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Copper chromite
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.031.806 |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| Cu2Cr2O5 | |
| Molar mass | 311.0812 g/mol |
| Appearance | grey powder |
| Density | 5.42 g/cm3[1] |
| Hazards | |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 1 mg/m3 (as Cu)[2] |
REL (Recommended)
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TWA 1 mg/m3 (as Cu)[2] |
IDLH (Immediate danger)
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TWA 100 mg/m3 (as Cu)[2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Copper chromite often refers to inorganic compounds with the formula Cu2Cr2Ox. They are black solids. Cu2Cr2O4 is a well-defined material. The other copper chromite often is described as Cu2Cr2O5. It is used to catalyze reactions in organic chemistry.[3]
History
[edit]Copper chromite was first described in 1908.[4] The catalyst was further developed by Homer Burton Adkins and Wilbur Arthur Lazier, partly based on interrogation of German chemists after World War II in relation to the Fischer–Tropsch process.[5][6] For this reason it is sometimes referred to as the Adkins catalyst or the Lazier catalyst. Adkins was the first to incorporate barium into the structure, which prevents the catalyst from being reduced to an inactive form during hydrogenation reactions.[7]
Chemical structures
[edit]The stoichiometry of the Laziar or Adkins catalyst is not well defined, thus the structure of their material is not defined either.[8]
The oxidation states for the constituent metals in Cu2Cr2O4 are Cu(II) and Cr(III).[9] A variety of compositions are recognized for the substance, including Cu2CrO4·CuO·BaCrO4 (CAS# 99328-50-4), Cu2Cr2O5 (CAS# 12053-18-8), and Cr2CuO4.[10] Commercial samples often contain barium oxide and other components.
Production
[edit]Copper chromites catalyst are produced by thermal decomposition of diverse precursors. The traditional method is by the calcining of copper chromate:[11]
- 2 CuCrO4 → 2 CuCrO3 + O2
Copper barium ammonium chromate is the most commonly used substance for production of copper chromite. The resulting copper chromite mixture produced by this method can only be used in procedures that contain materials inert to barium, as barium is a product of the decomposition of copper barium ammonium chromate, and is thus present in the resulting mixture. The by-product copper oxide is removed using an acetic acid extraction, consisting of washing with the acid, decantation and then heat drying of the remaining solid to yield isolated copper chromite. Copper chromite is produced by the exposure of copper barium ammonium chromate to temperatures of 350-450 °C, generally by a muffle furnace:[5]
- Ba
2Cu
2(NH
4)
2(CrO
4)
5 → CrCuO
3 + CuO + 2 Ba + 4 H
2O + 4 Cr + N
2 + 6 O
2
Copper ammonium chromate is also used for production of copper chromite. It is generally utilized as an alternative to the route of barium ammonium chromate for usage in chemicals reactive with barium. This can also be washed with acetic acid and dried to remove impurities. Copper chromite is produced through the exposure of copper ammonium chromate to temperatures of 350-450 °C:
- Cu(NH
4)
2(CrO
4)
2 → CrCuO
3 + CrO + 4 H
2O + N
2
An active copper chromite catalyst which includes barium in its structure can be prepared from a solution containing barium nitrate, copper(II) nitrate, and ammonium chromate. When these compounds are mixed a resulting precipitate is formed. This solid product is then calcined at 350–400 °C to yield the catalyst:[11]
- Cu(NO3)2 + Ba(NO3)2 + (NH4)2CrO4 → CuCr2O4·BaCr2O4
Illustrative reactions
[edit]
- Hydrogenolysis of ester compounds to the corresponding alcohols. This approach is useful for conversion of fatty acid esters, such as fatty acid methyl esters (FAMEs) to fatty alcohols:
- RCO2CH3 + 2 H2 → RCH2OH + HOCH3
In some cases, alkene groups are hydrogenated.
- Diethyl maleate can similarly be hydrogenated to either butyrolactone or 1,4-butanediol, depending on conditions.[10]
- Sebacoin, derived from the acyloin condensation of dimethyl sebacate, is hydrogenated to 1,2-cyclodecanediol in the presence of this catalyst.[12]
- Phenanthrene is reduced at the 9,10 position.
- Hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol at 250–300 °C under 3300-6000 psi of H2.[13]
- Decarboxylation of α-phenylcinnamic acid to cis-stilbene.[14]
Reactions involving hydrogen are conducted at relatively high gas pressure (135 atm) and high temperatures (150–300 °C) in a so-called hydrogenation bomb. More active catalysts, such as W-6 grade Raney nickel, also catalyze hydrogenations such as ester reductions. The latter catalyst benefits from requiring less vigorous conditions (i.e., it works at room temperature under similar hydrogenation pressures) but requires a higher ratio of catalyst to reagents.[12]
See also
[edit]References
[edit]- ^ Dollase, W. A.; O'Neill, H. St. C. (1997). "The Spinels CuCr2O4and CuRh2O4". Acta Crystallographica Section C Crystal Structure Communications. 53 (6): 657–659. Bibcode:1997AcCrC..53..657D. doi:10.1107/S0108270197000486.
- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0150". National Institute for Occupational Safety and Health (NIOSH).
- ^ Cladingboel, D. E. "Copper Chromite" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons. doi:10.1002/047084289X.rc221
- ^ Gröger, Max (1912). "Chromite aus basischen Chromaten". Zeitschrift für Anorganische Chemie. 76: 30–38. doi:10.1002/zaac.19120760103.
- ^ a b Adkins, Homer; Burgoyne, Edward; Schneider, Henry (1950). "The Copper—Chromium Oxide Catalyst for Hydrogenation". Journal of the American Chemical Society. 72 (6): 2626–2629. Bibcode:1950JAChS..72.2626A. doi:10.1021/ja01162a079.
- ^ Fischer–Tropsch Archive
- ^ Connor, Ralph.; Folkers, Karl.; Adkins, Homer. (May 1931). "The Preparation of Copper-Chromium Oxide Catalysts for Hydrogenation". Journal of the American Chemical Society. 53 (5): 2012. Bibcode:1931JAChS..53.2012C. doi:10.1021/ja01356a511.
- ^ Capece, F.M.; Castro, V.Di; Furlani, C.; Mattogno, G.; Fragale, C.; Gargano, M.; Rossi, M. (1982). ""Copper chromite" Catalysts: XPS structure elucidation and correlation with catalytic activity". Journal of Electron Spectroscopy and Related Phenomena. 27 (2): 119–128. Bibcode:1982JESRP..27..119C. doi:10.1016/0368-2048(82)85058-5.
- ^ Prince, E. (1957). "Crystal and Magnetic Structure of Copper Chromite". Acta Crystallographica. 10 (9): 554–556. Bibcode:1957AcCry..10..554P. doi:10.1107/S0365110X5700198X.
- ^ a b Rylander, Paul N. (2000). "Hydrogenation and Dehydrogenation". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a13_487. ISBN 3-527-30673-0.
- ^ a b Lazier, W. A.; Arnold, H. R. (1939). "Copper Chromite Catalyst". Organic Syntheses. 19: 31. doi:10.15227/orgsyn.019.0031.
- ^ a b Blomquist, A. T.; Goldstein, Albert (1956). "1,2-Cyclodecanediol". Organic Syntheses. 36: 12. doi:10.15227/orgsyn.036.0012.
- ^ Kaufman, Daniel; Reeve, Wilkins (1946). "1,5-Pentanediol". Organic Syntheses. 26 (83): 83. doi:10.15227/orgsyn.026.0083.
- ^ Buckles, Robert; Wheeler, Norris (1953). "cis -Stilbene". Organic Syntheses. 33: 88. doi:10.15227/orgsyn.033.0088.
External links
[edit]- CAS registry [7440-47-3] & [1317-38-0]
Copper chromite
View on Grokipediafrom Grokipedia
Properties
Chemical composition
Copper chromite is classified as a transition metal chromite inorganic compound, comprising copper, chromium, and oxygen in a mixed oxide structure. The primary formula for copper chromite is , with a molar mass of 311.08 g/mol. An alternative formula is , which represents the stoichiometric spinel phase with a molar mass of 231.5 g/mol.[3] Due to variations in preparation and composition, copper chromite catalysts are often non-stoichiometric mixtures including the spinel phase and excess CuO, commonly approximated as or . In the spinel lattice of copper chromite, copper adopts the +2 oxidation state (Cu(II)) and chromium the +3 oxidation state (Cr(III)).[4] Commercial variants used as catalysts incorporate promoters like barium oxide (BaO) for improved performance; a typical formulation includes 62-64% , 22-24% CuO, and 6% BaO, with trace amounts of graphite (0-4%), (1%), and (1%).Physical characteristics
Copper chromite is typically observed as a black to grey powder, depending on the preparation method and particle size. This fine particulate form contributes to its utility in catalytic and pigment applications, where a uniform dispersion is essential.[5][6] The material has a density of 5.4 g/cm³, reflecting its compact oxide structure. It is insoluble in water, with no measurable dissolution under standard conditions, and similarly resistant to dilute acids. Copper chromite demonstrates good stability in air at room temperature and maintains integrity up to high temperatures, decomposing only above 900°C. Its molar mass is 311.08 g/mol, corresponding to the composition Cu₂Cr₂O₅.[7][5][7] Under normal conditions, copper chromite is non-flammable, posing no ignition risk in dry storage or handling. However, it acts as an oxidizer, capable of intensifying combustion when in contact with flammable materials. Additionally, due to its stable black coloration, it serves as an inorganic pigment in ceramics and paints, providing durable tinting with resistance to fading.[6][8]Crystal structure
Copper chromite, represented by the formula CuCr₂O₄, exhibits a normal spinel structure in which Cu²⁺ cations occupy tetrahedral sites and Cr³⁺ cations occupy octahedral sites. This arrangement forms the basis of its lattice, typically manifesting as a tetragonally distorted spinel (hausmannite type) with space group I₄₁/amd, though cubic variants can occur under certain conditions.[9][10] X-ray diffraction (XRD) analysis consistently confirms the presence of the CuCr₂O₄ spinel phase, with characteristic peaks indicating high crystallinity and phase purity in annealed samples, often exceeding 98% for the tetragonal form. Non-stoichiometric compositions, such as slight deviations from the ideal Cu:Cr:O ratio of 1:2:4 (e.g., Cu/Cr ≈ 1/1.93), introduce lattice defects that influence structural stability without altering the overall spinel framework.[11][12] In thin film forms, copper chromite maintains the tetragonal spinel structure, displaying nanocrystalline grains of 10–25 nm with minor defect phases like CuO at grain boundaries. These films exhibit an energy gap below 0.5 eV and broad optical absorption across the solar spectrum from 300 to 2500 nm. Scanning electron microscopy (SEM) reveals particle morphologies in nano-sized copper chromite as predominantly spherical or quasi-spherical, with sizes typically in the 20–100 nm range, highlighting the material's tendency toward homogeneous aggregation in powdered forms.[12][13][14]History
Discovery
Copper chromite, an inorganic compound with the approximate formula Cu₂Cr₂O₅, was first described in 1908 by German inorganic chemist Otto Gröger, who synthesized it through the thermal decomposition of copper chromates and designated it as copper chromite.[15] Gröger's preparation involved heating mixtures of copper and chromium compounds at elevated temperatures, yielding a black solid material that demonstrated notable resilience under such conditions.[15] This initial synthesis highlighted the compound's thermal stability, as it withstood the high-temperature ignition processes without significant decomposition, a property observed in early experiments on mixed metal oxides.[15] The discovery occurred within the broader context of early 20th-century inorganic chemistry, where researchers explored synthetic analogs to natural chromite minerals like FeCr₂O₄, focusing on spinel-structured oxides of transition metals.[1] Copper chromite, sharing a similar spinel crystal lattice, was investigated for its structural parallels to these minerals, contributing to understanding oxide formation and stability in refractory materials.[16] Additionally, its deep black coloration prompted early considerations of its potential as an oxide pigment, though primary focus remained on fundamental synthesis and characterization rather than applied uses.[1] Early nomenclature for the compound varied, reflecting its composition of CuO and Cr₂O₃ components. Gröger's work, detailed in Zeitschrift für anorganische Chemie, provided the foundational chemical identity, setting the stage for subsequent studies on its properties.[15] This pre-catalytic recognition of its robustness at high temperatures foreshadowed later advancements in its application as a hydrogenation catalyst in the 1930s.[15]Development as a catalyst
Copper chromite's development as a catalyst began in 1931 when Homer Adkins and his collaborators demonstrated its effectiveness for the hydrogenation of esters to alcohols under moderate conditions of 150–220°C and 100–150 atm pressure, achieving high yields and selectivity for a range of organic compounds.[17] This breakthrough marked a significant advancement over previous catalysts, enabling selective reductions without excessive hydrogenolysis to hydrocarbons.[18] Post-World War II, the catalyst underwent further refinement by researchers including Wilbur A. Lazier at DuPont, building on Adkins' earlier academic work at the University of Wisconsin. These efforts elevated copper chromite to a versatile industrial tool, often referred to as the Adkins catalyst or Lazier catalyst due to their pivotal roles. In the 1950s, key improvements included barium promotion, which enhanced copper dispersion, prevented sintering and over-reduction during high-pressure operations, and improved stability for demanding reactions like ester hydrogenations.[19] This modification facilitated broader industrial adoption, scaling up production for applications in alcohol synthesis from fatty esters and other bulk chemical processes.[20] From 2020 to 2025, copper chromite has received renewed attention in green chemistry for enabling low-carbon hydrogenation pathways, such as in the chemical recycling of bio-based polyesters like PLA to value-added products.[21] Concurrently, nano-variants of the catalyst have emerged, offering higher surface areas and improved activity for selective reductions in sustainable propellant production.[22]Production
Laboratory methods
Copper chromite (Cu₂Cr₂O₅) can be prepared in laboratory settings through several small-scale methods, primarily aimed at producing high-purity catalyst powders for research applications. These techniques emphasize controlled precipitation, decomposition, or sintering of metal precursors to form the spinel structure, often followed by purification steps to remove impurities like excess oxides. The active phase is typically the CuCr₂O₄ spinel embedded within the Cu₂Cr₂O₅ matrix.[23] One common approach is coprecipitation, where solutions of copper and chromium salts are mixed in the presence of a precipitating agent. For example, copper sulfate (CuSO₄) and ammonium dichromate ((NH₄)₂Cr₂O₇) are dissolved in water, and ammonium hydroxide is added to precipitate basic copper ammonium chromate, which is then filtered, dried at 100–110°C, and calcined at 350–450°C to yield the spinel phase.[23] An alternative variant, known as the Adkins method, uses cupric nitrate trihydrate and ammonium dichromate with ammonium hydroxide, followed by drying and ignition, producing approximately 113 g of catalyst from the specified precursors. Thermal decomposition involves heating complex chromate precursors in a controlled atmosphere. Ammonium copper chromate ((CuNH₄)₂(CrO₄)₂) is dried and then decomposed in a muffle furnace at around 350–500°C, releasing ammonia and forming the active copper chromite.[23] Similarly, copper barium ammonium chromate, prepared by mixing barium nitrate and copper nitrate solutions with ammonium chromate, is dried at 110°C and heated at 350–450°C for 1 hour, followed by extraction with dilute acetic acid to remove barium residues, yielding 130–140 g of fine black powder.[15] The ceramic method entails solid-state sintering of metal oxides. Copper(II) oxide (CuO) and chromium(III) oxide (Cr₂O₃) are intimately mixed in appropriate ratios (e.g., Cu:Cr = 1:1), pelletized, and calcined at high temperatures of 800–1000°C for several hours to promote diffusion and phase formation, though this results in lower surface area materials compared to wet methods.[23] Recent advancements in the 2020s have focused on nano-synthesis for ultrafine particles, particularly for specialized uses like propellant catalysts. A notable technique is the thermal decomposition of ammoniac copper oxalate chromate (CuC₂O₄·NH₄CrO₄·NH₃), synthesized from copper oxalate and ammonium chromate, followed by calcination at 350°C in air or inert atmosphere to produce nanostructured Cu₂Cr₂O₅ with particle sizes below 100 nm. Hydrothermal methods, such as reacting copper and chromium precursors (e.g., nitrates) in a basic medium at 180°C for 12 hours, also yield monodispersed Cu₂Cr₂O₅ nanoparticles around 20–50 nm, confirmed by high-resolution imaging. Laboratory preparations typically achieve yields of 80–90% based on metal content, with purity assessed through X-ray diffraction (XRD) to verify the tetragonal spinel phase and detect impurities like CuO or Cr₂O₃.[23] Post-synthesis washing and selective dissolution enhance phase purity to over 95% in optimized runs.[15]Industrial processes
The primary industrial method for manufacturing copper chromite catalysts is the thermal decomposition of precursors, such as basic copper ammonium chromate or copper oxalate chromate, in large-scale furnaces at temperatures between 350 and 450°C. This process facilitates the formation of the spinel-structured Cu₂Cr₂O₅ phase, which is critical for the catalyst's efficacy in high-pressure reactions. Industrial furnaces are designed for controlled atmospheres to optimize yield and minimize impurities, with decomposition typically completed in hours to ensure phase purity.[24] Promoters are integrated during precursor preparation to enhance thermal stability and prevent sintering under operational conditions. Barium, for example, is added to improve copper dispersion and maintain activity, while graphite serves as a structural template in select formulations; typical compositions include about 1% CrO₃ or Cr₂O₃ to bolster overall stability without altering the core spinel matrix. These additions are incorporated via co-precipitation or mixing prior to decomposition, allowing for tailored catalyst performance in demanding environments.[24][2] Continuous production routes have been optimized for commercial scalability, involving coprecipitation of aqueous copper and chromium salts with ammonia or sodium hydroxide, followed by spray drying to produce uniform particles (typically 10-50 μm) and final calcination at 400-500°C. This sequence ensures consistent particle size distribution and high throughput, suitable for meeting bulk demands in catalyst manufacturing plants. Spray drying, in particular, prevents agglomeration and supports downstream pelletization for reactor use.[2][24] As of 2025, the global market for copper chromite production is valued at approximately 250 million USD, largely propelled by its role in petrochemical hydrogenation processes for refining and chemical synthesis; recent innovations in advanced thermal decomposition have enabled nano-variants with increased surface areas up to 100 m²/g for improved efficiency. Quality control measures, including in-line X-ray diffraction (XRD) monitoring, verify the exclusive spinel phase formation, while process parameters are adjusted to avoid over-reduction, which could generate inactive metallic copper and compromise longevity.[25][26][24]Applications
Hydrogenation catalysis
Copper chromite serves as a highly effective heterogeneous catalyst for the hydrogenation of esters to alcohols, particularly in the production of fatty alcohols from methyl esters. This reaction is industrially significant for converting vegetable oil-derived esters into valuable intermediates for surfactants and detergents. The process typically operates at elevated temperatures of 150-300°C and hydrogen pressures around 135 atm (approximately 2000 psi), enabling selective cleavage of the ester C-O bond without excessive reduction to hydrocarbons.[27][28] The catalytic mechanism involves bifunctional sites on the reduced copper chromite surface, where Cu⁰ sites facilitate the dissociative activation of H₂ to generate atomic hydrogen, while Cr-containing spinel phases provide acidic sites for substrate adsorption and proton supply. Esters bind via their carbonyl group to these acidic Cr sites, promoting hydrogenolysis to form the corresponding alcohols, with electrons transferred from metallic Cu to support the reduction. This synergy contrasts with Raney nickel catalysts, which exhibit lower selectivity for ester hydrogenolysis due to stronger adsorption and over-reduction tendencies, often leading to hydrocarbon byproducts; copper chromite's milder activity ensures higher yields of alcohols under similar conditions.[29][30] Industrial applications frequently employ vapor-phase fixed-bed reactors, where barium-promoted variants of copper chromite enhance thermal stability and resist sintering during prolonged operation. A representative example is the selective hydrogenation of methyl esters from soybean or rapeseed oils, yielding fatty alcohols via the general equation:
This process achieves high conversion rates, with iodine value reductions indicating effective saturation of unsaturated bonds while preserving alcohol selectivity above 90% in optimized setups.[27]
In petrochemical processes, copper chromite demonstrates robust activity, often outperforming alternatives in large-scale ester hydrogenations due to its cost-effectiveness and recyclability.