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  • 1
    Electronic Resource
    Electronic Resource
    Shape-selective alkylation of biphenyl over mordenites: effects of dealumination on shape-selectivity and coke deposition (1994)
    Springer
    Catalysis letters 26 (1994), S. 181-187 
    Details
    ISSN: 1572-879X
    Keywords: shape-selective catalysis ; biphenyl ; isopropylation ; H-mordenite ; carbonaceous deposits ; encapsulated biphenyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract To understand the relationships between shape-selectivity and coke deposition in the alkylation of biphenyl over H-mordenite (HM), thermogravimetric analyses were examined for the catalyst after the reaction. The coke deposition during the catalysis was very severe over HM with low SiO/Al2O3 ratio, however, dealumination enhanced the decrease of coke deposition. Over highly dealuminated HM, volatile organic compounds, mainly biphenyl derivatives, were observed in addition to carbonaceous deposits. The deposits are produced from biphenyl derivatives on acid sites in the HM pore, and the ease of their formation is governed by acid site density and acid strength. The decrease of carbonaceous deposits and the increase of encapsulated biphenyl derivatives are related with the increase of both selectivity and yield of 4,4′-diisopropylbiphenyl (4,4′-DIPB). The increase of reaction temperature up to 250°C enhanced the catalysis over highly dealuminated HM, however, further increase of the temperature resulted in extensive decrease of the selectivity of 4,4′-DIPB. Coke deposition also increased with the temperature although its level was low. The composition of 4,4′-DIPB in encapsulated DIPB isomers remained as high as 80% in spite of a change of the distribution of bulk products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00824043
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  • 2
    Electronic Resource
    Electronic Resource
    Shape-selective alkylation of biphenyl over mordenite: cerium exchanged sodium mordenite and unmodified H-mordenite with low SiO2/Al2O3 ratio (1994)
    Springer
    Catalysis letters 27 (1994), S. 315-322 
    Details
    ISSN: 1572-879X
    Keywords: Shape-selective catalysis ; biphenyl ; isopropylation ; cerium exchanged sodium mordenite ; H-mordenite ; propylene pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Liquid phase isopropylation of biphenyl with propylene was studied over a cerium exchanged sodium mordenite (Ce/NaM25) and a H-mordenite (HM25) with the same SiO2/Al2O3 ratio of 25. Shape-selective catalysis occurred to give 4,4′-diisopropylbiphenyl (4,4′-DIPS) in high selectivity over Ce/NaM25 under any propylene pressures. HM25 gave 4,4′-DIPS shape-selectively under high propylene pressures. However, the reaction was severely deactivated at a conversion of ca. 60% under such a low pressure as 0.8 kg/cm2 because of coke formation in the pore. The yields of 4-isopropylbiphenyl (4-IPBP) and 4,4′-DIPB decreased with the increase of those of 3-IPBP and 3,4′-DIPB because of non-selective alkylation and isomerization at external acid sites that are alive in spite of severe deactivation. No significant isomerization of 4,4′-DIPB over Ce/NaM25 was observed even at low propylene pressure. In the case of HM25, the isomerization of 4,4′-DIPB to 3,4′-DIPB occurred significantly under low propylene pressures, while it decreased under high pressure. These differences are ascribed to the differences of nature of acid sites between Ce/NaM25 and HM25 zeolites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813918
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of cingulate cortical lesions on avoidance learning and training-induced unit activity in rabbits (1991)
    Springer
    Experimental brain research 86 (1991), S. 585-600 
    Details
    ISSN: 1432-1106
    Keywords: Multi-unit activity ; Conditioning and learning ; Neural basis of learning ; Limbic functions ; Caudate nucleus ; Medial dorsal thalamic nucleus ; Behaving rabbits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study extends an ongoing analysis of the neural mediation of discriminative avoidance learning in rabbits. Electrolytic lesions encompassing anterior and posterior cingulate cortex (area 24 and 29) or ibotenic acid lesions in area 24 only were made prior to avoidance conditioning wherein rabbits learned to step in response to a tone conditional stimulus (CS+) in order to avoid a brief, response-terminated 1.5 mA. foot-shock unconditional stimulus (US). The US was presented 5 s after CS+ onset, in the absence of a prior stepping response. The rabbits also learned to ignore a different tone (CS-) not followed by the US. Multi-unit activity of the caudate and medial dorsal (MD) thalamic nuclei, projection targets of the cingulate cortex, was recorded during learning in all rabbits. Activity was also recorded in area 29 in the rabbits with area 24 lesions. Learning in rabbits with combined lesions was severely impaired and it was moderately retarded after lesions in area 24. MD thalamic and caudate training-induced neuronal discharge increments elicited by the CS+ were enhanced in rabbits with lesions, suggesting a suppressive influence of cingulate cortical projections on this activity. Early-, but not late-developing training-induced unit activity in area 29c/d was absent in rabbits with area 24 lesions, indicating that area 24 is a source of early-developing area 29 plasticity. These results are consistent with hypotheses of a theoretical working model, stating that: a) learning depends on the integrity of two functional systems, a mnemonic recency system comprised by circuitry involving area 24 and the MD nucleus and a mnemonic primacy system comprised by circuitry involving area 29 and the anterior thalamic nuclei; b) corticothalamic information flow in these systems suppresses thalamic CS elicited activity in trained rabbits; c) corticostriatal information flow is involved in avoidance response initiation. An absence of rhythmic theta-like neuronal bursts in area 29b in rabbits with area 24 lesions is attributable to passing fiber damage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230532
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    Paper (German National Licenses)
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