saturation of the carbonyl groups.

The effects of pore structure on the reaction rates and selectivities in the liquid-phase hydrogenation of 2-ethylanthraquinone over Ni B amorphous alloy catalysts prepared by the reductant-impregnation method were studied using regular (HMS, MCM-41, and SBA-15) and commercial mesoporous silicas as supports. The composition, particle size, and location of the Ni B particles were profoundly influenced by the pore structure of the supports. It is found that the location of the Ni B particles depended on the pore size of the supports, whereas the uniformity of particle size was related to the interaction between the Ni B particles and the supports. The hydrogenation rate was much faster on Ni B catalysts with pore diameters exceeding 5 nm than on the narrow-pore catalysts, whereas the selectivity to 2-ethyldihydroanthraquinone, the carbonyl group hydrogenation product, was higher on Ni B catalysts supported on regular mesoporous silicas. The best activity and selectivity were achieved when using SBA-15 as the support, which is attributable to the formation of more uniform active sites due to the unique pore structure of SBA-15.

A series of La-doped Ni–B amorphous alloy catalysts were prepared by a KBH4 reduction method. Ni powders were prepared by hydrazine reduction. These samples were characterized by inductively coupled plasma (ICP), BET, XRD, X-ray photoelectron spectroscopy (XPS), H2-chemisorption, H2-TPD, etc., and studied in the hydrogenation of 2-ethylanthraquinone (EAQ). The Ni–B amorphous alloy catalysts showed higher specific surface area, higher extents of H2-chemisorption and higher H2-TPD areas than Ni powders. In Ni–B amorphous alloys, with the addition of La, the extents of H2-chemisorption and H2-TPD areas first increased markedly and then decreased, with the maximum appeared at the atomic ratio of La to Ni of 0.034. The hydrogenation activity also showed the same trend. The effects of La were attributed to its dispersion of Ni particles, resulting in the formation of more surface Ni centers. However, much higher La contents may result the coverage of surface Ni centers. After heat treatment at higher temperatures, the amorphous structure of Ni–B was destroyed.

An environmentally benign SBA-15-supported amorphous nickel boride alloy catalyst, prepared by a novel reductant–impregnation method, exhibits superior activity, selectivity, and stability in the selective hydrogenation of 2-ethylanthraquinone (eAQ) to 2-ethylanthrahydroquinone (H 2 eAQ), which is the dominating process for the production of hydrogen peroxide in industrial scale. The unique characters of the amorphous alloy as well as the pore structure of the mesoporous SBA-15 molecular sieve are crucial for the excellent catalytic behavior of the title catalyst.

A novel skeletal Ni catalyst, prepared by alkali leaching of a Ni–Al alloy obtained by the rapid quenching technique, exhibited higher selectivity in hydrogenation of 2-ethylanthraquinone to “active quinones” than that of the Raney Ni catalyst originating from a conventional alloy. It is suggested that the structural defects of the rapidly quenched alloy lead to a high population of the strongly bound hydrogen, which is essential for selective hydrogenation of the carbonyl group.

By doping of polyaniline (PANI) in PdCl2 aqueous and ethanol solutions the catalysts containing crystalline and colloidal Pd particles of different sizes were prepared. The size of palladium particles present in Pd/PANI catalysts (characterised by SEM and XRD methods) influenced the course of 2‐ethylanthraquinone (eAQ) hydrogenation, a key step in the industrial production of H2O2. The presence of large palladium particles promotes reactions leading to the formation of the so‐termed “degradation products” not capable of hydrogen peroxide formation.

The liquid phase hydrogenation of 2-ethylanthraquinone (eAQ) was carried out in a slurry reactor in the presence ofPd/SiO2 catalyst at atmospheric pressure of hydrogen in temperature range 18–62°C. 2-ethylanthrahydroquinone (eAQH2) was initially formed with a selectivity close to 100%. In the further process termed ‘deep hydrogenation’ 2-ethyltetrahydroanthraquinone (H4eAQ) was formed as the main product. eAQH2 was also partly converted into other products, which were chromatographically separated and partly identified. A plausible reaction pattern including competitive (hydrogenation and hydrogenolysis) as well as consecutive reactions is postulated. Depending on the catalyst amount, grain size and temperature, deep hydrogenation was controlled by chemical reaction, internal diffusion or external mass transport processes. The influence of such different reaction regimes on the course of reaction and especially the yield of H4eAQ has been discussed on the basis of the proposed reaction pattern. The highest yield of H4eAQ was observed when reaction kinetics was controlled by external mass transport processes.

Hydrogenation of 2-ethylanthraquinone (eAQ) was carried out in a slurry reactor over Pd/SiO 2 catalyst at atmospheric pressure of H 2 and room temperature. During hydrogenation 2-ethylanthrahydroquinone (eAQH 2 ) was initially formed with a selectivity close to 100%. In the further process eAQH 2 was hydrogenated and 2-ethyltetrahydroanthrahydroquinone (H 4 eAQH 2 ) as the main product was formed in high yield (about 55–75%). eAQH 2 was also partly converted into other products termed ‘degradation products’. The rate of hydrogenation, the yield of H 4 eAQH 2 and the type of degradation products were examined as a function of the amount of catalyst. A complicated reaction pattern including consecutive (hydrogenation of aromatic rings) as well as parallel (hydrogenolysis of the carbon-oxygen bonds in eAQH 2 ) processes is postulated.

The effects of the type of support and Pd concentration profile in alumina and silica supported egg-shell catalysts and their performance in the hydrogenation of 2-ethylanthraquinone (eAQ) were studied in 'Anthra' (AQ) and 'All-Tetra' systems. The activity and deactivation of catalysts were determined in the fixed-bed reactor. Solution saturated with hydrogen, (concentration of active quinones 60g/dm3, eAQ in the AQ system, 30% of eAQ and 70% of H4eAQ–2-ethlytetrahydroanthraquinone, in the All-Tetra system) was circulated through the catalyst bed at temperature 50°C and pressure 5bar. The contents of eAQ, active quinones, H4eAQ and degradation products were determined in the course of hydrogenation by GC method. The egg-shell palladium catalysts (1–2wt% Pd) prepared by the precipitation of palladium hydroxide onto alumina and silica supports pre-impregnated with various alkaline (NaHCO3, NaH2PO4, Na2SiO3) solutions were used in the hydrogenation experiments. Pd concentration profile inside the grains of catalysts was characterized by scanning electron microscopy. A difference between alumina and silica carriers with respect to the course of side reactions producing degradation products was found. Degradation of quinones in the hydrogenolytic reactions predominated on alumina supported catalysts, while the catalysts with silica favoured the hydrogenation of aromatic rings resulting in H4eAQ-active quinone. As a crucial factor for the decrease in the activity during the hydrogenation run, the reactivity of catalyst in the hydrogenolytic reactions was established. Alumina supported catalysts exhibited much higher deactivation than those of silica supported ones. Silica carrier as well as silica species introduced onto alumina under pre-impregnation with Na2SiO3 exhibited an advantageous role in the catalyst performance, in terms of activity and deactivation.

The chemical incorporation of palladium into polyaniline (PANI) deposited onto the silica gel microparticles (15-μm in diameter) was studied. The as-prepared silica particles coated with PANI–hydrochloride (AC) were treated with aqueous ammonia solution (0.1 M) to transform polyaniline to its base (BA) form. Both AC and BA samples were reacted with PdCl 2 solutions (2.3×10 −3 M) strongly differing in the concentration of HCl (0.1 M HCl, series K; 6.6×10 −4 M HCl, series Z). Two series of samples with 0.43–2.14 wt.% Pd were obtained. Fourier-transform infra red (FTIR), UV-Vis, X-ray photoelectron spectroscopies (XPS) and scanning electron microscopy have been used to examine the nature of processes involved upon insertion of Pd and to characterize palladium species in the final samples. Very similar palladium species were found in the polymer matrix independently of the acidity of PdCl 2 solutions and the extent of PANI protonation (AC and BA samples). Pd 2+ was the only form if no more than 0.86% Pd was introduced. Incorporation of higher content of palladium resulted in the partial reduction (14.6–28.7%) of Pd 2+ to Pd 0 . The presence of Pd 2+ species in the form of complexes in which besides Cl − ligands also nitrogen groups of PANI participated has been postulated. The catalytic properties of Pd/PANI-SiO 2 have been studied in the liquid-phase hydrogenation of 2-ethylanthraquinone (EAQ) at 60 °C under 1 atm of hydrogen. Very low activity of the as-prepared catalysts significantly increased due to reduction of the samples with NaH 2 PO 2 and subsequently with dihydrogen. The specific activities of reduced series K and Z samples were comparable and the maximum activity exhibited catalysts with 1–1.5% Pd.

A nanosized amorphous Ni-Cr-B catalyst prepared by the chemical reduction method exhibited superior thermal stability and selectivity in hydrogen peroxide synthesis via the anthraquinone route.

1. A study was made of the hydrogenation of 2-ethylanthraquinone at 20° in dioxane, an alcohol-dioxane mixture, and N,N-dimethylformamide in presence of Raney nickel. 2. In N,N-dimethylformamide addition of only one molecular proportion of hydrogen occurs. In dioxane and an alcohol-dioxane mixture the aromatic side nuclei of 2-ethylanthraquinone are also hydrogenated at an appreciable rate. 3. With increase in the amount of catalyst its specific activity in the hydrogenation reaction increases. This behavior is probably associated with the chemical nonuniformity of hydrogen in a highly active catalyst.

1. The selectivity of the hydrogenation of 2-ethylanthraqulnone on skeletal nickel catalyst in dioxane solution is practically independent of both the amount of catalyst and the temperature in the interval 20–80°. 2. Steam-treated nickel catalyst selectively catalyzes the hydrogenation of 2-ethylanthraquinone to the hydroquinone.