A honeycomb filter includes: a honeycomb structure having porous partition walls disposed so as to surround cells, and plugging portions disposed at any one of ends on the inflow end face and the ends on the outflow end face, of cells. In a cross section perpendicular to an extending direction of the cells, a thickness T1 of the partition walls in a central portion including a center of gravity O of the cross section is 0.17 to 0.32 mm, a thickness T2 of the partition walls in an outer peripheral portion is 70 to 90% of the thickness T1, and the outer peripheral portion extends from an outer peripheral edge of the cross section of honeycomb structure by 6 to 12% of a radius r which is from the center of gravity O of the cross section to the outer peripheral edge.

A pillar-shaped honeycomb structure including an outer peripheral side wall, and a plurality of partition walls disposed on an inner peripheral side of the outer peripheral side wall, the plurality of partition walls partitioning a plurality of cells forming flow paths from a first end surface to a second end surface, wherein an average pore diameter of the partition walls measured by a mercury porosimeter is 10 μm or less, and when a cross section of the plurality of partition walls is observed with an X-ray microscope and porosities (%) of each partition wall is measured in a thickness direction from one surface to the other surface of each partition wall, an average porosity of each partition wall is 40 to 70%, and a difference between a maximum value and a minimum value of the porosity of each partition wall is 11% or less.

A honeycomb structure includes: a honeycomb structure portion which includes an outer peripheral wall, and partition walls disposed inside the outer peripheral wall and partitioning a plurality of cells forming flow paths from one end surface to the other end surface; and a pair of electrode layers provided on an outer surface of the outer peripheral wall so as to extend in a strip shape along a direction in which the cells extend and sandwich a central axis of the honeycomb structure portion; wherein a porosity P.sub.W of the partition walls is 30% to 55%, and a ratio of the porosity P.sub.W of the partition walls to a porosity P.sub.O of the outer peripheral wall (P.sub.W/P.sub.O) satisfies 1<P.sub.W/P.sub.O≤1.8.

Proposed inventions are a recipe of denitrification-oxidation complex catalyst containing an SCR catalyst and an oxidation catalyst to simultaneously remove nitrogen oxides, carbon monoxide, hydrocarbons, and ammonia, a manufacturing method thereof, an exhaust gas treatment method using the denitrification-oxidation complex catalyst, and an SCR denitrification system including the denitrification-oxidation complex catalyst. The denitrification-oxidation complex catalyst simultaneously removes nitrogen oxides, carbon monoxide, hydrocarbons, and ammonia and exhibits an increased catalytic effect compared to the cases where the denitrification catalyst used alone and the denitrification and the oxidation catalyst ratios are and not properly balanced. When the denitrification-oxidation complex catalyst is applied to an SCR denitrification system, the structure is simplified, space is saved, cost is reduced, and catalyst maintenance is easy.

A heating unit for an exhaust-gas system of an internal combustion engine includes a heating-unit housing for conducting an exhaust-gas in a main flow direction. A plurality of heating elements are arranged in the heating-unit housing and are shaped in a meandering manner. Each heating element has a plurality of plate-like heating sections which follow one another in a heating-element longitudinal direction. The heating sections of each heating element are connected to one another via respective connecting sections. Each heating element has two connection regions which are arranged at a distance from one another. In each connection region, the heating elements are electrically conductively connected to a connection region of a further heating element.

A particulate filter 23 is configured by being provided with, arranged side by side, a plurality of honeycomb-shaped segments 29, 30, 31 having a plurality of cells 32. The density of cells in the segments 30, 31 disposed in the outer circumference part is set to be lower than the density of cells in the segments 29 disposed in the center part. In addition, the segments 30, 31 disposed in the outer circumference part are configured so that the density of the cells 32 becomes lower as the area of the end face becomes smaller.

A plugged honeycomb structure includes a honeycomb structure body having a porous partition wall disposed to surround a plurality of cells; and a plugging portion disposed at one end of the cells, wherein, in a section orthogonal to the extending direction of the cell, the cells each have a shape that is polygon, and one of the inflow cells and another are adjacent to each other with the partition wall therebetween, and in the section orthogonal to the extending direction of the cell, a total area of the inflow cell is larger than a total area of the outflow cell, a porosity of the partition wall is 38% or more, a thickness of the partition wall is 125 μm or more and 280 μm or less, a cell density of the honeycomb structure body is 31.0 cells/cm.sup.2 or more, and an air-permeability resistance of the partition wall is 4.5×10.sup.7Pa.Math.s/m.sup.2 or less.

A catalyst for gasoline engine exhaust gas after-treatment, comprising Pt and optionally at least one other platinum group metal on a hydrothermal stable support material which is coated onto a gasoline particulate filter. The catalyst oxidizes particulate matter trapped in the gasoline particulate filter under low temperature and abates NO.sub.x, CO and HC. Also a process for preparing the catalyst is disclosed, and a method for after-treatment of gasoline engine exhaust gas using the catalyst is disclosed.

A diesel exhaust treatment system for treating exhaust gas from a diesel engine comprising at least one diesel oxidation catalyst (DOC), at least one diesel particulate filter (DPF), at least one diesel exhaust fluid mixing chamber and at least one selective catalytic reduction converter (SCR). In one desirable embodiment, two DOCs, two DPFs, two SCRs, and two diesel exhaust fluid mixing chambers are arranged in parallel. The disclosed system is configured to reduce back pressure and increase urea vaporization while effectively using available space and providing improved access to components. The system can be coupled to a vehicle frame rail, such as the frame rail of a heavy duty truck.

A diesel exhaust treatment system for treating exhaust gas from a diesel engine comprising at least one diesel oxidation catalyst (DOC), at least one diesel particulate filter (DPF), at least one diesel exhaust fluid mixing chamber and at least one selective catalytic reduction converter (SCR). In one desirable embodiment, two DOCs, two DPFs, two SCRs, and two diesel exhaust fluid mixing chambers are arranged in parallel. The disclosed system is configured to reduce back pressure and increase urea vaporization while effectively using available space and providing improved access to components. The system can be coupled to a vehicle frame rail, such as the frame rail of a heavy duty truck.