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High-pressure synchrotron X-ray diffraction and infrared absorption spectroscopy have been employed to study the crystal chemistry and phase transitions in an [OH]-bearing carbonate, malachite Cu2(CO3)(OH)2, to determine the effect of [OH] on the stability of carbonate. We found that the crystal structure of malachite is stabilized by a high degree of [CuO6]-octahedron distortion, as is manifested by large variations in Cu–O bond lengths resulting from oxygen atoms that connect to hydrogen at crystallographically different sites. External pressure offsets the effect of hydrogen bond, promotes [CuO6] compression and regularization and accordingly [CO3] rotation. Rotation of [CO3]-triangles, in turn, assists in a conversion in the crystal orientation of the [CuO6] structural unit. During compression to above ~6 ​GPa, malachite begins to turn into the rosasite lattice, accompanied with a jump in density of 3.3%. Rosasite is characterized with a hardened lattice and preserves to the maximum pressure (18.2 ​GPa) of the present study. Phase transformation mechanism of malachite to rosasite is different from that of carbonates, with the latter being driven by an almost uniform compression of [MO6]-octahedron (M ​= ​Ca, Cd, Mn, Fe, Zn, Mg, etc.) and rotation/translation of [CO3]-triangle under pressure.

Aluminum is an important ingredient in the ternary Cu/ZnO/Al2O3 catalyst for methanol synthesis from syngas. The objective of this work is to investigate the effect of Al addition methods on the property of Cu/ZnO/Al2O3 catalyst. A series of Cu0.6Zn0.3Al0.1 catalysts with various Al-containing precursors were prepared by co-precipitation and fractional-precipitation methods. The catalyst samples were characterized by XRD, TG-MS, XRF, N2 physisorption and TPR. Results show that the Al addition methods have strong effect on the substitution of Cu by Zn in the subcarbonate lattice, leading to various performances of the obtained catalysts. Al addition with fractional precipitation performed higher substitution of Cu than that with the traditional co-precipitation method. And thus, it can be a promising method for preparing the Cu/ZnO/Al2O3 methanol synthesis catalyst.

The crystal structure of cobalt carbonate hydroxide Co2CO3(OH)2, a solid important in materials and environmental science, is investigated using density functional theory (DFT) simulations and powder X-ray diffraction (PXRD) measurements., The cobalt carbonate hydroxide Co2CO3(OH)2 is a technologically important solid which is used as a precursor for the synthesis of cobalt oxides in a wide range of applications. It also has relevance as a potential immobilizer of the toxic element cobalt in the natural environment, but its detailed crystal structure is so far unknown. The structure of Co2CO3(OH)2 has now been investigated using density functional theory (DFT) simulations and powder X-ray diffraction (PXRD) measurements on samples synthesized via deposition from aqueous solution. Two possible monoclinic phases are considered, with closely related but symmetrically different crystal structures, based on those of the minerals malachite [Cu2CO3(OH)2] and rosasite [Cu1.5Zn0.5CO3(OH)2], as well as an orthorhombic phase that can be seen as a common parent structure for the two monoclinic phases, and a triclinic phase with the structure of the mineral kolwezite [Cu1.34Co0.66CO3(OH)2]. The DFT simulations predict that the rosasite-like and malachite-like phases are two different local minima of the potential energy landscape for Co2CO3(OH)2 and are practically degenerate in energy, while the orthorhombic and triclinic structures are unstable and experience barrierless transformations to the malachite phase upon relaxation. The best fit to the PXRD data is obtained using a rosasite model [monoclinic with space group P1121/n and cell parameters a = 3.1408 (4) Å, b = 12.2914 (17) Å, c = 9.3311 (16) Å and γ = 82.299 (16)°]. However, some features of the PXRD pattern are still not well accounted for by this refinement and the residual parameters are relatively poor. The relationship between the rosasite and malachite phases of Co2CO3(OH)2 is discussed and it is shown that they can be seen as polytypes. Based on the similar calculated stabilities of these two polytypes, it is speculated that some level of stacking disorder could account for the poor fit of the PXRD data. The possibility that Co2CO3(OH)2 could crystallize, under different growth conditions, as either rosasite or malachite, or even as a stacking-disordered phase intermediate between the two, requires further investigation.

Divalent metal hydroxycarbonates with M2CO3(OH)2 stoichiometry are widely used in industry and are abundant in nature as the malachite/rosasite group of minerals. Essential to their performance as catalytic precursors and in nanoelectronics, these materials and minerals exhibit a high degree of cation ordering in mixed metal systems due to differences in distortion of the octahedral metal sites. Density-functional theory (DFT) calculations on pokrovskite Mg2CO3(OH)2 in the rosasite structure and Mg analogues of monoclinic and orthorhombic forms of malachite determine that the octahedral sites are innately distorted, and that d9 Cu(II) Jahn-Teller distortion accommodates this distortion rather than causes it, leading to the significant preference of Cu for the type I octahedral sites. This distortion also leads to a high propensity for formation of cation vacancies charge balanced by proton substitution. Ab initio thermodynamics is used to determine that there are conditions under which proton substitution defects are slightly more stable than the stoichiometric structure, consistent with the widespread observation of such defects in pokrovskite in nature. Pokrovskite itself is most likely to form under CO2-rich/low water conditions, particularly those utilizing supercritical CO2 for carbon sequestration and is sufficiently thermodynamically stable to trap CO2 under geological conditions. Low temperature and high water concentration promotes the formation of proton substitution defects, which has implications for synthesis of any material where octahedral strain may be relieved by proton substitution defects.

Paradsasvarite (IMA No. 2012-077) was found in the Nagy-Lapafő area, Paradsasvar, Matra Mountains, Hungary. It forms pale beige, globular aggregates up to 0.2 mm in diameter on calcite. Associated secondary minerals are smithsonite, hemimorphite, hydrozincite, aurichalcite and rosasite. The mineral was formed as an alteration product of sphalerite and chalcopyrite in a carbonate-rich environment. Paradsasvarite is translucent with a weakly vitreous, dull or silky lustre and white streak. Its Mohs hardness is about 2–3, cleavage and parting were not observed. It is brittle; the fracture is finely fibrous. Average of nine electron-microprobe analyses gave ZnO 58.08, CuO 12.60, PbO 1.27, CO2 (calc.) 19.50, H2O (calc.) 7.94, total 99.39 wt.%, corresponding to the empirical formula (Zn0.62Cu0.36Pb0.01)Σ0.99Zn1.00(CO3)(OH)2. The seven strongest lines in the X-ray powder diffraction pattern are [dhkl in A (Iobs %, hkl)] 6.054 (67, 200), 5.085 (100, 210), 3.703 (87, 310 and 220), 3.021 (25, 400 and 130), 2.971 (25, −211 and 001), 2.603 (62, −221) and 2.539 (36, 420). According to its X-ray powder diffraction data and chemical formula, paradsasvarite belongs to the malachite-rosasite group and it is isostructural with rosasite. It is monoclinic, space group P21/a, a = 12.92(1), b = 9.372(7), c = 3.159(4) A, β = 110.4(1)°, V = 358.5(5) A3, Z = 4.

The crystal structure of kolwezite, (Cu, Co)2(CO3)(OH)2, was refined by Rietveld method from synchrotron X-ray powder data to Rp =4.56%, wRp =6.51%. Kolwezite, P21/a, a= 12.201(1), b=9.354(1), c=3.1494(3)A , b = 98.922(7)°, is isostructural with rosasite. Because of the Jahn-Teller effect, the Me1 polyhedron hosting Cu2þ only is strongly distorted towards a (4þ2) coordination, while the Me2 octahedron, with major Co, is neatly a more regular one. The Me2þ polyhedra are connected through edge-sharing, forming "ribbons" running along [0 0 1] direction. These ribbons are interconnected by corner sharing to form "corrugated" layers, interlinked by the carbonate groups, giving rise to an infinite framework structure, with notationMM=MT. The Rietveld study of synchrotron X-ray powder data of synthetic cobaltoan malachites shows a decrease in unit-cell volume, with an anisotropic contraction of unit-cell parameters, with increasing Co content. The major progressive shortening of apical bonds in Me2 octahedra, with consequent regularization of the Jahn-Teller distorted Cu octahedra, drives a progressive compaction of the malachite structure; it is the main factor accounting for volume contraction in cobaltoan malachites.

Selective conversion of 5-hydroxymethylfurfural (HMF) can produce sustainable fuels and chemicals. Herein, Cu–ZnO catalysts derived from minerals (malachite, rosasite and aurichalcite) were employed for selective hydrogenation of HMF for the first time. High yields of 2,5-dihydroxymethylfuran (~99.1%) and 2,5-dimethylfuran (~91.8%) were obtained tunably over the catalyst with a Cu/Zn molar ratio of 2, due to the well-dispersed metal sites tailored by mineral precursors, well-controlled surface sites and optimized reaction conditions. The relationship between catalytic performance and catalyst properties was elucidated by characterization based on the composition and the structural and surface properties, and catalytic tests. The catalyst can also be extended to selective hydrogenation of other bio-derived molecules (furfural and 5-methylfurfural) to target products. The construction of mineral-derived Cu–ZnO catalysts and the revelation of the structure–performance relationship can be applied to further rational design and functionalization of non-noble Cu catalysts for selective conversion of bio-derived compounds.

We report the results of mineralogical and structural studies of para´dsasva´rite from Rudaba´nya, Hungary, and rosasite from Hayden, Arizona (USA). A preliminary investigation of the two minerals, which belong to the rosasite-malachite group, was conducted using Raman spectroscopy, X-ray diffraction, and EPMA. Para´dsasva´rite has the chemical formula (Zn1.91Cu0.06Mg0.02)R1.99(CO3)(OH)2, ideally Zn2(CO3)(OH)2, and rosasite has the formula (Cu1.14Zn0.84Mg0.02)R2(CO)3(OH)2, matching the general formula CuZn(CO3)(OH)2. The first single-crystal full structural study of rosasite from Hayden, based on synchrotron X-ray data, is reported here and fully confirms the results obtained by Perchiazzi (2006) on the basis of X-ray powder data. The presence of structural disorder in Cu-Zn distribution in these minerals is indicated by the streaking of reflections along c*. Rosasite is monoclinic, P21/a, a 12.2436(29) A? , b 9.3555(19) A? , c 3.1535(6) A? , b¼98.69(3)8, and its crystal structure was refined to R1¼12.4%, wR2¼35.5%. The presence of Cu2þ causes a Jahn-Teller distortion of coordination polyhedra, a major feature of the rosasite crystal structure, particularly evident in the Me1 coordination polyhedron, which is fully occupied by Cu. A Rietveld study of para´dsasva´rite, based on synchrotron radiation data, shows it is isostructural with rosasite, monoclinic P21/a, a 12.253(4) A? , b 9.348(3) A? , c 3.167(1) A? , b ¼ 97.700(4)8, and its crystal structure was refined to R1 ¼ 1.45%, wR2 ¼ 2.45%. The Me1 and Me2 coordination polyhedra in para´dsasva´rite, the former hosting Zn with a minor presence of Cu, the latter fully occupied by Zn, are as expected both more regular than the corresponding polyhedra in rosasite. Crystal-chemical considerations, based on literature chemical data for rosasite and Zn-rich malachite, indicate that a minimum Cu content of 0.4-0.5 apfu is necessary to stabilize the malachite-type structure.

Ternary Cu/ZnO/Al2O3 catalyst systems were systematically prepared by innovative synthesis routes in microstructured synthesis setups, allowing to study different types of micromixers. The coprecipitation in the slit plate and valve-assisted mixers was operated continuously under exact control of pH, temperature, concentration and ageing time. Due to the enhanced surface to volume ratio in microstructured reactors, a precise temperature control and efficient mixing of the reactants are enabled. The precipitation was performed with sodium, ammonium and potassium carbonate as well as sodium hydroxide. To evaluate the potential of the novel synthesis routes, reference samples in a conventional batch process were prepared. The catalysts were synthesized according to the constant pH method with a molar ratio of 60:30:10 for copper, zinc and aluminum. The synthesis routes applied have a significant influence on the structures of hydroxycarbonate precursors and on the catalytic activity in methanol synthesis. XRD patterns of hydroxycarbonate precursors from the synthesis in micromixers, especially using ammonium carbonate as precipitating agent, display high crystallinity and sharp reflections of malachite and rosasite. Cu/ZnO/Al2O3 catalysts prepared in continuously operated micromixers in general show higher specific copper surface areas than catalysts prepared in conventional batch processes. The highest methanol productivity of all prepared catalyst systems was observed with the catalyst precipitated in the slit plate mixer with ammonium carbonate. (C) 2012 Published by Elsevier B.V.

Hydroxycarbonates with the general formula Me2(CO3)(OH)2 are widely used materials in industrial processes and are widespread in nature. The Cu term, malachite, Cu2CO3(OH)2, is monoclinic, P21/a. Substitution of Cu2+ with other bivalent cations such as Mg, Zn, Fe, Cu or Ni is possible and leads to a different structure type, rosasite, P21/a or P21/b11 in the same cell setting as malachite. Rosasite structure is topologically similar to malachite, but the symmetry elements are oriented differently with respect to structural units. The stability of the malachite-like structure (MS) compared with the rosasite-like structure (RS) has been suggested to be related to the Jahn–Teller effect in CuO6 coordination polyhedra. For this reason the hypothesis of the phase transition of malachite, Cu2CO3(OH)2, to a rosasite structure at high pressure, as a result of the reduced Jahn–Teller effect, has been tested and confirmed by powder and single-crystal diffraction structural studies: above 6 GPa the malachite structure is no longer stable and transforms to a RS structure. RS Cu2CO3(OH)2 is 3% more dense than malachite and the bulk modulus is remarkably higher, 80 (2) GPa compared with 48 (4) GPa. The longer apical Cu—O bonds in the distorted Me1 octahedral site are progressively shortened with increasing pressure, revealing a decrease in the Jahn–Teller effect at high pressure. The transition has a first-order character, is reversible with a significant hysteresis, and there is no evidence of any intermediate phase between the two structures. We then have further evidence that in the Me2(CO3)(OH)2 compounds, the two main structural types, MS and RS, are closely related. The former structure is stabilized only when Cu is the prevalent cation in the octahedral sites, and it can transform directly to the RS as a function of thermodynamic changes.

The relative stabilities of the copper/zinc solid solutions of hydroxyl sulphates, carbonates, nitrates, chlorides and bromides were studied by attempting their preparation using a variety of methods. All of the naturally occurring solid solutions except rosasite were obtained as single phases. Rosasite crystallized in a mixture with malachite and calcium carbonate during a room temperature preparation from calcium carbonate, copper nitrate and zinc nitrate. The solid solution with the antlerite stoichiometry [endmember Cu3SO4(OH)4] as well as the nitrates were not produced by the methods employed. All of the natural polymorphs of Cu2(OH)3Cl were obtained and a new method for the preparation of botallackite is reported. Botallackite was found to be stable in solution for over a year, contrary to previous reports. A bromine-bearing analogue of botallackite was prepared. Compounds were characterized by X-ray diffractometry, which was used to determine the unit-cell parameters, and by atomic absorption spectroscopy. The relative instability of solid solutions with certain stoichiometries is discussed in terms of the Jahn-Teller effect and relative solubilities.

Cu/ZnO catalysts were prepared by the co-precipitation method with the addition of OP-10 (polyoxyethylene octylphenol ether) and were chemically and structurally characterized by means of XRD, BET, H 2 -TPR, CO-TPD and N 2 O-titration. The effect of OP-10 addition on the activity of Cu/ZnO for the slurry phase methanol synthesis at 150 °C was evaluated. The results showed that Cu/ZnO prepared with addition of 8% OP-10 (denoted as C8) exhibited the promoted activity for the methanol synthesis. The conversion of CO and the STY (space time yield) of methanol were 42.5% and 74.6% higher than those of Cu/ZnO prepared without addition of OP-10 (denoted as C0), respectively. The precursor of C8 contained more aurichalcite and rosasite, and the concerted effect of Cu-Zn in C8 was found to be stronger than that in C0. Compared with C0, C8 showed smaller particle size, lower reduction temperature and larger BET and Cu surface areas.

The Cu/ZnO system is a model for Cu/ZnO/Al2O3 catalysts, which are employed industrially for the synthesis of methanol. These catalysts are usually prepared from mixed basic carbonate precursors. A complex phase mixture, with constituents structurally related to the minerals rosasite andaurichalcite, is present at the industrially applied composition (Cu/Zn ≈ 70:30). Using minerals and phase-pure synthetic samples as references, a comprehensive characterisation of such a phase mixture, including the determination of the individual compositions of the different phases, has been attempted by complementary analytical laboratory techniques (XRD, TGA, IR). The results are critically discussed in light of the complexity of the system. A thermally very stable carbonate species ― well-known for mixed synthetic systems ― is also detected for the mineral reference samples. Significant amounts of amorphous phases are found to be present in the synthetic zincian malachite sample but not in synthetic aurichalcite or the catalyst precursor. A simplified explanation for the shift of the characteristic 20 reflection of the malachite structure as a function of Zn incorporation based on the varying average Jahn–Teller distortion of the MO6 octahedra is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu 2+ ) 5 (CO 3 ) 2 (OH) 6 . XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm −1 is assigned to the ν 1 (CO 3 ) 2− symmetric stretching mode. Three Raman bands assigned to the ν 3 (CO 3 ) 2− antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm −1 . Multiple Raman bands are observed in 800–850 cm −1 and 720–750 cm −1 regions and are attributed to ν 2 and ν 4 bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm −1 is attributed to the δ OH deformation mode.

Raman spectroscopy at both 298 and 77K has been used to study a series of selected natural smithsonites from different origins. An intense sharp band at 1092 cm-1 is assigned to the CO32- symmetric stretching vibration. Impurities of hydrozincite are identified by a band around 1060 cm-1. An additional band at 1088 cm-1 is observed in the 298 K spectra but not in the 77K spectra is attributed to a CO32- hot band. Raman spectra of smithsonite show a single band in the 1405 to 1409 cm-1 range assigned to the ν3 (CO3)2- antisymmetric stretching mode. The observation of additional bands for the ν3g modes for some smithsonites is significant in that it shows distortion of the ZnO6 octahedron No ν2 bending modes are observed for smithsonite. A single band at 730 cm-1 is assigned to the ν4 in phase bending mode. Multiple bands be attributed to the structural distortion are observed for the carbonate ν4 in phase bending modes in the Raman spectrum of hydrozincite with bands at 733, 707 and 636 cm-1. An intense band at 304 cm-1 is attributed to the ZnO symmetric stretching vibration.

Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2, 3, 4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5, 6, 7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2, 3, 8, 9, 10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.

Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K and complimented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the structure is the same as malachite i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2- symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm-1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 A whereas for pokrovskite the distances are 3.280 and 2.999 A. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm-1 and the 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure.

This paper presents the mineralization of five medium-size limestone-caves and eleven skarn-hosted caves from the upper part of Cri?ul B¾ isei River (Bihor Mountains). Apart from berlinite - AlPO4, the other minerals reported from the limestone caves are common carbonates, phosphates or oxy- hydroxides. In turn, the skarn-hosted caves contain a diversity of minerals, including wittichenite, luzonite, natrolite, norsethite, rosasite, glaukosphaerite, aurichalcite, azurite, malachite and chalcanthite. Five of these minerals have never before been identified in a cave environment and moreover, three are new occurrences in Romania. Some of these minerals are hydrothermal in origin, whereas alteration and/or hydration of primary hydrothermal minerals formed the others. Considering the mineral assemblage, the morphology and the position of cavities within the skarn bodies, we assume these minerals formed during one of the following stages: hydrothermal, hydrothermal/vadose or vadose.

A Cu–Zn–Al precursor (CZA) was synthesized efficiently by coprecipitation of the corresponding cations with sodium carbonate at constant pH and temperature. The starting precursor contained a mixture of two hydroxycarbonate phases: rosasite and a Cu–Zn hydrotalcite-like phase. The thermal decomposition was studied by conventional thermal methods (TGA, DTA and EGA-MS) as well as by in situ FTIR spectroscopy (DRIFT). Analysis of the CZA precursor showed similar results by both procedures. Dehydration, dehydroxylation and decarbonation of the precursor were analysed in situ by monitoring the hydroxyl and carbonate infrared bands. A Cu–Zn hydrotalcite phase, one of the components of the CZA precursor, was also prepared independently. A detailed FTIR study revealed an interesting effect upon heating this hydrotalcite. At 373–423 K, a carbonate rearrangement in the interlayer space takes place during the loss of interlayer water. Carbonate groups change from their symmetrical coordination with interlayer water molecules to an arrangement involving the OH groups of the octahedral M(OH)m layers. This phenomenon certainly takes place in the CZA material as well but, in this case, it cannot be observed, probably due to the complexity of the material formed by two hydroxycarbonate phases.

The composition of a series of hydroxycarbonate precursors to copper/zinc oxide methanol synthesis catalysts prepared under conditions reported as optimum for catalytic activity has been studied. Techniques employed included thermogravimetry (TG), temperature-programmed decomposition (TPD), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman and FTIR spectroscopies. Evidence was obtained for various structural phases including hydrozincite, copper hydrozincite, aurichalcite, zincian malachite and malachite (the concentrations of which depended upon the exact Cu/Zn ratio used). Significantly, previously reported phases such as gerhardite and rosasite were not identified when catalysts were synthesized at optimum solution pH and temperature values, and after appropriate aging periods. Calcination of the hydroxycarbonate precursors resulted in the formation of catalysts containing an intimate mixture of copper and zinc oxides. Temperature-programmed reduction (TPR) revealed that a number of discrete copper oxide species were present in the catalyst, the precise concentrations of which were determined to be related to the structure of the catalyst precursor. Copper hydrozincite decomposed to give zinc oxide particles decorated by highly dispersed, small copper oxide species. Aurichalcite appeared to result ultimately in the most intimately mixed catalyst structure whereas zincian malachite decomposed to produce larger copper oxide and zinc oxide grains. The reason for the stabilization of small copper oxide and zinc oxide clusters by aurichalcite was investigated by using carefully selected calcination temperatures. It was concluded that the unique formation of an ‘anion-modified’ oxide resulting from the initial decomposition stage of aurichalcite was responsible for the ‘binding’ of copper species to zinc moieties.

The thermal decomposition of Cu-Zn-Al hydroxycarbonate precursors to obtain water-gas shift catalysts was studied by employing a variety of experimental techniques. A set of six samples containing 34 wt% of Cu and different Al/Zn ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary precursors contained hydrotalcite, aurichalcite and/or rosasite phases. Malachite and hydrozincite were determined in binary Cu/Al and Cu/Zn samples, respectively. The precipitates decomposed in three endothermic transformations in the temperature ranges 363–453 K, 453–673 K and 673–923 K. In the first step (ΔW=0–9%), the hydrotalcite-containing samples lost the crystallization water of the hydrotalcite phase. In the middle-temperature transition (ΔW=18–30%), the samples were completely dehydroxylated and simultaneously eliminated a proportion of the carbonate ions through a two-step dehydroxylation/decarbonation process. The high-temperature transformation (ΔW=3–7%) corresponded to the final decarbonation of the samples. Mixed oxides with a high dispersion of copper were obtained from hydrotalcite-containing precursors: the higher the amount of hydrotalcite in the precursor, the lower the CuO crystallite size in the resulting mixed oxide.

Bechererite is a new mineral found on dump material from the Tonopah-Belmont mine, Maricopa County, Arizona, U.S.A. It occurs as thin elongated crystals, commonly in hemispherical aggregates, and it is associated with rosasite, hydrozincite, willemite, smith- sonite, paratacamite, and boleite. Bechererite is light green, transparent with vitreous lus- ter, and has perfect cleavage parallel to {OO I}. It has a density of 3.45(5) glcm3 and a Mohs hardnessof 2-3. Optically,it is uniaxial(-) with ~ = 1.611(1) and w = 1.705(1). The empirical formula (based on 21 0 atoms) is (Zn4.93Cu1.ol)ZnlOH)13(Sl.loSio.9S)(OS.30(0H)2.70), simplified to (Zn,Cu)6Zn2(OH)13((S,Si)(0,OH)4)2' The strongest lines in the X-ray powder

The activity and structure-sensitivity of the water-gas shift (WGS) reaction over Cu Zn Al mixed oxide catalysts were studied. Three sets of samples with different Cu/Zn and (Cu+Zn)/Al atomic ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary hydroxycarbonate precursors contained hydrotalcite, aurichalcite and/or rosasite phases. The decomposed precursors contained CuO, ZnO, ZnAl 2 O 4 , and Al 2 O 3 . The relative proportion of these phases depended on both the chemical composition of the sample and the calcination temperature employed for decomposing the precursor. After activation with hydrogen, samples were tested for the WGS reaction at 503 K. The turnover frequency of the eighteen samples tested was essentially the same (0.2–0.3 s −1 ) irrespective of changing the copper metal surface area between 3 and 35 m 2 /g Cu and the metallic copper dispersion between 0.5 and 5.0%. This indicated that the WGS reaction is a structure-insensitive reaction, as the specific reaction rate r 0 (mol CO/h/g Cu) is always proportional to the copper metal surface area. Preparation of mixed oxides with a high copper dispersion is therefore required for obtaining more active catalysts. It was found that the value of the metallic copper dispersion is related to the amount of hydrotalcite contained in the hydroxycarbonate precursor: the higher the hydrotalcite content in the precursor, the higher the copper metal dispersion in the resulting catalyst and, as a consequence, the higher the catalyst activity. Ternary Cu/ZnO/Al 2 O 3 catalysts exhibited a substantially faster WGS activity than binary Cu/ZnO catalysts. The addition of aluminium, although inactive for the WGS reaction, is required for improving the catalyst performance.

The Darhib mine is one of the several talc deposits in the Hamata area of southeastern Egypt. Several specimens of minerals coming from this mine were subjected to complementary investigation by micro-Raman spectrometry and scanning electron microscopy. The difficulty in their identification is the appearance of most of them: they are all very small and only visible under the mineral binocular microscope(×10 - ×40). They appear as small crystals in fissures and holes and a visual determination on colour and crystal gives only a guess of what kind of mineral it could be. Therefore, only after analyzing them by micro-Raman and scanning electron microscopy it was possible to identify their structure and they can be divided in three main groups: one is quite generic and several minerals of different species were identified, such as quartz, talc, mottramite and chrysocolla, very common in the talc mine (these ones are Si-based minerals); the other one is constituted by four samples which are Zn and/or Cu rich, which means minerals of the rosasite or aurichalcite groups; the last group is constituted by two samples containing mainly Pb..

The crystal structures of malachite Cu2(OH)2CO3 and rosasite (Cu,Zn)2(OH)2CO3, though not isotypic, are closely related. A previously proposed approach explaining this relation via a common hypothetical parent structure is elaborated upon on the basis of group–subgroup considerations, leading to the conclusion that the aristotype of malachite and rosasite should crystallize in the space group Pbam (No. 55). An ICSD database search for actual representatives of this aristotype leads to the interesting observation that the structure type of ludwigite (Mg,Fe)2FeO2BO3, which is adopted by several natural and synthetic oxide orthoborates M 3O2BO3, is closely related to the proposed malachite–rosasite aristotype and thus to the malachite–rosasite family of hydroxide carbonates M 2(OH)2CO3 in general. Relations within both structure families and their analogies are summarized in a joint simplified Bärnighausen tree.

In the present paper we report combined experimental and theoretical studies of the UV-vis-NIR spectra of the mineral compounds malachite, rosasite, and aurichalcite and of the precursor compounds for Cu/ZnO catalysts. For the copper species in the minerals the crystal field splitting and the vibronic coupling constants are estimated using the exchange charge model of the crystal field accounting for the exchange and covalence effects. On this basis the transitions responsible for the formation of the optical bands arising from the copper centers in minerals are determined and the profiles of the absorption bands corresponding to these centers are calculated. The profiles of the absorption bands calculated as a sum of bands of their respective Cu species are in quite good agreement with the experimental data. In agreement with crystal chemical considerations, the Zn ions were found to be preferentially located on the more regular, i.e., less distorted, octahedral sites in zincian malachite and rosasite, suggesting a high degree of metal ordering in these phases. This concept also applies for the mineral aurichalcite, but not for synthetic aurichalcite, which seems to exhibit a lower degree of metal ordering. The catalyst precursor was found to be a mixture of zincian malachite and a minor amount of aurichalcite. The best fit of the optical spectrum is obtained assuming a mixture of contributions from malachite (0% Zn) and rosasite (38% Zn of [Zn + Cu]), which is probably due to the intermediate Zn content of the precursor (30%).

It is shown that Raman spectra and thermal analysis data (TGA and DSC) both discriminate among the hydroxycarbonate precursors that lead to successful Cu Zn - containing catalysts and those that lead to inactive catalysts. For binary Cu/Zn catalysts, the optimum precursor is single-phase three-dimensional aurichalcite, (Cu,Zn)5(OH)6(CO3)2, which is readily distinguished by these techniques from undesirable precursor materials such as copper hydroxynitrate [Cu2(OH)3NO3], rosasite [(Cu,Zn)2(OH)2CO3] and hydrozincite [Zn5(OH)6(CO3)2]. Ternary Cu Zn/Al catalysts are successfully made via a layer-structured hydrotalcite-like precursor, i.e., (Cu,Zn)6Al2(OH)16CO3·4H2O. Thermal decomposition and infrared analyses indicate that the interlayer carbonate anion is retained by the ternary catalyst even to calcination temperatures of 350–450 °C, which has implications for the subsequent aqueous surface doping treatments used to further promote these catalysts

Synthetic zincian malachite samples (Cu1–xZnx)2(OH)2CO3 with x = 0, 0.1, 0.2 and 0.3 were characterized by powder X-ray diffraction and optical spectroscopy. The XRD patterns of the samples up to x = 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the zinc content. In contrast, the sample with a nominal zinc content x = 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)5(OH)6(CO3)2 as an additional phase. Based on the lattice parameter variations, the zinc content of the zincian malachite component in this sample is estimated to be x ≈ 0.27, which seems to represent the maximum possible substitution in zincian malachite under the synthesis conditions applied. The results are discussed in relation to preparation of Cu/ZnO catalysts and the crystal structures of the minerals malachite and rosasite. One striking difference between these two structurally closely related phases is the orientation of the Jahn–Teller elongated axes of the CuO6 octahedra in the unit cell, which seems to be correlated with the placement of the monoclinic β angle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn2(OH)2CO3 phase of higher orthorhombic symmetry. In addition to the crystallographic analysis, optical spectroscopy proves to be a useful tool for estimation of the Cu:Zn ratio in (Cu1–xZnx)2(OH)2CO3 samples.

Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at approximately 3401 and 3311 cm-1. Two intense bands observed at approximately 1096 and 1046 cm-1 are assigned to nu1(CO3)2- symmetric stretching vibration and the delta OH deformation mode. Multiple bands are found in the 800-900 and 650-750 cm-1 regions attributed to the nu2 and nu4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C2v or Cs. A band at approximately 560 cm-1 is assigned to a CuO stretching mode.

The ability of near infrared reflectance spectroscopy to classify the rosasite group minerals from spectral characteristics is demonstrated. NIR spectroscopy can be regarded as an alternative tool for structure analysis. The spectra show that rosasite group minerals with different cations can be distinguished. Ni2+ in nullaginite [Ni2(CO3)(OH)2] is conspicuous through a single broad band absorption feature at 8525 cm−1, extended from 11,000 to 7000 cm−1. The effect of Ni on Cu is seen in the spectrum of glaukosphaerite [(Cu, Ni)2(CO3)(OH)2] both by a red shift of the spectrum and reduction in intensity of bands with variable positions of band maxima for Cu2+ at 6995 cm−1and Ni2+ at 7865 cm−1. The spectrum of rosasite [(Cu, Zn)2(CO)3(OH)2] is characterised by Cu2+ band at 7535 cm−1. Kolwezite [(Cu, Co)2(CO)3(OH)2] is a spectral mixture of Cu and Co but optically separated by Co2+ and Cu2+ peaks at 8385 and 7520 cm−1. Vibrational spectra of carbonates show a number of bands in the 7000–4000 cm−1 region attributable to overtones, combination of OH stretching and deformation modes. They appear to be uniform in nature since the structure of rosasite group minerals is identical. The complexity of these features varies between samples because of the variation in composition and hence is useful for discriminating different hydrous carbonates.

The crystal structures of glaukosphaerite (Cu,Ni)2(CO3)(OH)2 and pokrovskite Mg2(CO3)(OH)2, two carbonates belonging to the malachite-rosasite group, have been determined from powder diffraction data, and refined up to wRp = 3.94% and 1.63% respectively. Both minerals are isostructural with rosasite (Cu,Zn)2(CO3)(OH)2, with P 21/ a space group and cell parameters a =12.0613(4) A, b = 9.3653(4), c = 3.1361(1), β = 98.085(5)° for glaukosphaerite and a = 12.2396(4), b = 9.3506(4), c = 3.1578(1), β = 96.445(5)° for pokrovskite. Their structures are built up by ribbons of edge-sharing octahedra running along the c -axis; the ribbons are linked together through corner-sharing giving rise to corrugated layers parallel to (100) that are interconnected through carbonate groups. The same layers and carbonate groups, arranged in a different orientation with respect to the symmetry operators, build up the structure of malachite: the relationships between the rosasite-like and the malachite-like structural models are discussed. The octahedral distortion of the two independent Me sites in the malachite-rosasite known structures is evaluated and attributed to the Jahn-Teller effect of Cu2+. According to the available chemical data for the examined material, a partial occupancy in Mg sites of pokrovskite is maintained, with a coupled partial substitution of hydroxyls by water molecules. On the basis of the structural results, the difficulties and ambiguities in the powder pattern indexing by preceeding authors are discussed and explained, and reliable guesses for the arrangements of kolwezite and nullaginite are drawn.

15 páginas, 8 figuras, Chemical and textural studies show fibrous rosasite crystals, with a spread Cu : Zn ratio, occuring in a calcite matrix together with goethite, psilomelane, quartz and saponite in oxidation zones of copper ore deposits. Aurichalcite occurs also as fibrous crystals and has a more fixed composition (Cu : Zn ratio is 1.3 : 3.7). Aurichalcite sample also contains prismatic hemimorphite. The nature of the copper ion and its site symmetry in rosasite and aurichalcite were investigated using a combination of optical absorption and EPR spectroscopy. Optical absorptions of rosasite exhibited three bands due to Cu2+ in tetragonally elongated octahedral site and the parameters evaluated from the observed band positions are Dq = 1480, Ds = 2330 and Dt = 410cm-1. The EPR features observed in rosasite (g > g||) is an indication of predominant interactions within the copper ions (Cu Zn). Optical and EPR spectra of aurichalcite sample account for Cu2+ ion in the distorted octahedron site. The molecular structures of the two copper zinc carbonate hydroxide minerals were also studied by FTIR spectroscopy. The infrared spectra of the two minerals are different in line with differences in crystal structure and composition. The shift towards lower wave numbers of the carbonate bands and splitting of bands are more in aurichalcite than the other. This indicates that the symmetry of CO32- ion in both the minerals is lowered from D3h to C2v or Cs and distortion is more in aurichalcite., This work was financed by Research Project BT2000-0582 (S.E.U.I:D.-M.C.T., Spain)

Cu/Zn Hydroxycarbonates obtained by co-precipitation of Cu(2+) and Zn(2+) with Na(2)CO(3) have been investigated regarding phase formation and thermal decomposition in two series with varying Cu/Zn ratios prepared according to the decreasing pH and constant pH method. Hydrozincite, aurichalcite and (zincian)-malachite were found to form at differing Cu/Zn ratios for both series. For the constant pH preparation the Cu/Zn ratio in zincian-malachite was close to the nominal values whereas excess values were found for the decreasing pH samples. The degree of crystallinity as well as the thermal decomposition temperatures were lower for the constant pH series. All samples containing aurichalcite revealed an unexpected decomposition step at high temperatures evolving exclusively CO(2). The differences in composition and microstucture were traced back to the different pathways of solid formation for the two preparation methods. Substantial changes were observed during the post-precipitation processes of ageing and washing. The effects were studied in detail on samples with a cation ratio of Cu/Zn 70:30 mol %. Ageing of the precipitates in their own solutions is accompanied by a spontaneous crystallization of the initially amorphous solids. The decreasing pH sample develops from a hydroxy-rich material comprising basic copper nitrate (gerhardtite) as an intermediate. Only small changes in the chemistry of the samples were detected for the constant pH precipitation. The findings are summarised into a scheme of solid formation processes that explains the phenomenon of a "chemical memory" of the precipitates when they are converted into Cu/ZnO model catalysts.

A series of Cu/Zn/Al/Zr catalysts were synthesized by calcination of hydrotalcite-containing precursors with different Cu2+/Zn2+ atomic ratios (n). Two other catalysts (n = 2) were also prepared via phase-pure hydrotalcite-like and conventional rosasite precursors for comparison. XRD and UV-Vis-NIR DRS characterizations demonstrate that most Cu2+ of hydrotalcite-containing materials did not enter the layer structure. The Cu dispersion of the catalysts decreases with the increase of Cu content, while both the exposed Cu surface area and the Cu+ and Cu0 content on the reduced surface reach a maximum when n is 2. The catalytic performance for the methanol synthesis from CO2 hydrogenation was also tested. The catalytic activity and selectivity of the catalysts (n = 0.5–4) via hydrotalcite-containing precursors rise first and then decrease with increasing Cu2+/Zn2+ ratios, and the optimum performance is obtained over the catalyst with Cu2+/Zn2+ = 2. Moreover, the Cu/Zn/Al/Zr catalyst (n = 2) via hydrotalcite-containing precursor exhibits the best catalytic performance, which is mainly due to the maximum content of active species compared with another two catalysts derived from different precursors.

The coprecipitated hydroxycarbonate precursor of the methanol synthesis and shift reaction catalyst based on 30 at.% copper and 70 at.% zinc oxide, which was previously reported to be a mixture of hydrozincite Zn5(CO3)2(OH)6 and rosasite (Cu,Zn)2(CO3)(OH)2 (R. G. Herman, K. Klier, G. W. Simmons, B. P. Finn, J. B. Bulko, and T. P. Kobylinski, J. Catal. 56, 407, 1979) or a single-phase hydrozincite (G. Petrini, F. Montino, A. Bossi, and G. Gaybassi, in “Studies in Surface Science and Catalysis. Preparation of Catalysis III” (G. Poncelet, P. Grange, and P. A. Jacobs, Eds.), Vol. 16, p. 735. Elsevier, The Netherlands, 1983), is herein shown to be a single-phase aurichalcite (Cu0.3Zn0.7)5(CO3)2(OH)6. The orthorhombic B2212 aurichalcite is crystallograpically distinct from the monoclinic C 2 m hydrozincite, although these two compounds have the same ratio of metal ions to carbonate and hydroxyl anions. Both aurichalcite and hydrozincite are chemically and structurally distinct from the monoclinic P2 1 a rosasite. The earlier erroneous assignments are attributed to the structural similarity of the three hydroxycarbonates in question. An energy-dispersive characteristic X-ray emission analysis of individual particles in the scanning transmission electron microscope reveals a uniform distribution of copper and zinc at the analytical concentration Cu Zn = 30 70 . Precursors with less than 30% copper consist of mixtures of aurichalcite and hydrozincite.